@article{king_nemanich_davis_2015, title={Band alignment at AlN/Si (111) and (001) interfaces}, volume={118}, ISSN={["1089-7550"]}, DOI={10.1063/1.4927515}, abstractNote={To advance the development of III-V nitride on silicon heterostructure semiconductor devices, we have utilized in-situ x-ray photoelectron spectroscopy (XPS) to investigate the chemistry and valence band offset (VBO) at interfaces formed by gas source molecular beam epitaxy of AlN on Si (001) and (111) substrates. For the range of growth temperatures (600–1050 °C) and Al pre-exposures (1–15 min) explored, XPS showed the formation of Si-N bonding at the AlN/Si interface in all cases. The AlN/Si VBO was determined to be −3.5 ± 0.3 eV and independent of the Si orientation and degree of interfacial Si-N bond formation. The corresponding AlN/Si conduction band offset (CBO) was calculated to be 1.6 ± 0.3 eV based on the measured VBO and band gap for wurtzite AlN. Utilizing these results, prior reports for the GaN/AlN band alignment, and transitive and commutative rules for VBOs, the VBO and CBO at the GaN/Si interface were determined to be −2.7 ± 0.3 and −0.4 ± 0.3 eV, respectively.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, Sean W. and Nemanich, Robert J. and Davis, Robert F.}, year={2015}, month={Jul} }
 @article{king_nemanich_davis_2015, title={Cleaning of pyrolytic hexagonal boron nitride surfaces}, volume={47}, ISSN={["1096-9918"]}, DOI={10.1002/sia.5781}, abstractNote={Hexagonal boron nitride (h‐BN) has recently garnered significant interest as a substrate and dielectric for two‐dimensional materials and devices based on graphene or transition metal dichalcogenides such as molybdenum disulfide (MoS2). As substrate surface impurities and defects can negatively impact the structure and properties of two‐dimensional materials, h‐BN surface preparation and cleaning are a critical consideration. In this regard, we have utilized X‐ray photoelectron spectroscopy to investigate the influence of several ex situ wet chemical and in situ thermal desorption cleaning procedures on pyrolytic h‐BN surfaces. Of the various wet chemistries investigated, a 10 : 1 buffered HF solution was found to produce surfaces with the lowest amount of oxygen and carbon contamination. Ultraviolet/ozone oxidation was found to be the most effective ex situ treatment for reducing carbon contamination. Annealing at 1050 °C in vacuum or 10−5 Torr NH3 was found to further reduce oxygen and carbon contamination to the XPS detection limits. Copyright © 2015 John Wiley & Sons, Ltd.}, number={7}, journal={SURFACE AND INTERFACE ANALYSIS}, author={King, Sean W. and Nemanich, Robert J. and Davis, Robert F.}, year={2015}, month={Jul}, pages={798–803} }
 @article{king_tanaka_davis_nemanich_2015, title={Hydrogen desorption from hydrogen fluoride and remote hydrogen plasma cleaned silicon carbide (0001) surfaces}, volume={33}, ISSN={["1520-8559"]}, DOI={10.1116/1.4921526}, abstractNote={Due to the extreme chemical inertness of silicon carbide (SiC), in-situ thermal desorption is commonly utilized as a means to remove surface contamination prior to initiating critical semiconductor processing steps such as epitaxy, gate dielectric formation, and contact metallization. In-situ thermal desorption and silicon sublimation has also recently become a popular method for epitaxial growth of mono and few layer graphene. Accordingly, numerous thermal desorption experiments of various processed silicon carbide surfaces have been performed, but have ignored the presence of hydrogen, which is ubiquitous throughout semiconductor processing. In this regard, the authors have performed a combined temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) investigation of the desorption of molecular hydrogen (H2) and various other oxygen, carbon, and fluorine related species from ex-situ aqueous hydrogen fluoride (HF) and in-situ remote hydrogen plasma cleaned 6H-SiC (0001) surfaces...}, number={5}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={King, Sean W. and Tanaka, Satoru and Davis, Robert F. and Nemanich, Robert J.}, year={2015}, month={Sep} }
 @article{king_davis_carter_schneider_nemanich_2015, title={Hydrogen desorption kinetics for aqueous hydrogen fluoride and remote hydrogen plasma processed silicon (001) surfaces}, volume={33}, ISSN={["1520-8559"]}, DOI={10.1116/1.4926733}, abstractNote={The desorption kinetics of molecular hydrogen (H2) from silicon (001) surfaces exposed to aqueous hydrogen fluoride and remote hydrogen plasmas were examined using temperature programmed desorption. Multiple H2 desorption states were observed and attributed to surface monohydride (SiH), di/trihydride (SiH2/3), and hydroxide (SiOH) species, subsurface hydrogen trapped at defects, and hydrogen evolved during the desorption of surface oxides. The observed surface hydride species were dependent on the surface temperature during hydrogen plasma exposure with mono, di, and trihydride species being observed after low temperature exposure (150 °C), while predominantly monohydride species were observed after higher temperature exposure (450 °C). The ratio of surface versus subsurface H2 desorption was also found to be dependent on the substrate temperature with 150 °C remote hydrogen plasma exposure generally leading to more H2 evolved from subsurface states and 450 °C exposure leading to more H2 desorption from s...}, number={5}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={King, Sean W. and Davis, Robert F. and Carter, Richard J. and Schneider, Thomas P. and Nemanich, Robert J.}, year={2015}, month={Sep} }
 @article{king_nemanich_davis_2015, title={Photoemission investigation of the Schottky barrier at the Sc/3C-SiC (111) interface}, volume={252}, ISSN={["1521-3951"]}, DOI={10.1002/pssb.201451340}, abstractNote={The Schottky barrier and interfacial chemistry for interfaces formed by evaporation of Sc onto 3C‐SiC (111)‐(1x1) surfaces at 600 °C has been investigated using in situ X‐ray and ultra‐violet photoelectron spectroscopy (XPS and UPS) and low energy electron diffraction (LEED). Sc was observed to grow in a two‐dimensional manner and exhibit a (1x1) LEED pattern up to thicknesses of ∼2 nm beyond which diffraction patterns were no longer observable. XPS measurements of these same films showed a clear reaction of Sc with the 3C‐SiC (111)‐(1x1) surface to form a ScSix and ScCx interfacial layer in addition to the formation of a metallic Sc film. XPS measurements also showed the deposition of Sc induced ∼0.5 eV of upward band bending resulting in a Schottky barrier of 0.65 ± 0.15 eV.}, number={2}, journal={PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS}, author={King, Sean W. and Nemanich, Robert J. and Davis, Robert F.}, year={2015}, month={Feb}, pages={391–396} }
 @article{king_davis_nemanich_2014, title={Desorption and sublimation kinetics for fluorinated aluminum nitride surfaces}, volume={32}, ISSN={["1520-8559"]}, DOI={10.1116/1.4891650}, abstractNote={The adsorption and desorption of halogen and other gaseous species from surfaces is a key fundamental process for both wet chemical and dry plasma etch and clean processes utilized in nanoelectronic fabrication processes. Therefore, to increase the fundamental understanding of these processes with regard to aluminum nitride (AlN) surfaces, temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) have been utilized to investigate the desorption kinetics of water (H2O), fluorine (F2), hydrogen (H2), hydrogen fluoride (HF), and other related species from aluminum nitride thin film surfaces treated with an aqueous solution of buffered hydrogen fluoride (BHF) diluted in methanol (CH3OH). Pre-TPD XPS measurements of the CH3OH:BHF treated AlN surfaces showed the presence of a variety of Al-F, N-F, Al-O, Al-OH, C-H, and C-O surfaces species in addition to Al-N bonding from the AlN thin film. The primary species observed desorbing from these same surfaces during TPD measurements included H2, H2O, HF, F2, and CH3OH with some evidence for nitrogen (N2) and ammonia (NH3) desorption as well. For H2O, two desorption peaks with second order kinetics were observed at 195 and 460 °C with activation energies (Ed) of 51 ± 3 and 87 ± 5 kJ/mol, respectively. Desorption of HF similarly exhibited second order kinetics with a peak temperature of 475 °C and Ed of 110 ± 5 kJ/mol. The TPD spectra for F2 exhibited two peaks at 485 and 585 °C with second order kinetics and Ed of 62 ± 3 and 270 ± 10 kJ/mol, respectively. These values are in excellent agreement with previous Ed measurements for desorption of H2O from SiO2 and AlFx from AlN surfaces, respectively. The F2 desorption is therefore attributed to fragmentation of AlFx species in the mass spectrometer ionizer. H2 desorption exhibited an additional high temperature peak at 910 °C with Ed = 370 ± 10 kJ/mol that is consistent with both the dehydrogenation of surface AlOH species and H2 assisted sublimation of AlN. Similarly, N2 exhibited a similar higher temperature desorption peak with Ed = 535 ± 40 kJ/mol that is consistent with the activation energy for direct sublimation of AlN.}, number={5}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={King, Sean W. and Davis, Robert F. and Nemanich, Robert J.}, year={2014}, month={Sep} }
 @article{king_davis_nemanich_2014, title={Gas source molecular beam epitaxy of scandium nitride on silicon carbide and gallium nitride surfaces}, volume={32}, ISSN={["1520-8559"]}, DOI={10.1116/1.4894816}, abstractNote={Scandium nitride (ScN) is a group IIIB transition metal nitride semiconductor with numerous potential applications in electronic and optoelectronic devices due to close lattice matching with gallium nitride (GaN). However, prior investigations of ScN have focused primarily on heteroepitaxial growth on substrates with a high lattice mismatch of 7%–20%. In this study, the authors have investigated ammonia (NH3) gas source molecular beam epitaxy (NH3-GSMBE) of ScN on more closely lattice matched silicon carbide (SiC) and GaN surfaces (<3% mismatch). Based on a thermodynamic analysis of the ScN phase stability window, NH3-GSMBE conditions of 10−5–10−4 Torr NH3 and 800–1050 °C where selected for initial investigation. In-situ x-ray photoelectron spectroscopy (XPS) and ex-situ Rutherford backscattering measurements showed all ScN films grown using these conditions were stoichiometric. For ScN growth on 3C-SiC (111)-(√3 × √3)R30° carbon rich surfaces, the observed attenuation of the XPS Si 2p and C 1s substrate core levels with increasing ScN thickness indicated growth initiated in a layer-by-layer fashion. This was consistent with scanning electron microscopy (SEM) images of 100–200 nm thick films that revealed featureless surfaces. In contrast, ScN films grown on 3C-SiC (111)-(3 × 3) and 3C-SiC (100)-(3 × 2) silicon rich surfaces were found to exhibit extremely rough surfaces in SEM. ScN films grown on both 3C-SiC (111)-(√3 × √3)R30° and 2H-GaN (0001)-(1 × 1) epilayer surfaces exhibited hexagonal (1 × 1) low energy electron diffraction patterns indicative of (111) oriented ScN. X-ray diffraction ω-2θ rocking curve scans for these same films showed a large full width half maximum of 0.29° (1047 arc sec) consistent with transmission electron microscopy images that revealed the films to be poly-crystalline with columnar grains oriented at ≈15° to the [0001] direction of the 6H-SiC (0001) substrate. In-situ reflection electron energy loss spectroscopy measurements determined the band-gap for the NH3-GSMBE ScN films to be 1.5 ± 0.3 eV, and thermal probe measurements indicated all ScN films to be n-type. The four point probe sheet resistance of the ScN films was observed to increase with decreasing growth temperature and decreased with unintentional oxygen incorporation. Hg probe capacitance–voltage measurements indicated ND-NA decreased with decreasing growth temperature from 1019 to 1020/cm3 for the lowest resistivity films to ≅5 × 1016/cm3 for the highest resistivity films. In-situ ultraviolet photoelectron spectroscopy measurements additionally showed the valence band maximum moving from 1.4 to 0.8 eV below the Fermi level with decreasing growth temperature consistent with the increased resistivity and reduction in carrier concentration. These results suggest that additional reductions in ScN carrier concentrations can be achieved via continued optimization of ScN growth conditions and selection of substrate orientation and surface termination.}, number={6}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={King, Sean W. and Davis, Robert F. and Nemanich, Robert J.}, year={2014}, month={Nov} }
 @article{king_nemanich_davis_2014, title={Valence and conduction band alignment at ScN interfaces with 3C-SiC (111) and 2H-GaN (0001)}, volume={105}, ISSN={["1077-3118"]}, DOI={10.1063/1.4894010}, abstractNote={In order to understand and predict the behavior of future scandium nitride (ScN) semiconductor heterostructure devices, we have utilized in situ x-ray and ultra-violet photoelectron spectroscopy to determine the valence band offset (VBO) present at ScN/3C-SiC (111) and 2H-GaN (0001)/ScN (111) interfaces formed by ammonia gas source molecular beam epitaxy. The ScN/3C-SiC (111) VBO was dependent on the ScN growth temperature and resistivity. VBOs of 0.4 ± 0.1 and 0.1 ± 0.1 eV were, respectively, determined for ScN grown at 925 °C (low resistivity) and 800 °C (high resistivity). Using the band-gaps of 1.6 ± 0.2 and 1.4 ± 0.2 eV previously determined by reflection electron energy loss spectroscopy for the 925 and 800 °C ScN films, the respective conduction band offsets (CBO) for these interfaces were 0.4 ± 0.2 and 0.9 ± 0.2 eV. For a GaN (0001) interface with 925 °C ScN (111), the VBO and CBO were similarly determined to be 0.9 ± 0.1 and 0.9 ± 0.2 eV, respectively.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={King, Sean W. and Nemanich, Robert J. and Davis, Robert F.}, year={2014}, month={Aug} }
 @article{reitmeier_einfeldt_davis_zhang_fang_mahajan_2010, title={Surface and defect microstructure of GaN and AlN layers grown on hydrogen-etched 6H-SiC(0001) substrates}, volume={58}, number={6}, journal={Acta Materialia}, author={Reitmeier, Z. J. and Einfeldt, S. and Davis, R. F. and Zhang, X. Y. and Fang, X. L. and Mahajan, S.}, year={2010}, pages={2165–2175} }
 @article{bishop_reynolds_molstad_stevie_barnhardt_davis_2009, title={On the origin of aluminum-related cathodoluminescence emissions from sublimation grown 4H-SiC(11(2)over-bar0)}, volume={255}, ISSN={["0169-4332"]}, DOI={10.1016/j.apsusc.2009.02.036}, abstractNote={The spatial origins of emissions from homoepitaxial 4H-SiC(112¯0) films have been investigated by cathodoluminescence, secondary ion mass spectrometry, and electron trajectory simulations. At 15 keV (300 K), the spectrum contained three peaks. The most intense peak corresponded (3.18 eV) to the nitrogen donor-to-valence band transition. The lesser two peaks at 2.94 eV and 2.75 eV involved aluminum and oxygen impurities, respectively; both impurities were determined to be in high concentrations in the film–substrate interfacial region. At 25 keV (300 K) the primary emission broadened into a band at ∼3.10 eV. Deconvolution revealed three peaks; the most intense emission was again the nitrogen donor-to-valence band transition. The remaining two peaks at 3.02 eV and 2.90 eV were consistent with transitions involving aluminum impurities. The former peak was not observed in the spectra obtained at lower electron beam energies and was correlated with the conduction band-to-aluminum acceptor level transition. Monte-Carlo simulations showed the origin of the 25 keV (300 K) spectrum was the film–substrate interface. An analysis of the aluminum impurity concentration in this region revealed that the cause of the 3.02 eV emission was a dramatic increase in the concentration of aluminum (3 × 1016 cm−3 to 1 × 1018 cm−3). The emissions comprising the 3.10 eV band were further investigated at 6 K and 25 keV. The difference in the intensity of the conduction band-to-aluminum acceptor level transition at 6 K and 300 K was attributed to thermal impurity ionization and the spike in the interfacial aluminum concentration previously described.}, number={13-14}, journal={APPLIED SURFACE SCIENCE}, author={Bishop, S. M. and Reynolds, C. L. and Molstad, J. C. and Stevie, F. A. and Barnhardt, D. E. and Davis, R. F.}, year={2009}, month={Apr}, pages={6535–6539} }
 @article{reitmeier_einfeldt_davis_zhang_fang_mahajan_2009, title={Sequential growths of AlN and GaN layers on as-polished 6H-SiC(0001) substrates}, volume={57}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2009.04.026}, abstractNote={Microstructures of surfaces and defects generated during initial and subsequent growths via metalorganic vapor-phase epitaxy of AlN(0001) films on 6H–SiC(0001) substrates and GaN(0001) films on AlN/SiC(0001) substrates have been investigated using atomic force microscopy and cross-sectional and plan-view transmission electron microscopy. Scratches present on the SiC surfaces did not appear to bias the nucleation of AlN. The lateral growth rate of AlN was greater than the vertical growth rate, leading to almost planar layers at 15 and 100 nm thicknesses. Partially coalesced islands were observed after nominally ∼15 nm of growth. Increasing the thickness to 100 nm resulted in complete island coalescence, formation of undulating films from the polishing scratches in the SiC substrate, a surface microstructure containing steps, terraces and small pits, and a reduced dislocation density relative to the 15 nm layers. The AlN/SiC interfaces contained steps and complex dislocation networks. GaN islands nucleated and grew on the AlN films. Complete coalescence of these islands occurred at thicknesses less than 100 nm. Dislocation density in the GaN films was reduced by increasing the thickness of either the AlN and or the GaN. Arguments are developed to account for these observations.}, number={14}, journal={ACTA MATERIALIA}, author={Reitmeier, Z. J. and Einfeldt, S. and Davis, R. F. and Zhang, Xinyu and Fang, Xialong and Mahajan, S.}, year={2009}, month={Aug}, pages={4001–4008} }
 @article{king_davis_nemanich_2008, title={Kinetics of Ga and In desorption from (7x7)Si(111) and (3x3)6H-SiC(0001) surfaces}, volume={602}, ISSN={["1879-2758"]}, DOI={10.1016/j.susc.2007.10.034}, abstractNote={The desorption characteristics of Ga and In on (7 × 7) Si(1 1 1) and (3 × 3) 6H-SiC(0 0 0 1) surfaces have been determined using temperature programmed desorption. Two peaks were observed for desorption of a 1.5 ± 0.25 monolayer of Ga from the latter surface. The peak at Tmax = 670 °C exhibited zeroth order kinetics; the activation energy and pre-exponential were determined to be 2.6 ± 0.1 eV and 6 × 1027 ± 0.5 atom/cm2 s, respectively. The peak at Tmax = 535 °C exhibited first order desorption kinetics with an activation energy and pre-exponential of 6.2 ± 0.3 eV and 7 × 1021 ± 2 s−1, respectively. In contrast, only zeroth order kinetics and a lower activation energy of 2.0 ± 0.1 eV were determined for desorption of a 1.5 ± 0.25 monolayer of Ga from (7 × 7) Si(1 1 1). The values of these results in tandem with those of related studies of desorption from Si and SiC surfaces indicate that the low and high temperature Ga peaks from SiC are due to desorption from either a wetting layer or adatom sites and from Ga islands, respectively. The difference in desorption activation energies for Ga on Si(1 1 1) and on 6H-SiC(0 0 0 1) surfaces is attributed to differences in lattice matching of Ga to these surfaces. By contrast, only multilayer desorption was observed for 4 ± 1 monolayer of In on SiC(0 0 0 1). The zeroth order desorption activation energy and pre-exponential were 2.4 ± 0.1 eV and 6 × 1027±0.5 atom/cm2 s; they are consistent with the heat of sublimation (2.45–2.5 eV) for liquid In.}, number={2}, journal={SURFACE SCIENCE}, author={King, S. W. and Davis, R. F. and Nemanich, R. J.}, year={2008}, month={Jan}, pages={405–415} }
 @misc{linthicum_gehrke_thomson_carlson_rajagopal_davis_2008, title={Pendeoepitaxial gallium nitride semiconductor layers on silicon carbide substrates}, volume={7,378,684}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Thomson, D. B. and Carlson, E. P. and Rajagopal, P. and Davis, R. F.}, year={2008} }
 @article{bishop_reynolds_liliental-weber_uprety_ebert_stevie_park_davis_2008, title={Sublimation growth of an in-situ-deposited layer in SiC chemical vapor deposition on 4H-SiC(1 1 (2)over-bar 0)}, volume={311}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2008.09.200}, abstractNote={Homoepitaxial growths of 4H-SiC(1 1 2¯ 0) epitaxial layers have been achieved using chemical vapor deposition from 1250 to 1600 °C and two process routes: (1) with and (2) without the addition of SiH4 and C2H4 to the growth ambient. An activation energy of 3.72 eV/atom (359 kJ/mol) was determined for the former route and associated with either reactions in the gas phase or the potential barrier associated with the temperature-dependent sticking coefficient. The activation energy for the latter route was 5.64 eV/atom (544 kJ/mol), which is consistent with published values for SiC sublimation epitaxy. Sublimation dominated the growth process at temperature ⩾1600 °C. The same effect resulted in the in-situ deposition of a thin film during the heating stage of route (1). At 1450 °C this layer was ∼100 nm thick and exhibited a specular surface microstructure with a roughness of 0.31 nm RMS. The in-situ-deposited layer was thus employed as an intermediate layer prior to epitaxial layer growth using route (1) at ∼1450 °C. Regions free of one- and two-dimensional defects were observed using cross-sectional transmission electron microscopy. Distinct interfaces were not observed between the substrate and the epitaxial layers.}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Bishop, S. M. and Reynolds, C. L., Jr. and Liliental-Weber, Z. and Uprety, Y. and Ebert, C. W. and Stevie, F. A. and Park, J. -S. and Davis, R. F.}, year={2008}, month={Dec}, pages={72–78} }
 @article{barabash_ice_roder_budai_liu_figge_einfeldt_hommel_davis_2007, title={Characterization of growth defects in thin GaN layers with X-ray microbeam}, volume={244}, ISSN={["1521-3951"]}, DOI={10.1002/pssb.200675113}, abstractNote={Abstract}, number={5}, journal={PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS}, author={Barabash, R. I. and Ice, G. E. and Roder, C. and Budai, J. and Liu, W. and Figge, S. and Einfeldt, S. and Hommel, D. and Davis, R. F.}, year={2007}, month={May}, pages={1735–1742} }
 @article{adekore_davis_barlage_2007, title={Electrical and optical properties of ZnO (000(1)over-bar) wafers implanted with argon}, volume={101}, number={2}, journal={Journal of Applied Physics}, author={Adekore, B. T. and Davis, R. F. and Barlage, D. W.}, year={2007} }
 @article{bishop_park_gu_wagner_reltmeier_batchelor_zakharov_liliental-weber_davis_2007, title={Growth evolution and pendeo-epitaxy of non-polar AlN and GaN thin films on 4H-SiC (11(2)over-bar0)}, volume={300}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2006.10.207}, abstractNote={The initial and subsequent stages of growth of AlN on 4H–SiC (1 1 2¯ 0) and GaN on AlN (1 1 2¯ 0) have been investigated using atomic force microscopy and X-ray photoelectron spectroscopy. The AlN nucleated and grew via the Stranski–Krastanov mode. Densely packed, [0 0 0 1]-oriented individual islands were observed at 10 nm. Additional deposition resulted in the gradual reorientation of the growth microstructure along the [1 1¯ 0 0]. GaN formed via the Volmer–Weber mode with rapid growth of islands along the [1 1¯ 0 0] to near surface coverage at a thickness of 2 nm. Continued deposition resulted in both faster vertical growth along [1 1 2¯ 0] relative to the lateral growth along [0 0 0 1] and a [1 1¯ 0 0]-oriented microstructure containing rows of GaN. Fully dense GaN films developed between 100 and 250 nm of growth, and the preferred in-plane orientation changed to [0 0 0 1]. Lateral growth of GaN films reduced the dislocation density from ∼4×1010 to ∼2×108 cm−2. The high concentration of stacking faults (∼106 cm−1) was also reduced two orders of magnitude.}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Bishop, S. M. and Park, J. -S. and Gu, J. and Wagner, B. P. and Reltmeier, Z. J. and Batchelor, D. A. and Zakharov, D. N. and Liliental-Weber, Z. and Davis, R. F.}, year={2007}, month={Mar}, pages={83–89} }
 @misc{zheleva_thomson_smith_linthicum_gehrke_davis_2007, title={Methods of fabricating gallium nitride semiconductor layers by lateral growth into trenches}, volume={7,195,993}, number={2007 Mar. 27}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Zheleva, T. and Thomson, D. B. and Smith, S. A. and Linthicum, K. J. and Gehrke, T. and Davis, R. F.}, year={2007} }
 @article{adekore_pierce_davisb_barlage_muth_2007, title={Nitrogen acceptors in bulk ZnO (000(1)over-bar)) substrates and homoepitaxial ZnO films}, volume={102}, ISSN={["1089-7550"]}, DOI={10.1063/1.2751097}, abstractNote={Bulk single crystals of unintentionally doped ZnO having charge carrier concentration, ND−NA values of ∼1017 cm−3 were implanted with N+ ions at dosages of 1015 and 1016 cm−2 at 95 keV to a depth of 150 nm. The resulting p−n structure having acceptor concentrations ranging from 1017 to 1018 cm−3 was compared with nitrogen doped homoepitaxial films with ∼8×1017 cm−3 acceptors. Photoluminescence spectra acquired at 8 K showed an increase in the peak for the neutral donor-bound to acceptor-bound transition at 3.210 eV with increasing annealing temperature, thermal activation of a unique donor to acceptor transition due to nitrogen at 3.067 and 3.057 eV for implanted and epitaxial films, respectively; and an increase in the intensity of the defect-related green band at selected temperatures. Electroluminescence measurements at 300 K revealed an ultraviolet band, direct band-to-band recombination at 3.34 eV, donor-acceptor pair recombinations at 3.19 and 3.0 eV, and recombination in the green region centered at 2.49 eV. Current-voltage characteristics of implanted and homoepitaxial p−n diodes were also determined.}, number={2}, journal={JOURNAL OF APPLIED PHYSICS}, author={Adekore, B. T. and Pierce, J. M. and Davisb, R. F. and Barlage, D. W. and Muth, J. F.}, year={2007}, month={Jul} }
 @misc{gehrke_linthicum_davis_2007, title={Pendeoepitaxial methods of fabricating gallium nitride semiconductor layers on sapphire substrates, and gallium nitride semiconductor structures fabricated thereby}, volume={7,217,641}, number={2007 May 15}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Gehrke, T. and Linthicum, K. J. and Davis, R. F.}, year={2007} }
 @article{chang_li_thomson_davis_2007, title={Phonon-assisted stimulated emission from pendeoepitaxy GaN stripes grown on 6H-SiC substrates}, volume={91}, number={5}, journal={Applied Physics Letters}, author={Chang, Y. C. and Li, Y. L. and Thomson, D. B. and Davis, R. F.}, year={2007} }
 @article{barabash_barabash_ice_roder_figge_einfeldt_2006, title={Characterization of crystallographic properties and defects via X-ray microdiffraction in GaN (0001) layers}, volume={203}, number={1}, journal={Physica Status Solidi. A, Applications and Materials Science}, author={Barabash, R. I. and Barabash, O. M. and Ice, G. E. and Roder, C. and Figge, S. and Einfeldt, S.}, year={2006}, pages={142–148} }
 @article{chang_kolbas_reitmeier_davis_2006, title={Effect of thermal annealing on the metastable optical properties of GaN thin films}, volume={24}, ISSN={["0734-2101"]}, DOI={10.1116/1.2209656}, abstractNote={The optical metastability in unintentionally doped GaN (0001) films grown on AlN∕SiC substrates has been investigated as a function of thermal annealing conditions using photoluminescence and optical microscopy. Annealing at 800°C for 48h in 1atm of flowing nitrogen produced no change in the metastability. Annealing at 800°C in ultrahigh vacuum for 48h eliminated the phenomenon. Exposure of the sample to ultraviolet light during the latter anneal reduced the time to eliminate the metastability. This phenomenon was restored by subsequently annealing in ammonia at 775°C for 3h. These results suggest that the presence and elimination of the optical metastability are related to the presence in and the elimination of hydrogen from the GaN.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Chang, Y. C. and Kolbas, R. M. and Reitmeier, Z. J. and Davis, R. F.}, year={2006}, pages={1051–1054} }
 @article{wagner_reitmeier_park_bachelor_zakharov_liliental-weber_davis_2006, title={Growth and characterization of pendeo-epitaxial GaN(11(2)over-bar0) on 4H-SiC(11(2)over-bar0) substrates}, volume={290}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2006.02.011}, abstractNote={Abstract Growth on AlN/4H–SiC ( 1 1 2 ¯ 0 ) substrates of coalesced, non-polar GaN ( 1 1 2 ¯ 0 ) films having volumes of material with reduced densities of dislocations and stacking faults has been achieved from etched stripes via the statistical and experimental determination of the effect of temperature and V/III ratio on the lateral and vertical growth rates of the GaN{0 0 0 1} faces combined with pendeo-epitaxy. AFM of the uncoalesced GaN(0 0 0 1) and GaN ( 0 0 0 1 ¯ ) vertical faces revealed growth steps with some steps terminating at dislocations on the former and a pitted surface without growth steps, indicative of decomposition, on the latter. Coalescence was achieved via (a) a two-step route and the parameters of (1) T = 1100 ° C and V / III = 1323 for 40 min and (2) 1020 °C and V / III = 660 for 40 min and (b) a one-step route that employed T = 1020 ° C and a V/III ratio = 660 for 6 h. The densities of dislocations in the GaN grown vertically over and laterally from the ( 1 1 2 ¯ 0 ) stripes were ∼4×10 10  cm −2 and ∼2×10 8  cm −2 , respectively; the densities of stacking fault in these volumes were ∼1×10 6  cm −1 and ∼2×10 4  cm −1 , respectively. The defects in the wing material were observed primarily at the bottom of the film where lateral growth of the GaN occurred from the AlN and the SiC. Plan view AFM also revealed different microstructures and a reduction in the RMS roughness values from 1.2 to 0.95 nm in these respective regions.}, number={2}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Wagner, BP and Reitmeier, ZJ and Park, JS and Bachelor, D and Zakharov, DN and Liliental-Weber, Z and Davis, RF}, year={2006}, month={May}, pages={504–512} }
 @article{park_reitmeier_fothergill_zhang_muth_davis_2006, title={Growth and fabrication of AlGaN-based ultraviolet light emitting diodes on 6H-SiC(0001) substrates and the effect of carrier-blocking layers on their emission characteristics}, volume={127}, ISSN={["0921-5107"]}, DOI={10.1016/j.mseb.2005.10.019}, abstractNote={Abstract Growth, fabrication, and the electrical and optical characterization of ultraviolet light emitting diodes and their components, including AlxGa1−xN films, quantum wells (QWs), and ohmic contacts, and the problems encountered in the process integration of these components have been investigated. Ni/Au ohmic contacts with specific contact resistivities of 2.2 × 10−4 and 2.0 × 10−2 Ω cm2 were achieved on annealed, Mg-doped ([Mg] ∼ 5 × 1019 cm−3), p-type GaN layers that had been cleaned in HCl at 85 °C and on the backside of the SiC substrates after annealing in nitrogen, respectively. The emission intensity of the diodes increased with an increase in the number of Al0.06Ga0.94N/Al0.10Ga0.90N QWs and with the use of Si-doped n-type barrier layers. The highest intensities of the principle emission at 353 nm were measured at all values of the injection current in the device with a p-type carrier-blocking layer at the top of the QWs; this device also exhibited the highest values of light output power. Growth of an n-type carrier-blocking layer at the bottom of the QWs had an adverse effect on their characteristics. A broad peak centered at ∼540 nm exhibited yellow luminescence and was present in the spectra acquired from all the devices. This peak is attributed to absorption of the ultraviolet emission by and re-emission from the p-GaN and/or to the luminescence from the AlGaN within QWs by current injection.}, number={2-3}, journal={MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, author={Park, JS and Reitmeier, ZJ and Fothergill, D and Zhang, XY and Muth, JF and Davis, RF}, year={2006}, month={Feb}, pages={169–179} }
 @article{balasubramanian_chang_mohammad_porter_salvador_dimaio_davis_2006, title={Growth and structural investigations of epitaxial hexagonal YMnO3 thin films deposited on wurtzite GaN(001) substrates}, volume={515}, ISSN={["1879-2731"]}, DOI={10.1016/j.tsf.2006.07.001}, abstractNote={Epitaxial hexagonal YMnO3 (h-YMnO3) films having sharp (00l) X-ray diffraction peaks were grown above 700 °C in 5 mTorr O2 via pulsed laser deposition both on as-received wurtzite GaN/AlN/6H-SiC(001) (w-GaN) substrates as well as on w-GaN surfaces that were etched in 50% HF solution. High-resolution transmission electron microscopy revealed an interfacial layer between film and the unetched substrate; this layer was absent in those samples wherein an etched substrate was used. However, the substrate treatment did not affect the epitaxial arrangement between the h-YMnO3 film and w-GaN substrate. The epitaxial relationships of the h-YMnO3 films with the w-GaN(001) substrate was determined via X-ray diffraction to be (001)YMnO3 ‖ (001)GaN : [11¯0]YMnO3 ‖ [110]GaN; in other words, the basal planes of the film and the substrate are aligned parallel to one another, as are the most densely packed directions in planes of the film and the substrate. Interestingly, this arrangement has a larger lattice mismatch than if the principal axes of the unit cells were aligned.}, number={4}, journal={THIN SOLID FILMS}, author={Balasubramanian, K. R. and Chang, Kai-Chieh and Mohammad, Feroz A. and Porter, Lisa M. and Salvador, Paul A. and DiMaio, Jeffrey and Davis, Robert F.}, year={2006}, month={Dec}, pages={1807–1813} }
 @article{barabash_ice_liu_roder_figge_einfeldt_hommel_katona_speck_denbaars_et al._2006, title={Mapping misorientation and crystallographic tilt in GaN layers via polychromatic microdiffraction}, volume={243}, ISSN={["0370-1972"]}, DOI={10.1002/pssb.200565442}, abstractNote={Abstract}, number={7}, journal={PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS}, author={Barabash, RI and Ice, GE and Liu, W and Roder, C and Figge, S and Einfeldt, S and Hommel, D and Katona, TM and Speck, JS and DenBaars, SP and et al.}, year={2006}, month={Jun}, pages={1508–1513} }
 @misc{linthicum_gehrke_davis_2006, title={Methods of fabricating gallium nitride semiconductor layers on substrates including non-gallium nitride posts, and gallium nitride semiconductor structures fabricated thereby}, volume={7,095,062}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Davis, R. F.}, year={2006} }
 @article{park_fothergill_wellenius_bishop_muth_davis_2006, title={Origins of parasitic emissions from 353 nm AlGaN-based ultraviolet light emitting diodes over SiC substrates}, volume={45}, ISSN={["0021-4922"]}, DOI={10.1143/jjap.45.4083}, abstractNote={The effects of p-GaN capping layer and p-type carrier-blocking layer on the occurrence of parasitic emissions from 353 nm AlGaN-based light emitting diodes (LEDs) have been investigated. LEDs without a p-type Al0.25Ga0.75N carrier-blocking layer showed a shoulder peak at ∼370 nm due to electron overflow into the p-Al0.10Ga0.90N cladding layer and subsequent electron–hole recombination in the acceptor levels. Broad emission between 380 and 450 nm from LEDs having a p-GaN capping layer was caused by luminescence at 420 nm from the p-GaN capping layer, which was optically pumped by 353 nm UV emission from the quantum wells. Broad, defect-related luminescence centered at ∼520 nm was emitted from the AlGaN layers within the quantum wells.}, number={5A}, journal={JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS}, author={Park, JS and Fothergill, DW and Wellenius, P and Bishop, SM and Muth, JF and Davis, RF}, year={2006}, month={May}, pages={4083–4086} }
 @article{lee_lee_hwang_reitmeier_davis_rogers_nuzzo_2005, title={A  printable form of single-crystalline gallium nitride for flexible optoelectronic systems}, volume={1}, number={12}, journal={Small (Weinheim An Der Bergstrasse, Germany)}, author={Lee, K. J. and Lee, J. and Hwang, H. D. and Reitmeier, Z. J. and Davis, R. F. and Rogers, J. A. and Nuzzo, R. G.}, year={2005}, pages={1164–1168} }
 @article{park_fothergill_zhang_reitmeier_muth_davis_2005, title={Effect of carrier blocking layers on the emission characteristics of AlGaN-based ultraviolet light emitting diodes}, volume={44}, ISSN={["0021-4922"]}, DOI={10.1143/jjap.44.7254}, abstractNote={ 
  AlGaN-based thin film heterostructures suitable for ultraviolet light emitting diodes have been grown and fabricated into working devices with and without p-type and n-type AlGaN carrier-blocking layers at the top and the bottom of the quantum wells, respectively. The principal emission from each device occurred at 353 nm. The highest intensities of this peak were measured at all values of the injection current in the device with a p-type carrier-blocking layer at the top of the quantum well; this device also exhibited the highest values of light output power. Growth of an n-type carrier-blocking layer at the bottom of the quantum wells had an adverse effect on the light emitting diode characteristics. A broad peak centered at ∼540 nm exhibited yellow luminescence and was present in the spectra acquired from all the devices. This peak is attributed to absorption of the UV emission by and re-emission from the p-GaN and/or to the luminescence from the AlGaN within quantum wells by current injection. The intensity of this peak increased and saturated by the same order of magnitude as the intensity of the UV emission at 353 nm. 
  }, number={10}, journal={JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS}, author={Park, JS and Fothergill, DW and Zhang, XY and Reitmeier, ZJ and Muth, JF and Davis, RF}, year={2005}, month={Oct}, pages={7254–7259} }
 @article{pierce_adekore_davis_stevie_2005, title={Growth of dense ZnO films via MOVPE on GaN(0001) epilayers using a low/high-temperature sequence}, volume={277}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2005.01.054}, abstractNote={Dense zinc oxide thin films have been achieved on GaN(0 0 0 1) epilayers via the repetition of an iterative sequence involving the growth at 480 °C of needles having a decreasing diameter as a function of height followed by the lateral growth from the sidewalls of these needles and coalescence of the growth fronts at 800 °C. Each sequence resulted in a contiguous layer having a thickness of approximately 200 nm. Diethylzinc and UHP oxygen were used as sources of zinc and atomic oxygen, respectively; UHP argon served as both the carrier and the diluent gas. The final growth surface of each densified film contained hexagonal depressions caused by growth among needles of different heights and growth pits that increased in number with an increase in film thickness. These microstructural features were manifest upon and affected the densities and magnitudes of similar features produced in subsequent layers. Triple-axis X-ray diffraction measurements revealed that the orientations of the crystallographic planes and directions within the films mimicked those of the underlying GaN substrate. Concentrations of carbon and hydrogen oscillated throughout the films due to their incorporation primarily within the lower and larger volumes of the needles during each low-temperature deposition of this microstructure.}, number={1-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Pierce, JM and Adekore, BT and Davis, RF and Stevie, FA}, year={2005}, month={Apr}, pages={345–351} }
 @article{pierce_adekore_davis_stevie_2005, title={Homoepitaxial growth of dense ZnO(0001) and ZnO (1120) films via MOVPE on selected ZnO substrates}, volume={283}, number={02-Jan}, journal={Journal of Crystal Growth}, author={Pierce, J. M. and Adekore, B. T. and Davis, R. F. and Stevie, F. A.}, year={2005}, pages={147–155} }
 @article{bai_huang_dudley_wagner_davis_wu_sutter_zhu_skromme_2005, title={Intersecting basal plane and prismatic stacking fault structures and their formation mechanisms in GaN}, volume={98}, number={6}, journal={Journal of Applied Physics}, author={Bai, J. and Huang, X. and Dudley, M. and Wagner, B. and Davis, R. F. and Wu, L. and Sutter, E. and Zhu, Y. and Skromme, B. J.}, year={2005} }
 @article{barabash_ice_liu_einfeldt_roskowski_davis_2005, title={Local strain, defects, and crystallographic tilt in GaN(0001) layers grown by maskless pendeo-epitaxy from x-ray microdiffraction}, volume={97}, number={1}, journal={Journal of Applied Physics}, author={Barabash, R. I. and Ice, G. E. and Liu, W. and Einfeldt, S. and Roskowski, A. M. and Davis, R. F.}, year={2005} }
 @misc{linthicum_gehrke_davis_2005, title={Methods of fabricating gallium nitride semiconductor layers on substrates including non-gallium nitride posts}, volume={6,864,160}, number={2005 Mar. 8}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Davis, R. F.}, year={2005} }
 @article{kroger_einfeldt_chierchia_hommel_reitmeier_davis_liu_2005, title={On the microstructure of AlxGa1-xN layers grown on 6H-SiC(0001) substrates}, volume={97}, number={8}, journal={Journal of Applied Physics}, author={Kroger, R. and Einfeldt, S. and Chierchia, R. and Hommel, D. and Reitmeier, Z. J. and Davis, R. F. and Liu, Q. K. K.}, year={2005} }
 @article{egerton_sood_singh_puri_davis_pierce_look_steiner_2005, title={P-type doping utilizing nitrogen and Mn doping of ZnO using MOCVD for ultraviolet lasers and spintronic applications}, volume={34}, ISSN={["1543-186X"]}, DOI={10.1007/s11664-005-0048-y}, number={6}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Egerton, EJ and Sood, AK and Singh, R and Puri, YR and Davis, RF and Pierce, J and Look, DC and Steiner, T}, year={2005}, month={Jun}, pages={949–952} }
 @article{hartman_naniwae_petrich_nemanich_davis_2005, title={Photo-electron emission and atomic force microscopies of the hydrogen etched 6H-SiC(0001) surface and the initial growth of GaN and AlN}, volume={242}, ISSN={["0169-4332"]}, DOI={10.1016/j.apsusc.2004.09.021}, abstractNote={Photo-emission electron microscopy (PEEM) and atomic force microscopy (AFM) have been used to characterize the surfaces of hydrogen etched 6H-SiC(0 0 0 1) wafers and the microstructure of the initial stages of growth of GaN and AlN on these surfaces via molecular beam epitaxy. The PEEM images were obtained using a free electron laser as the photon source. A stepped structure was evident in these images of the surfaces etched at 1600–1700 °C for 15 min. Comparison with the AFM images revealed that emission was occurring from the intersection of the steps and the terraces. Images of the initial stages of deposition of the GaN thin films at 700 and 800 °C revealed three-dimensional island growth. The degree of coalescence of these films was dependent upon the step structure: regions containing steps having unit cell height exhibited complete or nearly complete coalescence; regions containing steps with half unit cell height showed voids in the films parallel to the steps. PEEM of the initial stages of growth of AlN revealed immediate nucleation and rapid coalescence during deposition at 900 °C, except in areas on the substrate surface containing steps having half unit cell height. Incomplete coalescence and pits were also observed in the latter areas.}, number={3-4}, journal={APPLIED SURFACE SCIENCE}, author={Hartman, JD and Naniwae, K and Petrich, C and Nemanich, R and Davis, RF}, year={2005}, month={Apr}, pages={428–436} }
 @article{mecouch_wagner_reitmeier_davis_pandarinath_rodriguez_nemanich_2005, title={Preparation and characterization of atomically clean, stoichlometric surfaces of AIN(0001)}, volume={23}, ISSN={["0734-2101"]}, DOI={10.1116/1.1830497}, abstractNote={In situ exposure of the (0001) surface of AlN thin films to flowing ammonia at 1120 °C and 10−4Torr removes oxygen∕hydroxide and hydrocarbon species below the detectable limits of x-ray photoelectron spectroscopy and decreases the Al∕N ratio from 1.3 to 1.0. The positions of the Al2p and the N1s core level peaks acquired from the cleaned surfaces were 75.0±0.1eV and 398.2±0.1eV, respectively, which were similar to the values determined for the as-loaded samples. The cleaning process left unchanged the (1×1) low energy electron diffraction pattern, the step-and-terrace microstructure, and the root mean square roughness values observed for the surfaces of the as-loaded samples; i.e., the surface structure and microstructure were not changed by the high-temperature exposure to ammonia at low pressures. Vacuum annealing under 10−7Torr at 1175 °C for 15 min removed all detectable hydrocarbons; however, it did not remove the oxygen∕hydroxide species.}, number={1}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Mecouch, WJ and Wagner, BP and Reitmeier, ZJ and Davis, RF and Pandarinath, C and Rodriguez, BJ and Nemanich, RJ}, year={2005}, pages={72–77} }
 @misc{zheleva_thomson_smith_linthicum_gehrke_davis_2005, title={Second gallium nitride layers that extend into trenches in first gallium nitride layers}, volume={6,897,483}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Zheleva, T. and Thomson, D. B. and Smith, S. A. and Linthicum, K. J. and Gehrke, T. and Davis, R. F.}, year={2005} }
 @article{huang_bai_dudley_wagner_davis_zhu_2005, title={Step-controlled strain relaxation in the vicinal surface epitaxy of nitrides}, volume={95}, number={8}, journal={Physical Review Letters}, author={Huang, X. R. and Bai, J. and Dudley, M. and Wagner, B. and Davis, R. F. and Zhu, Y.}, year={2005} }
 @article{zakharov_liliental-weber_wagner_reitmeier_preble_davis_2005, title={Structural TEM study of nonpolar a-plane gallium nitride grown on (1120) 4H-SiC by organometallic vapor phase epitaxy}, volume={71}, number={23}, journal={Physical Review. B, Condensed Matter and Materials Physics}, author={Zakharov, D. N. and Liliental-Weber, Z. and Wagner, B. and Reitmeier, Z. J. and Preble, E. A. and Davis, R. F.}, year={2005} }
 @article{bai_dudley_chen_skromme_wagner_davis_chowdhury_dupuis_2005, title={Structural defects and luminescence features in heteroepitaxial GaN grown on on-axis and misoriented substrates}, volume={97}, number={11}, journal={Journal of Applied Physics}, author={Bai, J. and Dudley, M. and Chen, L. and Skromme, B. J. and Wagner, B. and Davis, R. F. and Chowdhury, U. and Dupuis, R. D.}, year={2005} }
 @article{coppa_fulton_kiesel_davis_pandarinath_burnette_nemanich_smith_2005, title={Structural, microstructural, and electrical properties of gold films and Schottky contacts on remote plasma-cleaned, n-type ZnO{0001} surfaces}, volume={97}, ISSN={["1089-7550"]}, DOI={10.1063/1.1898436}, abstractNote={Current–voltage measurements of Au contacts deposited on ex situ cleaned, n-type ZnO(0001) [(0001¯)] surfaces showed reverse bias leakage current densities of ∼0.01(∼0.1)A∕cm2 at 4.6 (3.75) V reverse bias and ideality factors >2 (both surfaces) before sharp, permanent breakdown (soft breakdown). This behavior was due primarily to the presence of (1.6–2.0)±0.1[(0.7–2.6)±0.1] monolayers (ML) of hydroxide, which forms an electron accumulation layer and increases the surface conductivity. In situ remote plasma cleaning of the (0001) [(0001¯)] surfaces using a 20vol%O2∕80vol%He mixture for the optimized temperatures, times, and pressure of 550±20°C(525±20°C), 60 (30) min, and 0.050 Torr reduced the thickness of the hydroxide layer to ∼0.4±0.1ML and completely eliminated all detectable hydrocarbon contamination. Subsequent cooling of both surfaces in the plasma ambient resulted in the chemisorption of oxygen and a change from 0.2 eV of downward band bending for samples cooled in vacuum to 0.3 eV of upward band bending indicative of the formation of a depletion layer of lower surface conductivity. Cooling in either ambient produced stoichiometric ZnO{0001} surfaces having an ordered crystallography as well as a step-and-terrace microstructure on the (0001¯) surface; the (0001) surface was without distinctive features. Sequentially deposited, unpatterned Au films, and presumably the rectifying gold contacts, initially grew on both surfaces cooled in the plasma ambient via the formation of islands that subsequently coalesced, as indicated by calculations from x-ray photoelectron spectroscopy data and confirmed by transmission electron microscopy. Calculations from the current–voltage data of the best contacts revealed barrier heights on the (0001) [(0001¯)] surfaces of 0.71±0.05(0.60±0.05)eV, a saturation current density of (4±0.5)×10−6A∕cm2(2.0±0.5×10−4A∕cm2), a lower value of n=1.17±0.05(1.03±0.05), a significantly lower leakage current density of ∼1.0×10−4A∕cm2(∼91×10−9A∕cm2) at 8.5 (7.0) V reverse bias prior to sharp, permanent breakdown (soft breakdown). All measured barrier heights were lower than the predicted Schottky–Mott value of 1.0 eV, indicating that the interface structure and the associated interface states affect the Schottky barrier. However, the constancy in the full width at half maximum of the core levels for Zn 2p(1.9±0.1eV) and O 1s(1.5±0.1eV), before and after sequential in situ Au depositions, indicated an abrupt, unreacted Au∕ZnO(0001) interface. Transmission electron microscopy confirmed the abruptness of an epitaxial interface. Annealing the contacts on the (0001) surface to 80±5 and 150±5°C resulted in decreases in the ideality factors to 1.12±0.05 and 1.09±0.05 and increases in saturation current density to 9.05 and 4.34μA∕cm2, the barrier height to 0.82±0.5 and 0.79±0.5eV, and in the leakage current densities to ∼2×10−3A∕cm2 at 6 V and ∼20×10−3A∕cm2 at 7 V, respectively.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Coppa, BJ and Fulton, CC and Kiesel, SM and Davis, RF and Pandarinath, C and Burnette, JE and Nemanich, RJ and Smith, DJ}, year={2005}, month={May} }
 @article{matlock_zvanut_wang_dimaio_davis_van nostrand_henry_koleske_wickenden_2005, title={The effects of oxygen, nitrogen, and hydrogen annealing on Mg acceptors in GaN as monitored by electron paramagnetic resonance spectroscopy}, volume={34}, ISSN={["1543-186X"]}, DOI={10.1007/s11664-005-0177-3}, number={1}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Matlock, DM and Zvanut, ME and Wang, HY and Dimaio, JR and Davis, RF and Van Nostrand, JE and Henry, RL and Koleske, D and Wickenden, A}, year={2005}, month={Jan}, pages={34–39} }
 @article{yang_prater_liu_glass_davis_2005, title={The formation of epitaxial hexagonal boron nitride on nickel substrates}, volume={34}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-005-0165-7}, number={12}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Yang, PC and Prater, JT and Liu, W and Glass, JT and Davis, RF}, year={2005}, month={Dec}, pages={1558–1564} }
 @article{barabash_ice_liu_einfeldt_hommel_roskowski_davis_2005, title={White X-ray microbeam analysis of strain and crystallographic tilt in GaN layers grown by maskless pendeoepitaxy}, volume={202}, number={5}, journal={Physica Status Solidi. A, Applications and Materials Science}, author={Barabash, R. I. and Ice, G. E. and Liu, W. and Einfeldt, S. and Hommel, D. and Roskowski, A. M. and Davis, R. F.}, year={2005}, pages={732–738} }
 @article{smith_mclean_smith_miraglia_roskowski_davis_2004, title={Growth and characterization of ZnO thin films on GaN epilayers}, volume={33}, ISSN={["1543-186X"]}, DOI={10.1007/s11664-004-0249-9}, number={7}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Smith, TP and McLean, HA and Smith, DJ and Miraglia, PQ and Roskowski, AM and Davis, RF}, year={2004}, month={Jul}, pages={826–832} }
 @inbook{bishop_preble_hallin_henry_storasta_jacobson_wagner_reitmeier_janzen_davis_2004, title={Growth of homoepitaxial films on 4H-SiC(1120) and 8 degrees off-axis 4H-SiC(0001) substrates and their characterization}, volume={457-460}, booktitle={Silicon carbide and related materials 2003: ICSCRM2003: Proceedings of the 10th International Conference on Silicon Carbide and Related Materials 2003, Lyon, France, October 5-10, 2003}, publisher={Utikon-Zurich, Switzerland: Trans Tech Publications}, author={Bishop, S. M. and Preble, E. A. and Hallin, C. and Henry, A. and Storasta, L. and Jacobson, H. and Wagner, B. P. and Reitmeier, Z. and Janzen, E. and Davis, R. F.}, editor={R. Madar, J. Camassel and Blanquet, E.Editors}, year={2004}, pages={221–224} }
 @article{paskova_valcheva_paskov_monemar_roskowski_davis_beaumont_gibart_2004, title={HVPE-GaN: comparison of emission properties and microstructure of films grown on different laterally overgrown templates}, volume={13}, ISSN={0925-9635}, url={http://dx.doi.org/10.1016/j.diamond.2003.10.072}, DOI={10.1016/j.diamond.2003.10.072}, abstractNote={We report on a comparative study of defect and emission distributions in thick hydride vapor phase epitaxial (HVPE) GaN films grown on two different patterned template structures separately produced by multi-step procedures using metalorganic vapor phase epitaxy (MOVPE). The observed differences in the microstructures and emission distributions at the early stages of the growth in both cases were related to the change of the dominating growth mode sequence and point defects incorporation. Both template structures were found to favor formation of voids in the coalescence regions, which leads to a partial strain relaxation and allows overgrowth of thicker films without cracks.}, number={4-8}, journal={Diamond and Related Materials}, publisher={Elsevier BV}, author={Paskova, T. and Valcheva, E. and Paskov, P.P. and Monemar, B. and Roskowski, A.M. and Davis, R.F. and Beaumont, B. and Gibart, P.}, year={2004}, month={Apr}, pages={1125–1129} }
 @article{smith_mclean_smith_davis_2004, title={Homoepitaxial growth of (0001)- and (000(1)over-bar)-oriented ZnO thin films via metalorganic vapor-phase epitaxy and their characterization}, volume={265}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2004.02.096}, abstractNote={Homoepitaxial ZnO films have been grown via metalorganic vapor-phase epitaxy on O- and Zn-terminated basal-plane-oriented ZnO substrates. Maps of on-axis X-ray rocking curves obtained over 2-in-diameter ZnO{0 0 0 1} wafers, diced from boules produced by vapor phase transport, revealed well-defined areas that ranged from <50 to >1050 arcsec FWHM, indicating the presence of tilted domains. This macrostructure was manifested in all the homoepitaxial ZnO films deposited on these wafers. The films grown on O-terminated ZnO surfaces were initially dense. However, they changed to a textured polycrystalline microstructure after ≈100 nm and possessed a surface roughness of 7.3 nm. By contrast, the films grown on the Zn-terminated surface under the same conditions were fully dense, without texture and appeared to be monocrystalline with a significantly improved surface roughness of 3.4 nm. Cross-sectional transmission electron microscopy of the wafers revealed high densities of edge dislocations and stacking faults with associated Frank partial dislocations.}, number={3-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Smith, TP and McLean, H and Smith, DJ and Davis, RF}, year={2004}, month={May}, pages={390–398} }
 @article{coppa_fulton_hartlieb_davis_rodriguez_shields_nemanich_2004, title={In situ cleaning and characterization of oxygen- and zinc-terminated, n-type, ZnO{0001} surfaces}, volume={95}, ISSN={["1089-7550"]}, DOI={10.1063/1.1695596}, abstractNote={A layer containing an average of 1.0 monolayer (ML) of adventitious carbon and averages of 1.5 ML and 1.9 ML of hydroxide was determined to be present on the respective O-terminated (0001̄) and Zn-terminated (0001) surfaces of ZnO. A diffuse low-energy electron diffraction pattern was obtained from both surfaces. In situ cleaning procedures were developed and their efficacy evaluated in terms of the concentrations of residual hydrocarbons and hydroxide and the crystallography, microstructure, and electronic structure of these surfaces. Annealing ZnO(0001̄) in pure oxygen at 600–650 °C±20 °C reduced but did not eliminate all of the detectable hydrocarbon contamination. Annealing for 15 min in pure O2 at 700 °C and 0.100±0.001 Torr caused desorption of both the hydrocarbons and the hydroxide constituents to concentrations below the detection limits (∼0.03 ML=∼0.3 at. %) of our x-ray photoelectron spectroscopy instrument. However, thermal decomposition degraded the surface microstructure. Exposure of the ZnO(0001̄) surface to a remote plasma having an optimized 20% O2/80% He mixture for the optimized time, temperature, and pressure of 30 min, 525 °C, and 0.050 Torr, respectively, resulted in the desorption of all detectable hydrocarbon species. Approximately 0.4 ML of hydroxide remained. The plasma-cleaned surface possessed an ordered crystallography and a step-and-terrace microstructure and was stoichiometric with nearly flat electronic bands. A 0.5 eV change in band bending was attributed to the significant reduction in the thickness of an accumulation layer associated with the hydroxide. The hydroxide was more tightly bound to the ZnO(0001) surface; this effect increased the optimal temperature and time of the plasma cleaning process for this surface to 550 °C and 60 min, respectively, at 0.050 Torr. Similar changes were achieved in the structural, chemical, and electronic properties of this surface; however, the microstructure only increased slightly in roughness and was without distinctive features.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Coppa, BJ and Fulton, CC and Hartlieb, PJ and Davis, RF and Rodriguez, BJ and Shields, BJ and Nemanich, RJ}, year={2004}, month={May}, pages={5856–5864} }
 @article{reitmeier_park_mecouch_davis_2004, title={In situ cleaning of GaN(0001) surfaces in a metalorganic vapor phase epitaxy environment}, volume={22}, number={5}, journal={Journal of Vacuum Science & Technology. A, Vacuum, Surfaces, and Films}, author={Reitmeier, Z. J. and Park, J. S. and Mecouch, W. J. and Davis, R. F.}, year={2004}, pages={2077–2082} }
 @misc{gehrke_linthicum_davis_2004, title={Pendeoepitaxial methods of fabricating gallium nitride semiconductor layers on sapphire substrates, and gallium nitride semiconductor structures fabricated thereby}, volume={6,686,261}, number={2004 Feb. 3}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Gehrke, T. and Linthicum, K. J. and Davis, R. F.}, year={2004} }
 @article{grenko_reynolds_schlesser_bachmann_rietmeier_davis_sitar_2004, title={Selective etching of GaN from AlGaN/GaN and AlN/GaN structures}, volume={9}, DOI={10.1557/s1092578300000405}, abstractNote={Thick GaN layers as well as AlGaN/GaN and AlN/GaN heterostructures grown by metalorganic vapor phase epitaxy have been photoelectrochemically (PEC) etched in various dilute electrolytes, and bandgap-selective etching has been demonstrated in heterostructures. This result is a significant step forward in the fabrication of group III-nitride devices and one-dimensional photonic bandgap (PBG) structures in the deep UV. Based on initial results from thick GaN layers, a method was developed to achieve self-stopping selective etching of thin GaN layers in AlGaN/GaN and AlN/GaN heterostructures. Selective PEC etching requires the use of a suitable light source with photon energies larger than the bandgap of GaN, but smaller than that of AlGaN or AlN, thus enabling selective hole generation in the GaN layers to be etched. Additionally, it is imperative to use an electrolyte that supports PEC etching of GaN without chemically etching AlGaN or AlN.}, number={5}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Grenko, J. A. and Reynolds, C. L. and Schlesser, R. and Bachmann, K. and Rietmeier, Z. and Davis, R. F. and Sitar, Z.}, year={2004} }
 @article{smith_lamb_mcginnis_davis_2004, title={Surface-roughness correlations in homoepitaxial growth of GaN(0001) films by NH3 supersonic jet epitaxy}, volume={96}, ISSN={["1089-7550"]}, DOI={10.1063/1.1785869}, abstractNote={Homoepitaxial GaN films were grown on GaN(0001)∕6H-SiC substrates by NH3 supersonic jet epitaxy at 750°C using a constant Ga flux of 2.9×1014cm−2s−1 and varying the NH3 flux and average kinetic energy. Atomic force microscopy (AFM), scanning electron microscopy, and in situ reflection high-energy electron diffraction evidence an abrupt transition from quasi-two-dimensional basal-plane growth to three-dimensional faceted growth at approximately 1∕2 of the maximum Ga-limited growth rate, irrespective of NH3 kinetic energy. Topographical scaling analysis of the AFM images reveals that the smooth and rough GaN(0001) films have static scaling exponents (α) of 0.88±0.05 and 1.10±0.06, respectively. The dynamic scaling exponent (β) for rough films is approximately 0.25. A comparison of these scaling exponents with predictions based on continuum growth models indicates that competition between surface diffusion and stochastic roughening governs the evolution of surface morphology during GaN growth.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Smith, NA and Lamb, HH and McGinnis, AJ and Davis, RF}, year={2004}, month={Oct}, pages={4556–4562} }
 @article{cook_fulton_mecouch_davis_lucovsky_nemanich_2003, title={Band offset measurements of the GaN (0001)/HfO2 interface}, volume={94}, DOI={10.1063/1.1618374}, number={11}, journal={Journal of Applied Physics}, author={Cook, T. E. and Fulton, C. C. and Mecouch, W. J. and Davis, R. F. and Lucovsky, G. and Nemanich, R. J.}, year={2003}, pages={7155–7158} }
 @article{cook_fulton_mecouch_davis_lucovsky_nemanich_2003, title={Band offset measurements of the Si3N4/GaN (0001) interface}, volume={94}, ISSN={["0021-8979"]}, DOI={10.1063/1.1601314}, abstractNote={X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy were used to measure electronic states as Si3N4 was deposited on clean GaN (0001) surfaces. The n-type (2×1018) and p-type (1×1017) GaN surfaces were atomically cleaned in NH3 at 860 °C, and the n-and p-type surfaces showed upward band bending of ∼0.2±0.1 eV and downward band bending of 1.1±0.1 eV, respectively, both with an electron affinity of 3.1±0.1 eV. Layers of Si (∼0.2 nm) were deposited on the clean GaN and nitrided using an electron cyclotron resonance N2 plasma at 300 °C and subsequently annealed at 650 °C for densification into a Si3N4 film. Surface analysis was performed after each step in the process, and yielded a valence band offset of 0.5±0.1 eV. Both interfaces exhibited type II band alignment where the valence band maximum of GaN lies below that of the Si3N4 valence band. The conduction band offset was deduced to be 2.4±0.1 eV, and a change of the interface dipole of 1.1±0.1 eV was observed for Si3N4/GaN interface formation.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Cook, TE and Fulton, CC and Mecouch, WJ and Davis, RF and Lucovsky, G and Nemanich, RJ}, year={2003}, month={Sep}, pages={3949–3954} }
 @article{hartman_roskowski_reitmeier_tracy_davis_nemanich_2003, title={Characterization of hydrogen etched 6H-SiC(0001) substrates and subsequently grown AlN films}, volume={21}, ISSN={["0734-2101"]}, DOI={10.1116/1.1539080}, abstractNote={Wafers of n-type, 6H–SiC(0001) with (ND–NA)=(5.1–7.5)×1017 and 2.5×1018 were etched in a flowing 25%H2/75%He mixture within the range of 1500–1640 °C at 1 atm. Equilibrium thermodynamic calculations indicated that the presence of atomic hydrogen is necessary to achieve etching of SiC. Atomic force microscopy, optical microscopy, and low energy electron diffraction of the etched surface revealed a faceted surface morphology with unit cell and half unit cell high steps and a 1×1 reconstruction. The latter sample also exhibited a much larger number of hexagonal pits on the surface. Annealing the etched samples under ultrahigh vacuum (UHV) at 1030 °C for 15 min resulted in (1) a reduction of the surface oxygen and adventitious hydrocarbons below the detection limit of Auger electron spectroscopy, (2) a (√3×√3)R30° reconstructed surface and (3) a Si-to-C peak-to-peak height ratio of 1.2. By contrast, using a chemical vapor cleaning (CVC) process consisting of an exposure to 3000 Langmuir (L) of silane at 1030 °C for 10 min under UHV conditions resulted in a (3×3) surface reconstruction, a Si-to-C ratio of 3.9, and islands of excess silicon. Continued annealing of the latter material for an additional 10 min at 1030 °C resulted in a (1×1) LEED pattern with a diffuse ring. Films of AlN grown via MOCVD at a sample platter temperature of 1274 °C for 15 min on hydrogen etched wafers having a doping concentration of 8.7×1017 cm−3 and cleaned via annealing had a rms roughness value of ≈0.4 nm.}, number={2}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Hartman, JD and Roskowski, AM and Reitmeier, ZJ and Tracy, KM and Davis, RF and Nemanich, RJ}, year={2003}, pages={394–400} }
 @article{preble_miraglia_roskowski_vetter_dudley_davis_2003, title={Domain structures in 6H-SiC wafers and their effect on the microstructures of GaN films grown on AlN and Al0.2Ga0.8N buffer layers}, volume={258}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(03)01515-X}, abstractNote={Silicon carbide wafers contain domains with varying sizes and degrees of tilt. The present research has shown that this microstructure is mimicked in GaN films deposited on AlN-containing buffer layers and that it masks most variations in the FWHM of the X-ray rocking curves of the former. The shape and FWHM in the GaN curves are determined both by domain tilting and dislocation broadening; the latter was dominant in areas of reduced tilt. Analyses of the on- and off-axis X-ray data acquired from these regions of lower tilt revealed the marked effect of the higher density of edge dislocations on broadening. This effect decreased with increasing GaN thickness due to dislocation annihilation. The densities of edge dislocations in GaN films deposited at 1010°C on pitted, less pitted and very smooth AlN layers of the same thickness grown at 1010°C, 1130°C and 1220°C, respectively, were lowest and highest in those films grown on the last two respective layers. Additional studies showed that GaN films grow on Al0.2Ga0.8N layers via step-flow and possess a lower edge dislocation density than films grown via the Stranski–Krastanov mode on AlN because of the reduced misfit and the absence of boundaries between coalesced islands.}, number={1-2}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Preble, EA and Miraglia, PQ and Roskowski, AM and Vetter, WM and Dudley, M and Davis, RF}, year={2003}, month={Oct}, pages={75–83} }
 @article{tracy_hartlieb_einfeldt_davis_hurt_nemanich_2003, title={Electrical and chemical characterization of the Schottky barrier formed between clean n-GaN(0001) surfaces and Pt, Au, and Ag}, volume={94}, ISSN={["0021-8979"]}, DOI={10.1063/1.1598630}, abstractNote={Platinum, gold, and silver formed abrupt, unreacted, smooth, and epitaxial metal–semiconductor interfaces when deposited from the vapor onto clean, n-type GaN(0001) films. The Schottky barrier heights, determined from data acquired using x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, capacitance–voltage, and current–voltage measurements agreed to within the experimental error for each contact metal and had the values of 1.2±0.1, 0.9±0.1, and 0.6±0.1 eV for Pt, Au, and Ag, respectively. The band bending and the electron affinity at the clean n-GaN surface were 0.3±0.1 and 3.1±0.1 eV, respectively. The barrier height is proportional to the metal work function, indicating that the Fermi level is not pinned at the GaN surface. However, discrepancies to the Schottky–Mott model were found as evidenced by a proportionality factor of 0.44 between the work function of the metal and the resulting Schottky barrier height. The sum of these discrepancies constitute the interface dipole contributions to the Schottky barrier height which were measured to be ∼1.4, 1.3, and 0.7 eV for Pt, Au, and Ag, respectively.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Tracy, KM and Hartlieb, PJ and Einfeldt, S and Davis, RF and Hurt, EH and Nemanich, RJ}, year={2003}, month={Sep}, pages={3939–3948} }
 @article{collazo_schlesser_roskowski_miraglia_davis_sitar_2003, title={Electron energy distribution during high-field transport in AlN}, volume={93}, ISSN={["0021-8979"]}, DOI={10.1063/1.1543633}, abstractNote={The energy distribution of electrons transported through intrinsic AlN heteroepitaxial films grown on SiC was directly measured as a function of applied field and AlN film thickness. Following the transport, electrons were extracted into vacuum through a semitransparent Au electrode and their energy distribution was measured using an electron spectrometer. Transport through films thicker than 95 nm at an applied field between 200 and 350 kV/cm occurred as steady-state hot electron transport following a Maxwellian energy distribution with a characteristic carrier temperature. At higher fields (470 kV/cm), intervalley scattering was evidenced by a multicomponent energy distribution featuring a second peak at the energy position of the first satellite valley. Velocity overshoot was observed in films thinner than 95 nm and at fields greater than 550 kV/cm. In this case, a symmetric energy distribution centered at an energy above the conduction band minimum was measured, indicating that the drift component of the electron velocity was on the order of the “thermal” component. A transient transport length of less than 80 nm was deduced from these observations.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Collazo, R and Schlesser, R and Roskowski, A and Miraglia, P and Davis, RF and Sitar, Z}, year={2003}, month={Mar}, pages={2765–2771} }
 @article{smith_mecouch_miraglia_roskowski_hartlieb_davis_2003, title={Evolution and growth of ZnO thin films on GaN(0001) epilayers via metalorganic vapor phase epitaxy}, volume={257}, ISSN={["1873-5002"]}, DOI={10.1016/S0022-0248(03)01469-6}, abstractNote={Zinc oxide thin films have been grown via metalorganic vapor phase epitaxy at 450°C and 250 Torr total pressure on O-terminated areas and micro-regions of native oxide formed on GaN(0 0 0 1) epilayers during exposure to the oxygen reactant. Analyses of the Ga3d core level spectra acquired from films grown for progressively longer times and comparisons of these data with both thermodynamic models of growth processes and associated atomic force micrographs revealed that the ZnO nucleated and grew via the Stranski–Krastanov mode. Considerations of (1) differences in surface energetics of the polar (0 0 0 1) surfaces of ZnO and GaN and that of the Ga-based oxide as well as (2) the relatively low stress generated by the moderate lattice mismatches in the a-axis lattice parameters of these compounds supported the observed growth mode. The shifts in the position of the Ga3d core level with increasing deposition time and decreasing peak intensity were caused by surface charging and increasing sampling volumes of the Ga-based oxide as well as the growing ZnO layer. The island/ocean morphology of the Ga-based oxide controlled the morphology of the initial ZnO layer, which, in turn controlled the locations and the morphologies of the subsequently nucleated ZnO islands. Scanning electron microscopy of thicker ZnO films revealed a highly textured microstructure.}, number={3-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Smith, TP and Mecouch, WJ and Miraglia, PQ and Roskowski, AM and Hartlieb, PJ and Davis, RF}, year={2003}, month={Oct}, pages={255–262} }
 @article{usov_parikh_kudriavtsev_asomoza_reitmeier_davis_2003, title={GaN evaporation and enhanced diffusion of Ar during high-temperature ion implantation}, volume={93}, ISSN={["1089-7550"]}, DOI={10.1063/1.1564271}, abstractNote={GaN films were implanted with 150 keV Ar+ at temperatures up to 1100 °C to a dose of 3×1015 cm−2. Concentration profiles of Ar were measured by secondary ion mass spectroscopy and depth distributions of ion-induced damage were estimated from Rutherford backscattering/channeling spectra. No redistribution of Ar atoms was detected up to 700 °C. At 1000 °C a deep penetrating diffusion tail and a shift of the Ar peak to the surface were observed. At temperatures higher than 800 °C shift of the damage peak to the surface was also observed. We attributed the shift of the Ar peak and the damage peaks to evaporation of thin layer of GaN during high-temperature implantation and estimated its temperature dependence.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Usov, I and Parikh, N and Kudriavtsev, Y and Asomoza, R and Reitmeier, Z and Davis, R}, year={2003}, month={May}, pages={5140–5142} }
 @article{davis_einfeldt_preble_roskowski_reitmeier_miraglia_2003, title={Gallium nitride and related materials: challenges in materials processing}, volume={51}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2003.08.005}, abstractNote={Boules and large wafers of the III-Nitrides of AlN, GaN and InN having a low density of dislocations are not available. As such, essentially all nitride films and device structures are grown on either sapphire or silicon carbide substrates containing a previously deposited buffer layer of GaN, AlN or AlGaN. These films grow via complex thermodynamically- and kinetically-controlled mechanisms and contain significant residual stresses and densities of defects that affect the properties of all optoelectronic and microelectronic devices produced in this materials system. It is the purpose of this paper to describe the challenges presented by the growth of these heteroepitaxial films and some of the recent results of research to understand the complex relationships between film growth, and stress and defect generation as well as the reduction in these mechanical and microstructural problems. Films of GaN grow on AlN/SiC substrates via the formation of a 1–1.5 nm thick wetting layer and the subsequent growth and coalescence of islands. These films are biaxially stressed. Increasing their thickness causes a gradual change in their average strain and their local strain from compression to tension due to the mismatch in lattice parameters between GaN and AlN and the mismatch in the coefficients of thermal expansion between GaN and SiC. A portion of the compressive stress is relieved within the first 20 nm due to the formation of misfit dislocations. Copious threading dislocations are also generated. Additional microstructural problems are presented by the SiC substrates that contain domains with varying size and tilt that are mimicked in the GaN films and that mask most variations in the FWHM of their X-ray rocking curves. Reduction in both the residual stresses and the dislocation density has been achieved via lateral overgrowth techniques.}, number={19}, journal={ACTA MATERIALIA}, author={Davis, RF and Einfeldt, S and Preble, EA and Roskowski, AM and Reitmeier, ZJ and Miraglia, PQ}, year={2003}, month={Nov}, pages={5961–5979} }
 @misc{davis_nam_2003, title={Gallium nitride semiconductor structure including laterally offset patterned layers}, volume={6,608,327}, number={2003 Aug. 19}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Davis, R. F. and Nam, O.-H.}, year={2003} }
 @misc{linthicum_gehrke_davis_2003, title={Gallium nitride semiconductor structures fabricated by pendeoepitaxial methods of fabricating gallium nitride semiconductor layers on weak posts}, volume={6,586,778}, number={2003 July 1}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Davis, R. F.}, year={2003} }
 @misc{davis_nam_zheleva_bremser_2003, title={Gallium nitride semiconductor structures including lateral gallium nitride layers}, volume={6,570,192}, number={2003 May 27}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Davis, R. F. and Nam, O.-H. and Zheleva, T. and Bremser, M. D.}, year={2003} }
 @article{coppa_davis_nemanich_2003, title={Gold Schottky contacts on oxygen plasma-treated, n-type ZnO(000(1)over-bar)}, volume={82}, ISSN={["0003-6951"]}, DOI={10.1063/1.1536264}, abstractNote={Reverse bias current–voltage measurements of ∼100-μm-diameter gold Schottky contacts deposited on as-received, n-type ZnO(0001̄) wafers and those exposed for 30 min to a remote 20% O2/80% He plasma at 525±20 °C and cooled either in vacuum from 425 °C or the unignited plasma gas have been determined. Plasma cleaning resulted in highly ordered, stoichiometric, and smooth surfaces. Contacts on as-received material showed μA leakage currents and ideality factors >2. Contacts on plasma-cleaned wafers cooled in vacuum showed ∼36±1 nA leakage current to −4 V, a barrier height of 0.67±0.05 eV, and an ideality factor of 1.86±0.05. Cooling in the unignited plasma gas coupled with a 30 s exposure to the plasma at room temperature resulted in decreases in these parameters to ∼20 pA to −7 V, 0.60±0.05 eV, and 1.03±0.05, respectively. Differences in the measured and theoretical barrier heights indicate interface states. (0001) and (0001̄) are used in this letter to designate the polar zinc- and oxygen-terminated surfaces, respectively.}, number={3}, journal={APPLIED PHYSICS LETTERS}, author={Coppa, BJ and Davis, RF and Nemanich, RJ}, year={2003}, month={Jan}, pages={400–402} }
 @article{miraglia_preble_roskowski_einfeldt_davis_2003, title={Helical-type surface defects in GaN thin films epitaxially grown on GaN templates at reduced temperatures}, volume={253}, ISSN={["1873-5002"]}, DOI={10.1016/S0022-0248(03)00970-9}, abstractNote={Surface pits in the form of v-shaped defects and resulting surface roughening, previously associated solely with InGaN films, were observed and investigated using atomic force microscopy on GaN films grown at 780°C via metalorganic vapor phase epitaxy on conventionally and pendeo-epitaxially deposited GaN thin film templates. The density of the v-shaped defects was similar to the density of threading dislocations of ∼3×109 cm−2 (that originate from the heteroepitaxial interface between the GaN template layer and the SiC substrate). Moreover, the v-defect density was diminished with decreases in the dislocation density via increases in the template layer thickness or the use of pendeo-epitaxial seed layers. A concomitant reduction in the full-width half-maxima of the X-ray rocking curves was also observed. A qualitative model is presented that describes the formation of v-shaped defects as a result of interactions between the movement of surface steps, screw-type dislocation cores, and clusters of atoms on the terraces that form under conditions of high surface undercooling.}, number={1-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Miraglia, PQ and Preble, EA and Roskowski, AM and Einfeldt, S and Davis, RF}, year={2003}, month={Jun}, pages={16–25} }
 @article{miraglia_preble_roskowski_einfeldt_lim_liliental-weber_davis_2003, title={Helical-type surface defects in InGaN thin films epitaxially grown on GaN templates at reduced temperatures}, volume={437}, ISSN={["1879-2731"]}, DOI={10.1016/S0040-6090(03)00611-4}, abstractNote={Abstract The surface morphologies of InGaN films grown at 780 °C by metalorganic vapor phase epitaxy were determined using atomic force microscopy. A qualitative model was developed to explain the observed instabilities in the step morphology of these films, namely, the formation of hillocks and v-defects that give rise to surface roughening. V-defects, observed at a surface density greater than 2×10 8 /cm 2 , are a result of interactions between moving surface steps, cores of screw-type dislocations, and two-dimensional islands of atoms that form on the terraces during growth at high surface undercooling. A delay in the formation of v-defects in InGaN to a nominal thickness of 10 nm was observed and associated with the ammonia partial pressure and the interactions between steps associated with hillock islands and cores of screw-type dislocations. Hillock formation was attributed to a transition in the thermodynamic mode of film growth, as three-dimensional islands nucleated on the cores of screw-type dislocations at a density of 2×10 8 /cm 2 . Explanations for the foregoing observations are based on growth model theory previously developed by Burton, Cabrera and Frank and on changes in the surface kinetics with temperature, In composition, and gas phase composition.}, number={1-2}, journal={THIN SOLID FILMS}, author={Miraglia, PQ and Preble, EA and Roskowski, AM and Einfeldt, S and Lim, SH and Liliental-Weber, Z and Davis, RF}, year={2003}, month={Aug}, pages={140–149} }
 @article{jessen_fitch_gillespie_via_moser_yannuzzi_crespo_sewell_dettmer_jenkins_et al._2003, title={High performance 0.14 mu m gate-length AlGaN/GaN power HEMTs on SiC}, volume={24}, ISSN={["0741-3106"]}, DOI={10.1109/LED.2003.818816}, abstractNote={High electron mobility transistors (HEMTs) were fabricated from AlGaN/GaN on semi-insulating SiC substrates with excellent performance and high yield. The devices had 0.14 /spl mu/m T-gates with a total width of 300 /spl mu/m. Extrinsic, unpassivated peak performance values for these HEMTs include transconductance of 338 mS/mm, maximum drain current of 1481 mA/mm, unity current gain cutoff frequency of 91 GHz, and maximum frequency of oscillation of 122 GHz. Saturated CW power measurements of these devices at 10 GHz result in 4.6 W/mm with PAE at 46% when optimized for power and 3.0 W/mm with PAE at 65% when optimized for efficiency.}, number={11}, journal={IEEE ELECTRON DEVICE LETTERS}, author={Jessen, GH and Fitch, RC and Gillespie, JK and Via, GD and Moser, NA and Yannuzzi, MJ and Crespo, A and Sewell, JS and Dettmer, RW and Jenkins, TJ and et al.}, year={2003}, month={Nov}, pages={677–679} }
 @article{cook_fulton_mecouch_tracy_davis_hurt_lucovsky_nemanich_2003, title={Measurement of the band offsets of SiO2 on clean n- and p-type GaN(0001)}, volume={93}, ISSN={["0021-8979"]}, DOI={10.1063/1.1559424}, abstractNote={The band alignment at the SiO2-GaN interface is important for passivation of high voltage devices and for gate insulator applications. X-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy have been used to observe the interface electronic states as SiO2 was deposited on clean GaN(0001) surfaces. The substrates, grown by metallorganic chemical vapor deposition, were n- (1×1017) and p-type (2×1018) GaN on 6H-SiC(0001) with an AlN(0001) buffer layer. The GaN surfaces were atomically cleaned via an 860 °C anneal in an NH3 atmosphere. For the clean surfaces, n-type GaN showed upward band bending of 0.3±0.1 eV, while p-type GaN showed downward band bending of 1.3±0.1 eV. The electron affinity for n- and p-type GaN was measured to be 2.9±0.1 and 3.2±0.1 eV, respectively. To avoid oxidizing the GaN, layers of Si were deposited on the clean GaN surface via ultrahigh vacuum e-beam deposition, and the Si was oxidized at 300 °C by a remote O2 plasma. The substrates were annealed at 650 °C for densification of the SiO2 films. Surface analysis techniques were performed after each step in the process, and yielded a valence band offset of 2.0±0.2 eV and a conduction band offset of 3.6±0.2 eV for the GaN-SiO2 interface for both p- and n-type samples. Interface dipoles of 1.8 and 1.5 eV were deduced for the GaN-SiO2 interface for the n- and p-type surfaces, respectively.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Cook, TE and Fulton, CC and Mecouch, WJ and Tracy, KM and Davis, RF and Hurt, EH and Lucovsky, G and Nemanich, RJ}, year={2003}, month={Apr}, pages={3995–4004} }
 @misc{linthicum_gehrke_davis_thomson_tracy_2003, title={Methods of fabricating gallium nitride microelectronic layers on silicon layers}, volume={6,602,764}, number={2003 Aug. 5}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Davis, R. F. and Thomson, D. B. and Tracy, K. M.}, year={2003} }
 @misc{davis_nam_zheleva_bremser_2003, title={Methods of fabricating gallium nitride semiconductor layers by lateral overgrowth}, volume={6,602,763}, number={2003 Aug. 5}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Davis, R. F. and Nam, O.-H. and Zheleva, T. and Bremser, M. D.}, year={2003} }
 @misc{linthicum_gehrke_davis_2003, title={Methods of fabricating gallium nitride semiconductor layers on substrates including non-gallium nitride posts, and gallium nitride semiconductor structures fabricated thereby}, volume={6,621,148}, number={2003 Sept. 16}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Davis, R. F.}, year={2003} }
 @article{schwarz_schuck_mason_grober_roskowski_einfeldt_davis_2003, title={Microscopic mapping of strain relaxation in uncoalesced pendeoepitaxial GaN on SiC}, volume={67}, number={4}, journal={Physical Review. B, Condensed Matter and Materials Physics}, author={Schwarz, U. T. and Schuck, P. J. and Mason, M. D. and Grober, R. D. and Roskowski, A. M. and Einfeldt, S. and Davis, R. F.}, year={2003}, pages={045321–1} }
 @misc{gehrke_linthicum_davis_2003, title={Pendeoepitaxial methods of fabricating gallium nitride semiconductor layers on sapphire substrates}, volume={6,521,514}, number={2003 Feb. 18}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Gehrke, T. and Linthicum, K. J. and Davis, R. F.}, year={2003} }
 @misc{gehrke_linthicum_davis_2003, title={Pendeoepitaxial methods of fabricating gallium nitride semiconductor layers on sapphire substrates, and gallium nitride semiconductor structures fabricated thereby}, volume={6,545,300}, number={2003 Apr. 8}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Gehrke, T. and Linthicum, K. J. and Davis, R. F.}, year={2003} }
 @article{tracy_mecouch_davis_nemanich_2003, title={Preparation and characterization of atomically clean, stoichiometric surfaces of n- and p-type GaN(0001)}, volume={94}, ISSN={["1089-7550"]}, DOI={10.1063/1.1596369}, abstractNote={It is demonstrated that in situ exposure of the (0001) surface of n- and p-type GaN thin films to flowing ammonia at 860 °C and 10−4 Torr removes hydrocarbon and oxygen/hydroxide species below the detectable limits of x-ray and ultraviolet photoelectron spectroscopies (UPS) and decreases the Ga/N ratio from 1.3 to 1.0. Additional indications of the efficacy of this ammonia-based chemical vapor cleaning (CVC) process were the shifts in the Ga 3d and the N 1s core level positions from the as-loaded to the CVC surfaces of the n-type samples from 21.0±0.1 to 20.6±0.1 eV and from 398.3±0.1 to 398.0±0.1 eV, respectively, and the change in the UPS measured low energy spectrum turn on from 3.9±0.1 (as-loaded samples) to 3.0±0.1 eV (cleaned samples) below the Fermi level. Analogous changes in the p-type samples were from 19.6±0.1 to 18.9±0.1 eV and from 397.1±0.1 to 396.3±0.1 eV for the Ga 3d and the N 1s core levels, and from 3.0±0.1 to 1.1±0.1 eV for the UPS valence band maximum (VBM). The VBM values of the CVC samples indicate band bending of ∼0.3 eV upward on n type and ∼0.8 eV downward on p type. Electron affinities of 2.8±0.1 and 2.6±0.1 eV were determined for the clean n-type and p-type surfaces, respectively. Irrespective of doping, the CVC process left unchanged the (1×1) low energy diffraction pattern, the terraced microstructure, and the root mean square roughness observed for the surfaces of the as-loaded samples, i.e., the surface microstructure was not damaged during the high temperature exposure to ammonia at low pressure.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Tracy, KM and Mecouch, WJ and Davis, RF and Nemanich, RJ}, year={2003}, month={Sep}, pages={3163–3172} }
 @article{hartlieb_roskowski_davis_platow_nemanich_2003, title={Response to "Comment on 'Pd growth and subsequent Schottky barrier formation on chemical vapor cleaned p-type GaN surfaces' [J. Appl. Phys. 91, 732 (2002)]"}, volume={93}, ISSN={["0021-8979"]}, DOI={10.1063/1.1542911}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Hartlieb, PJ and Roskowski, A and Davis, RF and Platow, W and Nemanich, RJ}, year={2003}, month={Mar}, pages={3679–3679} }
 @article{mcginnis_thomson_banks_preble_davis_lamb_2003, title={Supersonic jet epitaxy of gallium nitride using triethylgallium and ammonia}, volume={21}, ISSN={["0734-2101"]}, DOI={10.1116/1.1532736}, abstractNote={Gallium nitride (GaN) films were grown on GaN(0001)/AlN/6H–SiC composite substrates at 700–780 °C by supersonic jet epitaxy using triethylgallium (TEG) and NH3. TEG was seeded in He and N2 supersonic free jets to obtain kinetic energies of ∼2.1 and ∼0.5 eV, respectively, and NH3 was supplied from a variable leak valve. Higher TEG beam intensities (by about a factor of 5) were obtained by seeding in He. In situ reflection high-energy electron diffraction indicated a transition from three-dimensional to two-dimensional (2D) growth between 730 and 750 °C for films grown using TEG seeded in He and a constant NH3/TEG flux ratio. Ex situ atomic force microscopy of films grown at 730 and 750 °C revealed smooth surfaces comprised of quasi-2D islands with irregular perimeters. Cross-sectional transmission electron microscopy evidenced that the film grown at 750 °C was homoepitaxial α-GaN with a high density of planar lattice defects. Secondary ion mass spectrometry detected high residual carbon concentrations in the films. The GaN growth rate at 750 °C was found to depend on TEG flux and NH3 pressure in a manner consistent with Langmuir–Hinshelwood kinetics. Films grown under NH3-rich conditions were faceted and microscopically rough, whereas nonfaceted, basal-plane growth was observed under Ga-rich conditions. The first-order dependence of growth rate on TEG flux under NH3-rich conditions was used to estimate Ga incorporation efficiencies for high- and low-energy TEG beams. The Ga incorporation efficiency is lower for high-energy TEG beams, consistent with a decrease in the sticking coefficient for dissociative chemisorption.}, number={1}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={McGinnis, AJ and Thomson, D and Banks, A and Preble, E and Davis, RF and Lamb, HH}, year={2003}, pages={294–301} }
 @article{einfeldt_reitmeier_davis_2003, title={Surface morphology and strain of GaN layers grown using 6H-SiC(0001) substrates with different buffer layers}, volume={253}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(03)01039-X}, abstractNote={The evolution of both the surface morphology and the strain in GaN layers grown by metalorganic vapor phase epitaxy on either AlN or AlxGa1−xN (x≈0.15) buffer layers previously deposited on 6H-SiC(0 0 0 1) substrates has been investigated by varying the layer thickness from one GaN bilayer to 4μm. The GaN surfaces initially contained pits and undulations; the latter became smoother with continued growth. The growth of a 1–1.5 nm thick and continuous wetting layer and the subsequent formation of islands within the undulations are characteristic of the Stranski–Krastanov growth mode observed for the growth of GaN on AlN. The islands coalesced within the first 10 nm. Instead, a step-flow growth mode was observed for the growth of GaN on AlGaN. Increasing the thickness of the GaN grown on either AlN or AlGaN caused these biaxially stressed layers to gradually change their state of stress from compression to tension with regard to both their average strain and their local strain along the growth direction. The compressive and tensile stress components are attributed to the mismatch in lattice parameters between the GaN and the buffer layer and the mismatch in the coefficients of thermal expansion between GaN and SiC, respectively. A portion of the compressive stress is relieved within the first 20 nm of GaN grown on AlN buffer layer. The relief of the remaining stress follows an exponential dependence on the thickness of the GaN layer with values for the characteristic decay length of 0.24 and 0.64μm for the AlN and AlGaN buffer layer, respectively. The relaxation mechanism is discussed in terms of the formation of misfit dislocations via surface undulations.}, number={1-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Einfeldt, S and Reitmeier, ZJ and Davis, RF}, year={2003}, month={Jun}, pages={129–141} }
 @article{preble_mclean_kiesel_miraglia_albrecht_davis_2002, title={Application of Nomarski interference contrast microscopy as a thickness monitor in the preparation of transparent, SiG-based, cross-sectional TEM samples}, volume={92}, ISSN={["0304-3991"]}, DOI={10.1016/S0304-3991(02)00142-0}, abstractNote={Reflected light optical microscopy using a Nomarski prism and a differential interference contrast filter have been employed in concert to achieve a technique that provides an accurate color reference for thickness during the dimpling and ion milling of transparent transmission electron microscopy samples of 6H-SiC(000 1) wafers. The samples had thin films of AIN, GaN, and Au deposited on the SiC substrate. A sequence of variously colored primary and secondary interference bands was observed when the SiC was thinner than 20 microm using an optical microscope. The color bands were correlated with the TEM sample thickness as measured via scanning electron microscopy. The interference contrast was used to provide an indication of the dimpling rate, the ion milling rate, and also the most probable location of perforation, which are useful to reduce sample breakage. The application of pressure during the initial cross-sectional preparation reduced the separation of the two halves of the sample sandwich and resulted in increased shielding of the film surface from ion milling damage.}, number={3-4}, journal={ULTRAMICROSCOPY}, author={Preble, EA and McLean, HA and Kiesel, SM and Miraglia, P and Albrecht, M and Davis, RF}, year={2002}, month={Aug}, pages={265–271} }
 @article{hartlieb_roskowski_davis_nemanich_2002, title={Chemical, electrical, and structural properties of Ni/Au contacts on chemical vapor cleaned p-type GaN}, volume={91}, ISSN={["1089-7550"]}, DOI={10.1063/1.1471578}, abstractNote={Chemical vapor cleaned, Mg-doped, p-type GaN(0001) surfaces and Ni/Au contacts deposited on these surfaces have been studied using several characterization techniques. Stoichiometric surfaces without detectable carbon and an 87% reduction in the surface oxygen to 2±1 at. % were achieved. The binding energies of the Ga 3d and N 1s core level photoelectron peaks were reduced by 0.5±0.1 eV following the chemical vapor clean. The band bending at the clean surface was measured to be 0.8±0.1 eV. As-deposited Ni/Au contacts on chemical vapor cleaned surfaces exhibited significantly less rectification in the low voltage region (<2 V) compared to identical contact structures on conventional HCl treated surfaces. The specific contact resistance of these contacts deposited on chemical vapor cleaned surfaces and subsequently annealed at 450 °C for 30 seconds was 3±2 Ω cm2. Improved ohmic behavior and a specific contact resistance of 4±2 Ω cm2 was obtained for contacts deposited on HCl treated surfaces and annealed using the same schedule. The formation of Au:Ga and Au:Ni solid solutions was observed for contacts on HCl treated surfaces following the 450 °C anneal. There were significantly less interfacial reactions for annealed contacts on chemical vapor cleaned surfaces. The values of specific contact resistance, sheet resistance, and transfer length of the annealed contacts deposited on both chemical vapor cleaned and HCl treated surfaces and measured from room temperature to 140 °C did not change during three successive thermal cycles within this range.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Hartlieb, PJ and Roskowski, A and Davis, RF and Nemanich, RJ}, year={2002}, month={Jun}, pages={9151–9160} }
 @article{schuck_grober_roskowski_einfeldt_davis_2002, title={Cross-sectional imaging of pendeo-epitaxial GaN using continuous-wave two-photon microphotoluminescence}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1506948}, abstractNote={A technique utilizing continuous-wave two-photon absorption has been developed for optically sectioning and imaging deep into GaN structures. Imaging at depths greater than 20 μm below the surface of a coalesced pendeo-epitaxial GaN sample is demonstrated. Free and donor-bound excitonic emission in this sample appears to originate at the surface, acceptor-bound exciton transitions are strongest in the top bulk portion of the sample, and subgap luminescence is most intense deep in the sample. The depth resolution of the imaging system is measured to be 1.75 μm near the GaN surface.}, number={11}, journal={APPLIED PHYSICS LETTERS}, author={Schuck, PJ and Grober, RD and Roskowski, AM and Einfeldt, S and Davis, RF}, year={2002}, month={Sep}, pages={1984–1986} }
 @article{usov_parikh_thomson_davis_2002, title={Effect of implantation temperature on damage accumulation in Ar-implanted GaN}, volume={7}, number={9}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Usov, I. and Parikh, N. and Thomson, D. B. and Davis, R. F.}, year={2002}, pages={9–1} }
 @article{preble_tracy_kiesel_mclean_miraglia_nemanich_davis_albrecht_smith_2002, title={Electrical, structural and microstructural characteristics of as-deposited and annealed Pt and Au contacts on chemical-vapor-cleaned GaN thin films}, volume={91}, ISSN={["0021-8979"]}, DOI={10.1063/1.1432127}, abstractNote={Schottky contacts of Pt(111) and Au(111) were deposited on chemical-vapor-cleaned, n-type GaN(0001) thin films. The growth mode of the deposition, as determined by x-ray photoelectron spectroscopy analysis, followed the two-dimensional Frank–van der Merwe growth model. The resulting as-deposited metal films were monocrystalline and epitaxial with a (111)//(0002) relationship with the GaN. Selected samples were annealed for three minutes at 400 °C, 600 °C or 800 °C. The rectifying behavior of both contacts degraded at 400 °C; they became ohmic after annealing at 600 °C (Au) or 800 °C (Pt). High-resolution transmission electron micrographs revealed reactions at the metal/GaN interfaces for the higher temperature samples. X-ray diffraction results revealed an unidentified phase in the Pt sample annealed at 800 °C. A decrease in the room temperature in-plane (111) lattice constant for both metals, ranging from −0.1% to −0.5%, was observed as the annealing temperature was increased from 400 to 800 °C. This plastic deformation was caused by tensile stresses along the [111] direction that exceeded the yield strength as a result of the large differences in the coefficients of thermal expansion between the metal contacts and the GaN film.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={Preble, EA and Tracy, KM and Kiesel, S and McLean, H and Miraglia, PQ and Nemanich, RJ and Davis, RF and Albrecht, M and Smith, DJ}, year={2002}, month={Feb}, pages={2133–2137} }
 @article{chang_cai_johnson_muth_kolbas_reitmeier_einfeldt_davis_2002, title={Electron-beam-induced optical memory effects in GaN}, volume={80}, ISSN={["0003-6951"]}, DOI={10.1063/1.1469222}, abstractNote={Metastable effects in unintentionally doped GaN films grown on SiC substrates have been investigated using cathodoluminescence (CL). Memory effect patterns produced optically are observed in CL images. An electron beam can also produce memory effect patterns and the resulting changes in the luminescence spectra are quite similar for either optical or electron-beam-induced patterns. CL spectra reveal that the yellow luminescence at 2.2 eV increases significantly with little change in the band-edge emission in both cases. Samples that do not exhibit optically induced memory effects are also investigated and do not exhibit electron-beam-induced patterns, either. Monochromatic CL images at 540 and 365 nm confirm the similarity of optically and electron-beam-induced memory effects based on changes in luminescence spectra.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Chang, YC and Cai, AL and Johnson, MAL and Muth, JF and Kolbas, RM and Reitmeier, ZJ and Einfeldt, S and Davis, RF}, year={2002}, month={Apr}, pages={2675–2677} }
 @article{davis_roskowski_preble_speck_heying_freitas_glaser_carlos_2002, title={Gallium nitride materials - Progress, status, and potential roadblocks}, volume={90}, ISSN={["1558-2256"]}, DOI={10.1109/JPROC.2002.1021564}, abstractNote={Metal-organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) are the principal techniques for the growth and n-type (Si) and p-type (Mg) doping of III-nitride thin films on sapphire and silicon carbide substrates as well as previously grown GaN films. Lateral and pendeoepitaxy via MOVPE reduce significantly the dislocation density and residual strain in GaN and AlGaN films. However tilt and coalescence boundaries are produced in the laterally growing material. Very high electron mobilities in the nitrides have been realized in radio-frequency plasma-assisted MBE GaN films and in two-dimensional electron gases in the AlGaN/GaN system grown on MOVPE-derived GaN substrates at the crossover from the intermediate growth regime to the droplet regime. State-of-the-art Mg doping profiles and transport properties have been achieved in MBE-derived p-type GaN. The Mg-memory effect, and heterogeneous growth, substrate uniformity, and flux control are significant challenges for MOVPE and MBE, respectively. Photoluminescence (PL) of MOVPE-derived unintentionally doped (UID) heteroepitaxial GaN films show sharp lines near 3.478 eV due to recombination processes associated with the annihilation of free-excitons (FEs) and excitons bound to a neutral shallow donor (D/spl deg/X).}, number={6}, journal={PROCEEDINGS OF THE IEEE}, author={Davis, RF and Roskowski, AM and Preble, EA and Speck, JS and Heying, B and Freitas, JA and Glaser, ER and Carlos, WE}, year={2002}, month={Jun}, pages={993–1005} }
 @article{shin_arkun_thomson_miraglia_preble_schlesser_wolter_sitar_davis_2002, title={Growth and decomposition of bulk GaN: role of the ammonia/nitrogen ratio}, volume={236}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(02)00825-4}, abstractNote={Gallium nitride crystals grown via vapor-phase transport processes that incorporate ammonia as the only source of nitrogen below atmospheric pressures experience significant surface roughening and the eventual cessation of growth. Investigations of these phenomena in this research, and in the context of the discovery of a non-ceasing process route to larger GaN crystals, showed that the RMS values of the surface roughness of single crystal GaN (0 0 0 1) films exposed to pure ammonia flowing at 60 sccm for 2 h at 1130°C increased from the as-received value of 3.7–6.8 nm, 21.4 and 32.6 nm at 100, 430 and 760 Torr, respectively. Quadrupole mass spectrometry revealed that the concentrations of H2 and N2 measurably increased at pressures above 400 Torr. The primary reason for the increased roughness above 430 Torr was the enhanced etching of GaN via reaction with atomic and molecular hydrogen derived from the dissociation of the ammonia. At lower pressures, the decomposition of the GaN via the formation and evaporation of N2 and Ga increased in importance relative to etching for enhancing surface roughness. Dilution with nitrogen reduced the amount of hydrogen generated from the dissociation of the ammonia. The GaN surface annealed at 1130°C and 430 Torr in ammonia diluted with 33 vol% N2 maintained the smoothest surface with a nominal RMS value of 10.4 nm. Mixtures with higher and lower percentages of N2 showed enhanced roughness under the same conditions. Use of this optimum gas mixture also allowed the seeded growth of a 1.5×1.5×2.0 mm3 GaN crystal and a 2.3×1.8×0.3 mm3 thick platelet with neither observable decomposition nor cessation of the growth over periods of 36 and 48 h, respectively.}, number={4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Shin, H and Arkun, E and Thomson, DB and Miraglia, P and Preble, E and Schlesser, R and Wolter, S and Sitar, Z and Davis, RF}, year={2002}, month={Mar}, pages={529–537} }
 @article{shin_thomson_schlesser_davis_sitar_2002, title={High temperature nucleation and growth of GaN crystals from the vapor phase}, volume={241}, ISSN={["1873-5002"]}, DOI={10.1016/S0022-0248(02)01290-3}, abstractNote={A vapor phase growth process involving the reaction of Ga vapor and ammonia has been used to grow needle- and platelet-shaped single crystals of GaN at 1130°C. Introduction of the NH3 only at high temperatures reduced the nucleation density, minimized the amount of GaN crust on the Ga source and resulted in larger crystals. A processing map has been constructed with respect to ammonia flow rate and total pressure at 1130°C to achieve control of growth in different crystallographic directions. Platelet growth of GaN was favored using low V/III ratios achieved via low ammonia flow rates and/or low total ammonia pressures and/or an increase in the Ga source temperature. Crystals with aspect ratios c/a<1 were obtained at 1130°C, 430 Torr, and 25–75 sccm of ammonia. Raman spectroscopy revealed that the best platelets were grown at 1130°C using ammonia flow rates of 60 sccm and a Ga source temperature of 1260°C. Seeded growth from previously grown needles and platelets at lateral and vertical rates of ∼25 and ∼10 μm/h, respectively, was achieved using these growth parameters.}, number={4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Shin, H and Thomson, DB and Schlesser, R and Davis, RF and Sitar, Z}, year={2002}, month={Jun}, pages={404–415} }
 @misc{gehrke_linthicum_davis_thomson_2002, title={High temperature pendeoepitaxial methods of fabricating gallium nitride semiconductor layers on sapphire substrates}, volume={6,489,221}, number={2002 Dec. 3}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Gehrke, T. and Linthicum, K. J. and Davis, R. F. and Thomson, D. B.}, year={2002} }
 @article{roskowski_preble_einfeldt_miraglia_davis_2002, title={Investigations regarding the maskless pendeo-epitaxial growth of GaN films prior to coalescence}, volume={38}, ISSN={["0018-9197"]}, DOI={10.1109/JQE.2002.801005}, abstractNote={Pendeo-epitaxy employs lateral growth from etched seed forms to achieve a marked reduction in dislocation density in a material. In this research, high-resolution X-ray diffraction and atomic force microscopy of GaN stripes and the laterally grown wings confirmed transmission electron microscopy results regarding the reduction in dislocations in the latter regions. Micro-Raman and X-ray diffraction measurements showed the wings to be tilted /spl les/0.15/spl deg/ due to tensile stresses in the stripes induced primarily by the mismatch in the coefficients of thermal expansion between the GaN stripe and the SiC substrate. A strong, low-temperature D/spl deg/X peak at /spl ap/3.466 eV with a FWHM of /spl les/300 /spl mu/eV was measured in the wing material by micro-photoluminescence. Films grown at 1020/spl deg/C exhibited similar vertical [0001] and lateral [112~0] growth rates. Increasing the growth temperature increased the latter due to the higher thermal stability of the (112~0) GaN and initiated growth of spiral hillocks on the (0001) surface of the stripes. The latter were due to adatom diffusion to heterogeneous steps previously nucleated at the intersections of pure screw or mixed dislocations. The (112~0) surface was atomically smooth under all growth conditions with a root mean square roughness value of 0.17 nm.}, number={8}, journal={IEEE JOURNAL OF QUANTUM ELECTRONICS}, author={Roskowski, AM and Preble, EA and Einfeldt, S and Miraglia, PM and Davis, RF}, year={2002}, month={Aug}, pages={1006–1016} }
 @article{roskowski_preble_einfeldt_miraglia_davis_2002, title={Maskless pendeo-epitaxial growth of GaN films}, volume={31}, ISSN={["1543-186X"]}, DOI={10.1007/s11664-002-0095-6}, number={5}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Roskowski, AM and Preble, EA and Einfeldt, S and Miraglia, PM and Davis, RF}, year={2002}, month={May}, pages={421–428} }
 @misc{linthicum_gehrke_davis_2002, title={Methods of fabricating gallium nitride semiconductor layers on substrates including non-gallium nitride posts}, volume={6,403,451}, number={2002 Jun. 11}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Davis, R. F.}, year={2002} }
 @misc{gehrke_linthicum_davis_2002, title={Methods of forming compound semiconductor layers using spaced trench arrays and semiconductor substrates formed thereby}, volume={6,486,042}, number={2002 Nov. 26}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Gehrke, T. and Linthicum, K. J. and Davis, R. F.}, year={2002} }
 @article{hartlieb_roskowski_davis_platow_nemanich_2002, title={Pd growth and subsequent Schottky barrier formation on chemical vapor cleaned p-type GaN surfaces}, volume={91}, ISSN={["1089-7550"]}, DOI={10.1063/1.1424060}, abstractNote={Characterization of chemical vapor cleaned, Mg-doped, p-type GaN(0001) surfaces and Pd contacts sequentially deposited on these surfaces has been conducted using x-ray and ultraviolet photoelectron spectroscopies and low-energy electron diffraction. The band bending and the electron affinity at the cleaned p-GaN surface were 1.4±0.1 eV and 3.1±0.1 eV, respectively. A previously unidentified band of surface states was observed at ∼1.0 eV below the Fermi level on this surface. The Pd grew epitaxially on the cleaned surface in a layer-by-layer mode and formed an abrupt, unreacted metal–semiconductor interface. The induced Fermi level movement with Pd deposition has been attributed to a complex interaction between extrinsic and intrinsic surface states as well as metal induced gap states. The final Schottky barrier height at the Pd/p-GaN interface was 1.3±0.1 eV; the interface dipole contribution was 0.4±0.1 eV.}, number={2}, journal={JOURNAL OF APPLIED PHYSICS}, author={Hartlieb, PJ and Roskowski, A and Davis, RF and Platow, W and Nemanich, RJ}, year={2002}, month={Jan}, pages={732–738} }
 @misc{linthicum_gehrke_thomson_carlson_rajagopal_davis_2002, title={Pendeoepitaxial gallium nitride semiconductor layers on silicon carbide substrates}, volume={6,462,355}, number={2002 Oct. 8}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Thomson, D. B. and Carlson, E. P. and Rajagopal, P. and Davis, R. F.}, year={2002} }
 @misc{linthicum_gehrke_thomson_carlson_rajagopal_davis_2002, title={Pendeoepitaxial methods of fabricating gallium nitride semiconductor layers on silicon carbide substrates by lateral growth from sidewalls of masked posts, ang gallium nitratde semiconductor structures fabricated thereby}, volume={6,376,339}, number={2002 Apr. 23}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Thomson, D. B. and Carlson, E. P. and Rajagopal, P. and Davis, R. F.}, year={2002} }
 @misc{linthicum_gehrke_davis_2002, title={Pendeoepitaxial methods of fabricating gallium nitride semiconductor layers on weak posts, and gallium nitride semiconductor structures fabricated thereby}, volume={6,380,108}, number={2002 Apr. 30}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Davis, R. F.}, year={2002} }
 @article{bergman_chen_mcilroy_davis_2002, title={Probing the AlxGa1-xN spatial alloy fluctuation via UV-photoluminescence and Raman at submicron scale}, volume={81}, ISSN={["1077-3118"]}, DOI={10.1063/1.1526918}, abstractNote={We present a straightforward method for the study of alloy spatial compositional distribution at the submicron scale via photoluminescence and Raman spectroscopy. The spatial dependence of the band gap light-emission energy of AlxGa1−xN alloys at composition 0⩽x⩽1 was studied via deep UV-photoluminescence and Raman microscopy in order to address the issue of the spatial alloy fluctuation. The data were acquired in a random fashion from an area of ∼1 mm2 on the sample at steps of ∼1–200 μm utilizing the 244 nm laser line of probing spot size ∼300 nm radius. Our study indicates that the photoluminescence emission energy exhibits random type variations depending on locality: the alloys of composition x=0.12, x=0.22, x=50, and x=0.70 exhibit average variations of ∼10, 30, 45, and 25 meV, respectively. The photoluminescence of the pure GaN exhibits no significant spatial fluctuation. The stress contribution to the observed photoluminescence fluctuations was investigated via Raman analysis and was taken into account in order to estimate the local compositional fluctuation Δx. Our results indicate that for the higher Al composition alloys x=0.50 and 0.70 the stress and the compositional fluctuation can be resolved, resulting in average spatial fluctuations of Δx=0.004 and 0.002, respectively.}, number={22}, journal={APPLIED PHYSICS LETTERS}, author={Bergman, L and Chen, XB and McIlroy, D and Davis, RF}, year={2002}, month={Nov}, pages={4186–4188} }
 @article{roskowski_preble_einfeldt_miraglia_schuck_grober_davis_2002, title={Reduction in dislocation density and strain in GaN thin films grown via maskless pendeo-epitaxy}, volume={10}, number={4}, journal={Opto-electronics Review}, author={Roskowski, A. M. and Preble, E. A. and Einfeldt, S. and Miraglia, P. M. and Schuck, J. and Grober, R. and Davis, R. F.}, year={2002}, pages={261–270} }
 @article{einfeldt_roskowski_preble_davis_2002, title={Strain and crystallographic tilt in uncoalesced GaN layers grown by maskless pendeoepitaxy}, volume={80}, ISSN={["0003-6951"]}, DOI={10.1063/1.1448145}, abstractNote={The strain in thin GaN layers grown by maskless pendeoepitaxy has been investigated using high-resolution x-ray diffraction and finite-element simulations. The crystallographic tilt of the free-hanging wings was determined to result from the strain relaxation of the seed stripes along [0001]. The impact of the dimensions of the pendeostructure and of the formation of crystal defects on the expected wing tilt is discussed.}, number={6}, journal={APPLIED PHYSICS LETTERS}, author={Einfeldt, S and Roskowski, AM and Preble, EA and Davis, RF}, year={2002}, month={Feb}, pages={953–955} }
 @article{einfeldt_diesselberg_heinke_hommel_rudloff_christen_davis_2002, title={Strain in cracked AlGaN layers}, volume={92}, ISSN={["0021-8979"]}, DOI={10.1063/1.1481969}, abstractNote={The strain relaxation due to cracks of different depths in AlGaN layers grown on GaN template layers has been investigated using spatially resolved cathodoluminescence spectroscopy, high-resolution x-ray diffraction and two-dimensional finite element simulations. The experimental data consistently show that the relief of tensile stress increases with decreasing crack spacing. The measured strain profiles between the cracks are well described by the theoretical calculations for small crack spacings; whereas, deviations for larger crack spacings have been found. The latter is discussed in terms of inelastic strain relaxation mechanisms, the reliability of the deformation potential for AlGaN employed in this article, and the spatial variations in the properties of the AlGaN, e.g., its composition.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Einfeldt, S and Diesselberg, M and Heinke, H and Hommel, D and Rudloff, D and Christen, J and Davis, RF}, year={2002}, month={Jul}, pages={118–123} }
 @article{roskowski_miraglia_preble_einfeldt_davis_2002, title={Surface instability and associated roughness during conventional and pendeo-epitaxial growth of GaN(0001) films via MOVPE}, volume={241}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(02)00943-0}, abstractNote={Investigations of the origins of surface roughening in GaN(0 0 0 1) have resulted in the development of a growth process route having an optimum temperature of 1020°C and a film thickness beyond 2.5 μm which results in films with the smoothest surface morphology. Atomic force microscopy (AFM) revealed uncoalesced GaN islands and hillocks for non-optimum temperatures below and above 1020°C, respectively. Uncoalesced islands were a result of insufficient lateral growth. Hillocks were a result of the rotation of heterogeneous steps formed at pure screw or mixed dislocations which terminated on the (0 0 0 1) surface. Growth of the latter features was controlled kinetically by temperature through adatom diffusion. The 106 cm−2 density of hillocks was reduced through growth on thick GaN templates and regions of pendeo-epitaxy (PE) overgrowth with lower pure screw or mixed dislocations. Smooth PE surfaces were obtained at temperatures that reduced the lateral to vertical growth rate but also retarded hillock growth that originated in the stripe regions. The (112̄0) PE sidewall surface was atomically smooth, with a root mean square roughness value of 0.17 nm, which was the noise limited resolution of the AFM measurements.}, number={1-2}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Roskowski, AM and Miraglia, PQ and Preble, EA and Einfeldt, S and Davis, RF}, year={2002}, month={May}, pages={141–150} }
 @article{danielsson_zetterling_ostling_linthicum_thomson_nam_davis_2002, title={The influence of band offsets on the IV characteristics for GaN/SiC heterojunctions}, volume={46}, ISSN={["1879-2405"]}, DOI={10.1016/S0038-1101(01)00346-X}, abstractNote={GaN/SiC heterojunctions can improve the performance considerably for bipolar transistors based on SiC technology. In order to fabricate such devices with a high current gain, the origin of the low turn-on voltage for the heterojunction has to be investigated, which is believed to decrease the minority carrier injection considerably. In this work heterojunction diodes are compared and characterized. For the investigated diodes, the GaN layers have been grown by molecular beam epitaxy (MBE), metal organic chemical vapor deposition, and hydride vapor phase epitaxy. A diode structure fabricated with MBE is presented here, whereas others are collected from previous publications. The layers were grown either with a low temperature buffer, AlN buffer, or without buffer layer. The extracted band offsets are compared and included in a model for a recombination process assisted by tunneling, which is proposed as explanation for the low turn-on voltage. This model was implemented in a device simulator and compared to the measured structures, with good agreement for the diodes with a GaN layer grown without buffer layer. In addition the band offset has been calculated from Schottky barrier measurements, resulting in a type II band alignment with a conduction band offset in the range 0.6–0.9 eV. This range agrees well with the values extracted from capacitance–voltage measurements.}, number={6}, journal={SOLID-STATE ELECTRONICS}, author={Danielsson, E and Zetterling, CM and Ostling, M and Linthicum, K and Thomson, DB and Nam, OH and Davis, RF}, year={2002}, month={Jun}, pages={827–835} }
 @article{platow_oh_nemanich_sayers_hartman_davis_2002, title={TiC nanoisland formation on 6H-SiC(0001)(Si)}, volume={91}, ISSN={["0021-8979"]}, DOI={10.1063/1.1465121}, abstractNote={Spontaneous formation of titanium carbide nanoislands on silicon carbide substrates has been studied with scanning tunneling microscopy and x-ray absorption near-edge spectroscopy. Scratch-free and atomically flat 6H–SiC(0001)Si substrates were prepared by high temperature hydrogen etching. The surfaces were subsequently cleaned by in situ ultrahigh vacuum annealing. Titanium carbide nanoislands were formed by titanium deposition and annealing at 950 °C. The average width (10–50 nm) and separation of the Ti islands was controlled by varying the titanium coverage (0.1–0.3 nm) and the annealing time (1–20 min). At the lowest coverage, the islands were uniformly distributed over the surface, while at higher coverage the islands tended to collect at the substrate step edges.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Platow, W and Oh, J and Nemanich, RJ and Sayers, DE and Hartman, JD and Davis, RF}, year={2002}, month={May}, pages={6081–6084} }
 @article{davis_gehrke_linthicum_preble_rajagopal_ronning_zorman_mehregany_2001, title={Conventional and pendeo-epitaxial growth of GaN(0001) thin films on Si(111) substrates}, volume={231}, ISSN={["1873-5002"]}, DOI={10.1016/S0022-0248(01)01462-2}, abstractNote={Single-crystal wurtzitic GaN(0 0 0 1) films have been grown via conventional methods on high-temperature AlN(0 0 0 1) buffer layers previously deposited on 3C-SiC(1 1 1)/Si(1 1 1) substrates using metal organic vapor phase epitaxy (MOVPE). Formation of the 3C-SiC transition layer employed a carburization step and the subsequent deposition of epitaxial 3C-SiC(1 1 1) on the Si(1 1 1) surface using atmospheric pressure chemical vapor deposition (APCVD) for both processes. Similar films, except with significantly reduced dislocation densities, have been grown via pendeo-epitaxy (PE) from the (112̄0) sidewalls of silicon nitride masked, raised, rectangular, and [11̄00] oriented GaN stripes etched from films conventionally grown on similarly prepared, Si-based, multilayer substrates. The FWHM of the (0 0 0 2) X-ray diffraction peak of the conventionally grown GaN was 1443 arcsec. The FWHM of the photoluminescence (PL) spectra for the near band-edge emission on these films was 19 meV. Tilting in the coalesced PE-grown GaN epilayers of 0.2° was confined to the areas of lateral overgrowth over the masks; no tilting was observed in the material suspended above the trenches. The strong, low-temperature PL band-edge peak at 3.456 eV with an FWHM of 17 meV in the PE films was comparable to that observed in PE GaN films grown on AlN/6H-SiC(0 0 0 1) substrates.}, number={3}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Davis, RF and Gehrke, T and Linthicum, KJ and Preble, E and Rajagopal, P and Ronning, C and Zorman, C and Mehregany, M}, year={2001}, month={Oct}, pages={335–341} }
 @article{platow_nemanich_sayers_hartman_davis_2001, title={Growth of epitaxial CoSi2 on 6H-SiC(0001)(Si)}, volume={90}, ISSN={["1089-7550"]}, DOI={10.1063/1.1412842}, abstractNote={Epitaxial growth of (111)-oriented CoSi2 has been achieved on a scratch-free 6H-SiC(0001)Si substrate. The surface was prepared using atmospheric hydrogen etching and ultrahigh vacuum Si cleaning. A high-quality CoSi2 thin film was obtained by a modified template method and co-deposition of Co and Si at 550 °C. The structure and morphology of the film is studied by means of reflection high electron energy diffraction, x-ray absorption fine structure, x-ray diffraction, and atomic force microscopy.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Platow, W and Nemanich, RJ and Sayers, DE and Hartman, JD and Davis, RF}, year={2001}, month={Dec}, pages={5924–5927} }
 @article{mcginnis_thomson_davis_chen_michel_lamb_2001, title={In situ cleaning of GaN/6H-SiC substrates in NH3}, volume={222}, ISSN={["0022-0248"]}, DOI={10.1016/s0022-0248(00)00947-7}, abstractNote={Metalorganic chemical vapor deposition-grown GaN on 6H-SiC substrates were cleaned by annealing in an NH3 flux. Oxygen contamination was removed by thermal desorption, and carbon removal was facilitated by reaction with NH3. The GaN(0 0 0 1) surface after NH3 beam cleaning at 730°C was smooth with distinct atomic steps. The roughness (0.20 nm RMS) was only slightly greater than that of the untreated substrate (0.17 nm RMS). Carbon and oxygen concentrations were reduced to background levels (∼1 at%) by annealing in an NH3 flux at 800°C. The surface step structure was destroyed by annealing in an NH3 flux of 4×1015 cm−2 s−1 from a seeded supersonic beam; however, annealing in an NH3 flux of 7×1015 cm−2 s−1 from a leak valve inhibited surface roughening and produced a relatively smooth surface (0.28 nm RMS) with a 3×3 R30° reconstruction. We infer from the effects of annealing temperature and NH3 flux that the observed surface roughening is due to GaN decomposition.}, number={3}, journal={JOURNAL OF CRYSTAL GROWTH}, author={McGinnis, AJ and Thomson, D and Davis, RF and Chen, E and Michel, A and Lamb, HH}, year={2001}, month={Jan}, pages={452–458} }
 @misc{ronning_carlson_davis_2001, title={Ion implantation into gallium nitride}, volume={351}, ISSN={["1873-6270"]}, DOI={10.1016/S0370-1573(00)00142-3}, abstractNote={This comprehensive review is concerned with studies regarding ion implanted gallium nitride (GaN) and focuses on the improvements made in recent years. It is divided into three sections: (i) structural properties, (ii) optical properties and (iii) electrical properties. The first section includes X-ray diffraction (XRD), transmission electron microscopy (TEM), secondary ion mass spectroscopy (SIMS), Rutherford Backscattering (RBS), emission channeling (EC) and perturbed γγ-angular correlation (PAC) measurements on GaN implanted with different ions and doses at different temperatures as a function of annealing temperature. The structural changes upon implantation and the respective recovery upon annealing will be discussed. Several standard and new annealing procedures will be presented and discussed. The second section describes mainly photoluminescence (PL) studies, however, the results will be discussed with respect to Raman and ellipsometry studies performed by other groups. We will show that the PL-signal is very sensitive to the processes occurring during implantation and annealing. The results of Hall and C–V measurements on implanted GaN are presented in Section 3. We show and discuss the difficulties in achieving electrical activation. However, optical and electrical properties are both a result of the structural changes upon implantation and annealing. Each section will be critically discussed with respect to the existing literature, and the main conclusions are drawn from the interplay of the results obtained from the different techniques used/reviewed.}, number={5}, journal={PHYSICS REPORTS-REVIEW SECTION OF PHYSICS LETTERS}, author={Ronning, C and Carlson, EP and Davis, RF}, year={2001}, month={Sep}, pages={349–385} }
 @article{mcginnis_thomson_davis_chen_michel_lamb_2001, title={Kinetics and gas-surface dynamics of GaN homoepitaxial growth using NH3-seeded supersonic molecular beams}, volume={494}, ISSN={["1879-2758"]}, DOI={10.1016/S0039-6028(01)01466-2}, abstractNote={The kinetics of homoepitaxial growth of GaN thin films on metal-organic chemical vapor deposition (MOCVD)-grown GaN(0 0 0 1)/AlN/6H-SiC substrates was probed using NH3-seeded supersonic molecular beams. NH3 was seeded in H2 and He and antiseeded in N2 and Ar in order to obtain incident kinetic energies of 0.08–1.8 eV. Nozzle temperatures of 35–600 °C were used to adjust the NH3 internal energy. Intense NH3 beams (fluxes >2×1015cm−2s−1 at the substrate) are produced for low seeding percentages (<5%) in the lighter carrier gases, because the heavier species (NH3) is focused along the centerline of the beam. The NH3 flux is proportional to the ratio of its molecular weight to the average molecular weight of the binary gas mixture. A steady-state Langmuir–Hinshelwood kinetics model was used to extract zero-coverage NH3 sticking coefficient (αNH30) values from GaN growth kinetics data. An αNH30 value of 0.14 at 750 °C was determined using seeded supersonic beams of NH3 in He with incident kinetic energies of 0.4–0.5 eV. In comparison, GaN growth rates using low-energy NH3 molecules (0.03 eV) from a leak valve indicate an αNH30 of 0.29. Growth rate measurements using NH3 beams with kinetic energies of 0.08–1.8 eV confirmed that αNH30 generally decreases with increasing incident kinetic energy, leading us to conclude that NH3 chemisorption on GaN(0 0 0 1) is unactivated and occurs via a precursor-mediated mechanism. Internal energy enhancement of NH3 chemisorption via a precursor-mediated channel is proposed to explain the effects of nozzle temperature on GaN growth kinetics. The effects of NH3 incident kinetic energy on film morphology are indirect. Rough, highly faceted films are observed under Ga-limited growth conditions. The surface morphology of films grown under NH3-limited conditions changes from rough to smooth as the effective V/III ratio is decreased.}, number={1}, journal={SURFACE SCIENCE}, author={McGinnis, AJ and Thomson, D and Davis, RF and Chen, E and Michel, A and Lamb, HH}, year={2001}, month={Nov}, pages={28–42} }
 @article{zheleva_nam_ashmawi_griffin_davis_2001, title={Lateral epitaxy and dislocation density reduction in selectively grown GaN structures}, volume={222}, ISSN={["1873-5002"]}, DOI={10.1016/S0022-0248(00)00832-0}, abstractNote={The results of a comparative study of the defect microstructures at different regions in epitaxial, monocrystalline GaN structures grown selectively within windows in and laterally over SiO2 masks deposited on GaN/AlN/6H–SiC heterostructures are presented. The defects in the GaN grown within the SiO2 windows were predominantly threading dislocations of mostly mixed character with Burgers vector b=1/3〈112̄3〉 and edge dislocations with b=1/3〈112̄0〉 with a density range of 109–1010 cm−2, as determined using transmission electron microscopy (TEM). The regions of lateral epitaxial overgrowth (LEO-GaN) contained short dislocation segments parallel to the interfacial planes, which were usually aligned parallel or nearly parallel to the 〈11̄00〉 or 〈112̄0〉 directions and with densities of ⩽106 cm−2. Specific morphologies exhibited by the LEO-GaN were determined to be associated with the mechanism of stress relaxation. Finite element analysis of these complex heterostructures showed that the accommodation of the mismatches in the coefficients of thermal expansion among the different phases in the heterostructures was manifest in the formation of the curved surfaces observed in cross-sectional TEM.}, number={4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Zheleva, TS and Nam, OH and Ashmawi, WM and Griffin, JD and Davis, RF}, year={2001}, month={Feb}, pages={706–718} }
 @misc{linthicum_gehrke_davis_thomson_tracy_2001, title={Methods of fabricating gallium nitride microelectronic layers on silicon layers and gallium nitride microelectronic structures formed thereby}, volume={6,255,198}, number={2001 July 3}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Davis, R. F. and Thomson, D. B. and Tracy, K. M.}, year={2001} }
 @misc{zheleva_thomson_smith_linthicum_gehrke_davis_2001, title={Methods of fabricating gallium nitride semiconductor layers by lateral growth from sidewalls into trenches, and gallium nitride semiconductor structures fabricated thereby}, volume={6,265,289}, number={2001 July 24}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Zheleva, T. and Thomson, D. B. and Smith, S. A. and Linthicum, K. J. and Gehrke, T. and Davis, R. F.}, year={2001} }
 @misc{gehrke_linthicum_davis_2001, title={Methods of forming a plurality of semiconductor layers using spaced trench arrays}, volume={6,261,929}, number={2001 July 17}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Gehrke, T. and Linthicum, K. J. and Davis, R. F.}, year={2001} }
 @article{chang_oberhofer_muth_kolbas_davis_2001, title={Optical metastability of subband gap (2.2 eV) yellow luminescence in GaN}, volume={79}, ISSN={["0003-6951"]}, DOI={10.1063/1.1381417}, abstractNote={Optical metastability has been studied in undoped GaN films grown on SiC substrates having a previously deposited AlN buffer layer. Brief exposures to a higher intensity ultraviolet light resulted in temporary changes in the optical properties of the GaN layer. The photoinduced changes created high contrast patterns on samples that could be observed under an optical microscope with lower intensity ultraviolet excitation. The subband gap yellow photoluminescence peak at 2.2 eV increased significantly after the patterns were created. This change slowly returned (hours) to its initial value at room temperature. The retention time decreased to a few seconds at temperatures above 100 °C. The data showed that a 1.34 eV thermal activation energy exists, which suggests that the cause of these metastable properties is related to the subband gap yellow luminescence.}, number={3}, journal={APPLIED PHYSICS LETTERS}, author={Chang, YC and Oberhofer, AE and Muth, JF and Kolbas, RM and Davis, RF}, year={2001}, month={Jul}, pages={281–283} }
 @article{davis_gehrke_linthicum_zheleva_rajagopal_zorman_mehregany_2001, title={Pendeo-epitaxial growth and characterization of thin films of gallium nitride and related materials on SiC(0001) and si(111) substrates}, volume={92}, number={2}, journal={Zeitschrift fur MetallkundeAmerican Journal of Physiology}, author={Davis, R. F. and Gehrke, T. and Linthicum, K. J. and Zheleva, T. S. and Rajagopal, P. and Zorman, C. A. and Mehregany, M.}, year={2001}, pages={163–166} }
 @article{davis_gehrke_linthicum_zheleva_preble_rajagopal_zorman_mehregany_2001, title={Pendeo-epitaxial growth of thin films of gallium nitride and related materials and their characterization}, volume={225}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(01)00836-3}, abstractNote={Monocrystalline GaN and AlxGa1−xN films have been grown via the pendeo-epitaxy (PE)1 technique with and without Si3N4 masks on GaN/AlN/6H-SiC(0 0 0 1) and GaN(0 0 0 1)/AlN(0 0 0 1)/3C-SiC(1 1 1)/Si(1 1 1) substrates using organometallic vapor phase deposition. Scanning and transmission electron microscopies were used to evaluate the external microstructures and the distribution of dislocations, respectively. The dislocation densities in the PE grown films were reduced at least five orders of magnitude relative to the initial GaN seed layers. Tilting to 0.2° in the portion of the coalesced GaN epilayers grown over the silicon nitride masks was observed via X-ray diffraction. Neither tilting nor low angle boundaries were observed within areas of coalescence in the material grown on substrates without the masks. The strong, low-temperature PL band-edge peak at 3.45 eV with a FWHM of 17 meV was comparable to that observed in PE GaN films grown on 6H-SiC(0 0 0 1). The band-edge in the GaN grown on AlN(0 0 0 1)/SiC(1 1 1)Si(1 1 1) substrates was shifted to a lower energy by 10 meV, indicative of a greater tensile stress.}, number={2-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Davis, RF and Gehrke, T and Linthicum, KJ and Zheleva, TS and Preble, EA and Rajagopal, P and Zorman, CA and Mehregany, M}, year={2001}, month={May}, pages={134–140} }
 @misc{linthicum_gehrke_thomson_carlson_rajagopal_davis_2001, title={Pendeoepitaxial gallium nitride semiconductor layers on silicon carbide substrates}, volume={6,177,688}, number={2001 Jan. 23}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Thomson, D. B. and Carlson, E. P. and Rajagopal, P. and Davis, R. F.}, year={2001} }
 @article{teng_aboelfotoh_davis_muth_kolbas_2001, title={Photoluminescence and electrical characteristics of the two-dimensional electron gas in Si delta-doped GaN layers}, volume={78}, ISSN={["1077-3118"]}, DOI={10.1063/1.1353836}, abstractNote={We have studied the electrical and photoluminescence (PL) properties of a Si delta-doped GaN layer grown by metalorganic chemical vapor deposition. The Hall mobility and electron sheet concentration are 726 cm2/V s and 1.9×1012 cm−2, respectively, at 2 K. A PL peak located at 78 meV below the band gap of GaN is observed at 77 K. This PL peak is attributed to the radiative recombination between electrons in the two-dimensional quantum states and photoexcited holes in GaN, which is consistent with simulation results using a one-dimensional Poisson and Schrödinger equation solver. The peak disappears at temperatures higher than 77 K and is not observed in uniformly doped GaN layers.}, number={12}, journal={APPLIED PHYSICS LETTERS}, author={Teng, CW and Aboelfotoh, MO and Davis, RF and Muth, JF and Kolbas, RM}, year={2001}, month={Mar}, pages={1688–1690} }
 @article{jia_yu_keogh_asbeck_miraglia_roskowski_davis_2001, title={Polarization charges and polarization-induced barriers in AlxGa1-xN/GaN and InyGa1-yN/GaN heterostructures}, volume={79}, ISSN={["0003-6951"]}, DOI={10.1063/1.1412594}, abstractNote={Polarization charges are measured and the formation of large electrostatic barriers arising primarily as a consequence of the presence of polarization-induced charge densities is deduced from capacitance–voltage analysis of n-type AlxGa1−xN/GaN and InyGa1−yN/GaN heterostructures. In structures consisting of 5–10 nm AlxGa1−xN or InyGa1−yN surrounded by n-GaN, capacitance–voltage profiling studies combined with elementary electrostatic analysis yield experimental estimates of polarization charge densities, which are compared with values expected based on the combined effects of spontaneous and piezoelectric polarization. These results imply the existence of electrostatic barriers that are due primarily to the large polarization charge densities at each heterojunction interface and the resulting potential difference maintained across the thin AlxGa1−xN or InyGa1−yN layers. The electrostatic barriers formed in these structures are large in comparison to the heterojunction conduction-band offsets, demonstrating the utility of polarization-based engineering of electrostatic barriers in nitride semiconductor heterostructures.}, number={18}, journal={APPLIED PHYSICS LETTERS}, author={Jia, L and Yu, ET and Keogh, D and Asbeck, PM and Miraglia, P and Roskowski, A and Davis, RF}, year={2001}, month={Oct}, pages={2916–2918} }
 @article{davis_gehrke_linthicum_rajagopal_roskowski_zheleva_preble_zorman_mehregany_schwarz_et al._2001, title={Review of pendeo-epitaxial growth and characterization of thin films of GaN and AlGaN alloys on 6H-SiC(0001) and Si(111) substrates}, volume={6}, number={14}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Davis, R. F. and Gehrke, T. and Linthicum, K. J. and Rajagopal, P. and Roskowski, A. M. and Zheleva, T. and Preble, E. A. and Zorman, C. A. and Mehregany, M. and Schwarz, U. and et al.}, year={2001}, pages={1–16} }
 @article{roskowski_miraglia_preble_einfeldt_stiles_davis_schuck_grober_schwarz_2001, title={Strain and dislocation reduction in maskless pendeo-epitaxy GaN thin films}, volume={188}, DOI={10.1002/1521-396x(200112)188:2<729::aid-pssa729>3.0.co;2-w}, abstractNote={Measurement of strain in GaN films grown via pendeo-epitaxy (PE) indicates that the overgrowth, or wing, material is crystallographically relaxed. An increase of ≈0.02% in the c-axis lattice parameter of the wing material was measured via high-resolution X-ray diffraction (HRXRD); additional evidence for this increase was indicated by an upward shift of the E2 Raman line frequency. Atomic force microscopy studies revealed a reduction in the density of mixed-type dislocations in the wing. A reduction in screw-type dislocations in the wings with respect to the stripes is indicated by a reduction in HRXRD rocking curve FWHM of the (0002) reflections from 646 to 354 arcsec. The off-axis FWHM of the wing area was 126 arcsec compared to 296 arcsec for the stripe indicating a reduction in the edge-type dislocations as well. Pendeo-epitaxy growth of wings off the (110) surface of a GaN stripe produced a material that is crystallographically relaxed, contains fewer defects compared to the stripe and is atomically smooth on the (110) surface.}, number={2}, journal={Physica Status Solidi. A, Applications and Materials Science}, author={Roskowski, A. M. and Miraglia, P. Q. and Preble, E. A. and Einfeldt, S. and Stiles, T. and Davis, R. F. and Schuck, J. and Grober, R. and Schwarz, U.}, year={2001}, pages={729–732} }
 @article{pozina_edwards_bergman_monemar_bremser_davis_2001, title={Time-resolved photoluminescence in strained GaN layers}, volume={183}, number={1}, journal={Physica Status Solidi. A, Applications and Materials Science}, author={Pozina, G. and Edwards, N. V. and Bergman, J. P. and Monemar, B. and Bremser, M. D. and Davis, R. F.}, year={2001}, pages={151–155} }
 @article{pozina_edwards_bergman_paskova_monemar_bremser_davis_2001, title={Time-resolved spectroscopy of strained GaN/AlN/6H-SiC heterostructures grown by metalorganic chemical vapor deposition}, volume={78}, ISSN={["0003-6951"]}, DOI={10.1063/1.1350421}, abstractNote={Temperature-dependent time-resolved photoluminescence measurements were performed on GaN film/AlN buffer/6H–SiC substrate heterostructures grown by metalorganic chemical vapor deposition. The overlying GaN layers were under tension, as estimated from the free A exciton (FEA) position. The recombination lifetimes were determined for the FEA and for the neutral-donor-bound exciton (D0X). We observed that the recombination lifetime for the FEA has the same value of 40–50 ps in all the layers, whereas the recombination time for the D0X varies for different samples. We observed that the recombination lifetimes for D0X have a clear dependence on the position of FEA, i.e., the recombination lifetime increases with decreasing strain in the layers. We discuss the results in term of the hole states involved in the donor-bound exciton recombination.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Pozina, G and Edwards, NV and Bergman, JP and Paskova, T and Monemar, B and Bremser, MD and Davis, RF}, year={2001}, month={Feb}, pages={1062–1064} }
 @article{liaw_doyle_fejes_zollner_konkar_linthicum_gehrke_davis_2000, title={Crystallinity and microstructures of aluminum nitride films deposited on Si(111) substrates}, volume={44}, ISSN={["1879-2405"]}, DOI={10.1016/S0038-1101(99)00307-X}, abstractNote={The crystallinity and microstructures of MOCVD AlN films deposited on Si(111) substrates with and without a buffer layer(s) were determined. The buffer layers were a thin 3C–SiC(111) layer produced via conversion of a Si(111) surface and a film stack consisting of graded-AlxGa1−xN/GaN/3C–SiC. A randomly oriented polycrystalline AlN film was obtained when this material was deposited directly on the Si(111). The use of a buffer layer led to the growth and coalescence of highly oriented AlN films produced by the coalescence of grains having average misalignments along the c-axis of 1.8° and that on the c-plane of 3.3°. The grains exhibited strongly faceted tips. The 2H–AlN(0001) films grown on a 3C–SiC(111) buffer layers showed adequate crystal perfection for use as a template for growth of single-crystal GaN and/or AlxGa1−xN films.}, number={4}, journal={SOLID-STATE ELECTRONICS}, author={Liaw, HM and Doyle, R and Fejes, PL and Zollner, S and Konkar, A and Linthicum, KJ and Gehrke, T and Davis, RF}, year={2000}, month={Apr}, pages={747–755} }
 @article{danielsson_zetterling_ostling_lee_linthicum_thomson_nam_davis_2000, title={Dry etching and metallization schemes in a GaN/SiC heterojunction device process}, volume={338}, number={3}, journal={Materials Science Forum}, author={Danielsson, E. and Zetterling, C. M. and Ostling, M. and Lee, S. K. and Linthicum, K. J. and Thomson, D. B. and Nam, O. H. and Davis, R. F.}, year={2000}, pages={1049–1052} }
 @misc{davis_nam_zheleva_bremser_2000, title={Gallium nitride semiconductor structures including a lateral gallium nitride layer that extends from an underlying gallium nitride layer}, volume={6,051,849}, number={2000 Apr. 18}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Davis, R. F. and Nam, O.-H. and Zheleva, T. and Bremser, M. D.}, year={2000} }
 @article{balkas_sitar_bergman_shmagin_muth_kolbas_nemanich_davis_2000, title={Growth and characterization of GaN single crystals}, volume={208}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(99)00445-5}, abstractNote={Up to 3 mm long GaN single crystals were grown by sublimation of cold pressed GaN pellets or evaporation of gallium (Ga) metal under an ammonia (NH3) flow in a dual heater, high-temperature growth system. A growth rate of 500 μm/h along the [0 0 0 1] direction was achieved using a source temperature of 1200°C, a total pressure of 760 Torr, and an NH3 flow rate of 50 sccm. The resulting crystals were transparent, possessed low aspect ratios and well-defined growth facets. The only impurity present at high concentrations was oxygen (3×1018 atoms/cm3). Photoluminescence studies conducted at 77 K showed a sharp emission peak centered at 359 nm. Time-dependent photoluminescence measurements revealed optical metastability in bulk GaN. Raman spectroscopy yielded narrow peaks representing only the modes allowed for the wurtzite structure. All characterization studies confirmed excellent crystalline and optical quality of the obtained single crystals.}, number={1-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Balkas, CM and Sitar, Z and Bergman, L and Shmagin, IK and Muth, JF and Kolbas, R and Nemanich, RJ and Davis, RF}, year={2000}, month={Jan}, pages={100–106} }
 @article{michel_hanser_davis_qiao_lau_yu_sun_asbeck_2000, title={Growth and characterization of piezoelectrically enhanced acceptor-type AlGaN/GaN heterostructures}, volume={5}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Michel, A. and Hanser, D. and Davis, R. F. and Qiao, D. and Lau, S. S. and Yu, L. S. and Sun, W. and Asbeck, P.}, year={2000}, pages={U520–525} }
 @article{hanser_banks_davis_jahnen_albrecht_dorsch_christiansen_strunk_2000, title={Growth and microstructure of InxGa1-xN films grown on SiC substrates via low pressure metalorganic vapor phase epitaxy}, volume={3}, ISSN={["1873-4081"]}, DOI={10.1016/S1369-8001(99)00023-2}, abstractNote={Abstract The growth and microstructures of InxGa1−xN films (x≤0.23) grown on α(6H)–SiC(0001) wafer/AIN buffer layer/GaN heterostructures by low pressure metalorganic vapor phase epitaxy have been investigated. The system deposition pressure limited the InN content in these films. The maximum InN contents achievable at the deposition pressures of 45 and 90 torr were ∼13 and ∼23%, respectively. Kinetic phenomena based on the rates of adsorption and desorption of the In growth species off the growth surface are presented to explain the film composition dependence on the system pressure. The surface morphologies and microstructures of the InxGa1−xN films were analyzed using several techniques, and the formation of pinhole defects in the films was investigated. Most of the pinhole defects were associated with threading dislocations with a c-component Burgers vector. Edge-type dislocations were never observed to terminate in pinholes in the samples observed here. Indium segregation to areas around the defect areas was observed, as was an In compositional gradient in the growth direction. Based on experimental observations, the strain field around dislocations with a c-component Burgers vector could result in the increase of In atoms at the dislocation sites in the film, which result in a change to the local growth mode of the film and causes the pinhole defects to form.}, number={3}, journal={MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING}, author={Hanser, AD and Banks, AD and Davis, RF and Jahnen, B and Albrecht, M and Dorsch, W and Christiansen, S and Strunk, HP}, year={2000}, month={Jun}, pages={163–171} }
 @article{collazo_schlesser_roskowski_davis_sitar_2000, title={Hot electron transport in AlN}, volume={88}, ISSN={["0021-8979"]}, DOI={10.1063/1.1318386}, abstractNote={The energy distribution of electrons that were transported through a thin intrinsic AlN film was directly measured as a function of the applied field. The measurements were realized by extracting the electrons into vacuum through a semitransparent Au contact and measuring their energies using an electron spectrometer. At moderate applied fields (100 kV/cm), the energy distribution was found to follow a Maxwellian model corresponding to a temperature of 2700 K and a drift component below the spectrometer resolution. At higher fields, intervalley scattering was evidenced by the presence of a second peak at 0.7 eV. This coincides well with the energy position of the LM valleys in AlN.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Collazo, R and Schlesser, R and Roskowski, A and Davis, RF and Sitar, Z}, year={2000}, month={Nov}, pages={5865–5869} }
 @article{suvkhanov_parikh_usov_hunn_withrow_thomson_gehrke_davis_krasnobaev_2000, title={Influence of annealing conditions on dopant activation of Si+ and Mg+ implanted GaN}, volume={338}, number={3}, journal={Materials Science Forum}, author={Suvkhanov, A. and Parikh, N. and Usov, I. and Hunn, J. and Withrow, S. and Thomson, D. and Gehrke, T. and Davis, R. F. and Krasnobaev, L. Y.}, year={2000}, pages={1615–1618} }
 @article{ronning_dalmer_uhrmacher_restle_vetter_ziegeler_hofsass_gehrke_jarrendahl_davis_2000, title={Ion implanted dopants in GaN and AlN: Lattice sites, annealing behavior, and defect recovery}, volume={87}, ISSN={["1089-7550"]}, DOI={10.1063/1.372154}, abstractNote={The recovery of structural defects in gallium nitride (GaN) and aluminum nitride (AlN) after implantation of In+111 and Sr+89 in the dose range (0.1–3) 1013 cm−2 and ion energies of 60–400 keV has been investigated as a function of annealing temperature with emission channeling (EC) and perturbed γγ angular correlation spectroscopy. The implanted In and Sr atoms occupied substitutional sites in heavily perturbed surroundings of point defects after room temperature implantation. No amorphization of the lattice structure was observed. The point defects could be partly removed after annealing to 1473 K for 10–30 min. Lattice site occupation of implanted light alkalis, Na+24 in GaN and AlN as well as Li+8 in AlN, were also determined by EC as a function of implantation and annealing temperature. These atoms occupied mainly interstitial sites at room temperature. Lithium diffusion and the occupation of substitutional sites was observed in GaN and AlN at implantation temperatures above 700 K. A lattice site change was also observed for sodium in AlN, but not in GaN after annealing to 1073 K for 10 min.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Ronning, C and Dalmer, M and Uhrmacher, M and Restle, M and Vetter, U and Ziegeler, L and Hofsass, H and Gehrke, T and Jarrendahl, K and Davis, RF}, year={2000}, month={Mar}, pages={2149–2157} }
 @article{davis_nam_zheleva_gehrke_linthicum_rajagopal_2000, title={Lateral- and pendeo-epitaxial growth and defect reduction in GaN thin films}, volume={338}, number={3}, journal={Materials Science Forum}, author={Davis, R. F. and Nam, O. H. and Zheleva, T. S. and Gehrke, T. and Linthicum, K. J. and Rajagopal, P.}, year={2000}, pages={1471–1476} }
 @article{edwards_bremser_batchelor_buyanova_madsen_yoo_welhkamp_wilmers_cobet_esser_et al._2000, title={Optical characterization of wide bandgap semiconductors}, volume={364}, ISSN={["0040-6090"]}, DOI={10.1016/S0040-6090(99)00903-7}, abstractNote={Our work primarily concerns the characterization of wide-gap III-V nitride semiconductors, nondestructively and at variable temperature, with spectroscopic ellipsometry (SE) and reflectometry in the spectral range from 1.5 to 6 eV. In the case of GaN, there are three main concerns associated with such data: (a) the quantification of the dispersion of the index of refraction with energy, (b) the removal of surface overlayers in real-time, and (c) the determination of the variation of valence bands with biaxial stress and the quantification of residual stress in thin films. The SE and reflectance capabilities provide (1) broadband spectra from 1.5 to 6 eV, which yield information about (a) below the bandgap and (b) above it, and (2) high resolution spectra (less than 1 meV at 3.4 eV) in the vicinity of the gap (3.3-3.6 eV), which enables (c). Here we will discuss issues concerning the relation of (c) to GaN material and growth parameters, though similar data for other wide bandgap materials will be discussed where relevant. Specifically, optimal heterostructure design for potential valence band engineering applications will be discussed in the context of trends in residual stress as a function of film thickness, growth temperature and substrate orientation for GaN/AlN/6H-SiC heterostructures. Standard heterostructures are mostly compressive for samples less than about 0.7 µm thick, are tensile up to about 2 µm and then abruptly become less tensile with stress values near 1 kbar thereafter. Additionally, these trends can be circumvented for moderately thick (approximately 2 µm) GaN layers (normally>2 kbar, tensile) by the introduction of a `buried interface' approach, namely, a strain mediating layer (SML) above the standard high-temperature AlN buffer layer designed to yield a range of compressive stresses from 0 to 2 kbar. The strain characteristics but also the growth rates of subsequently deposited nitride layers can be modulated by changing the growth parameters of the SML. This is achieved by in situ techniques during crystal growth without degrading the optical and structural properties of the deposited layer, as confirmed by XRD, SEM, PL, and AFM data taken on the overlying GaN layers. These results are interpreted in terms of coefficient of thermal expansion data for the layers and data concerning the planarization of GaN layers and growth behavior in non-(0001) directions.}, number={1-2}, journal={THIN SOLID FILMS}, author={Edwards, NV and Bremser, MD and Batchelor, AD and Buyanova, IA and Madsen, LD and Yoo, SD and Welhkamp, T and Wilmers, K and Cobet, C and Esser, N and et al.}, year={2000}, month={Mar}, pages={98–106} }
 @article{davis_gehrke_linthicum_zheleva_rajagopal_zorman_mehregany_2000, title={Pendeo-epitaxial growth and characterization of GaN and related materials on (6H-SiC(0001) and Si(111) substrates}, volume={5}, number={2000}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Davis, R. F. and Gehrke, T. and Linthicum, K. J. and Zheleva, T. S. and Rajagopal, P. and Zorman, C. A. and Mehregany, M.}, year={2000}, pages={U46–57} }
 @article{gehrke_linthicum_preble_rajagopal_ronning_zorman_mehregany_davis_2000, title={Pendeo-epitaxial growth of gallium nitride on silicon substrates}, volume={29}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-000-0068-6}, number={3}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Gehrke, T and Linthicum, KJ and Preble, E and Rajagopal, P and Ronning, C and Zorman, C and Mehregany, M and Davis, RF}, year={2000}, month={Mar}, pages={306–310} }
 @article{gehrke_linthicum_rajagopal_preble_carlson_robin_davis_2000, title={Pendeo-epitaxy (TM) process for aluminum gallium nitride thin films on silicon carbide substrates via metalorganic chemical vapor deposition}, volume={338}, number={3}, journal={Materials Science Forum}, author={Gehrke, T. and Linthicum, K. J. and Rajagopal, P. and Preble, E. A. and Carlson, E. P. and Robin, B. M. and Davis, R. F.}, year={2000}, pages={1491–1494} }
 @article{hartman_naniwae_petrich_ramachandran_feenstra_nemanich_davis_2000, title={Photo-emission electron microscopy (PEEM) of cleaned and etched 6H-SiC(0001)}, volume={338-3}, ISBN={["*************"]}, ISSN={["0255-5476"]}, DOI={10.4028/www.scientific.net/msf.338-342.353}, journal={SILICON CARBIDE AND RELATED MATERIALS - 1999 PTS, 1 & 2}, author={Hartman, JD and Naniwae, K and Petrich, C and Ramachandran, V and Feenstra, RM and Nemanich, RJ and Davis, RF}, year={2000}, pages={353–356} }
 @article{ronning_hofsass_stotzler_deicher_carlson_hartlieb_gehrke_rajagopal_davis_2000, title={Photoluminescence characterization of Mg implanted GaN}, volume={5}, number={2000}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Ronning, C. and Hofsass, H. and Stotzler, A. and Deicher, M. and Carlson, E. P. and Hartlieb, P. J. and Gehrke, T. and Rajagopal, P. and Davis, R. F.}, year={2000}, pages={U622–628} }
 @article{ward_hartman_hurt_tracy_davis_nemanich_2000, title={Schottky barrier height and electron affinity of titanium on AIN}, volume={18}, ISSN={["1071-1023"]}, DOI={10.1116/1.1303733}, abstractNote={Approximately 100 or 1000 Å of AlN was deposited on the (0001)Si-face of on-axis n-type 6H–SiC. The surfaces were examined by ultraviolet photoemission spectroscopy (UPS) utilizing the He I α (21.2 eV) and the He II α (40.8 eV) excitation. Experimental difficulties are discussed. Titanium was deposited on the clean surface of in situ grown AlN. The titanium–AlN interface was also characterized with UPS. Two approaches are presented to identify the valence band maximum (VBM) and the electron affinity χ of the clean surface of AlN was found to be either 0 to 1 eV depending upon the position of the valence band edge. The same assumptions were applied to the analysis of the Ti/AlN interface and, for the case of χ=0 eV, the position of the valence band maximum is 3.4 eV below the position of the Fermi level. For the case of χ=1 eV, the position of the valence band maximum is 4.4 eV below the position of the Fermi level. Therefore, the p-type Schottky barrier height of titanium on AlN is measured to be 3.4±0.2 or 4.4±0.2 eV for χ=0 eV and χ=1 eV, respectively. Independent of the selection of the valence band maximum, the observed Schottky barrier differed from that predicted by the Schottky–Mott model by 1.5±0.2 eV.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Ward, BL and Hartman, JD and Hurt, EH and Tracy, KM and Davis, RF and Nemanich, RJ}, year={2000}, pages={2082–2087} }
 @article{smith_lampert_rajagopal_banks_thomson_davis_2000, title={Selective etching of GaN over AlN using an inductively coupled plasma and an O-2/Cl-2/Ar chemistry}, volume={18}, ISSN={["1520-8559"]}, DOI={10.1116/1.582270}, abstractNote={An alternative method for achieving etching selectivity between GaN and AlN has been demonstrated. The etch rate of AlN was significantly decreased by the addition of a low concentration of O2 to a Cl2–Ar mixture in an inductively coupled plasma (ICP) etching system. The etch rate of GaN in the O2-containing plasma was approximately 15% less than the plasma without the O2 for the same parameters. The pressure and the ICP power were varied to achieve a maximum selectivity of 48 at a pressure of 10 mTorr, a direct current bias of −150 V, and an ICP power of 500 W. The etch rates of GaN and AlN at these parameters were 4800 and 100 Å/min, respectively.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Smith, SA and Lampert, WV and Rajagopal, P and Banks, AD and Thomson, D and Davis, RF}, year={2000}, pages={879–881} }
 @article{zetterling_ostling_yano_kimoto_matsunami_linthicum_davis_2000, title={SiC MISFETs with MBE-grown AlN gate dielectric}, volume={338}, number={3}, journal={Materials Science Forum}, author={Zetterling, C. M. and Ostling, M. and Yano, H. and Kimoto, T. and Matsunami, H. and Linthicum, K. and Davis, R. F.}, year={2000}, pages={1315–1318} }
 @article{kaminska_piotrowska_barcz_jasinski_zielinski_golaszewska_davis_goldys_tomsia_2000, title={Zirconium mediated hydrogen outdiffusion from p-GaN}, volume={5}, number={2000}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Kaminska, E. and Piotrowska, A. and Barcz, A. and Jasinski, J. and Zielinski, M. and Golaszewska, K. and Davis, R. F. and Goldys, E. and Tomsia, K.}, year={2000}, pages={U491–496} }
 @article{gruss_davis_1999, title={Adhesion measurement of zirconium nitride and amorphous silicon carbide coatings to nickel and titanium alloys}, volume={114}, ISSN={["0257-8972"]}, DOI={10.1016/S0257-8972(99)00042-0}, abstractNote={Polycrystalline ZrN and amorphous Si0.57C0.43 coatings were deposited by cathodic arc evaporation and by plasma-assisted chemical vapor deposition (PACVD) respectively on Incoloy 825 (Inc. 825), Hastelloy C22 (Hast. C22) and Titanium Grade 12 (Ti. 12) substrates. Scratch tests were employed to assess the critical load for interfacial failure and fracture mechanisms for the various coating systems. Critical loads, characterized by continuous delamination of the coating, occurred at 41.2 N, 44.1 N and 29.4 N for ZrN deposited on Hast. C22, Inc. 825 and Ti. 12 respectively. Interfacial failure of the Si0.57C0.43-coated metallic substrates was dominated by brittle fracture of the Si0.57C0.43 coating. Critical loads of 2.9 N, 3.9 N and 6.8 N were obtained for Si0.57C0.43 deposited on Inc. 825, Hast. C22 and Ti. 12 respectively. Work of adhesion values were calculated from two well-known models, namely the Bull–Rickerby and Laugier models, and from a model that incorporates elastic–plastic indentation. The ranking of the adhesion for the coating–metal substrate combinations is (from best to worst): ZrN–Inc. 825, ZrN–Hast. C22, ZrN–Ti, Si0.57C0.43–Ti, Si0.57C0.43–Hast. C22 and Si0.57C0.43–Inc. 825.}, number={2-3}, journal={SURFACE & COATINGS TECHNOLOGY}, author={Gruss, KA and Davis, RF}, year={1999}, month={May}, pages={156–168} }
 @article{ronning_linthicum_carlson_hartlieb_thomson_gehrke_davis_1999, title={Characterization of Be-implanted GaN annealed at high temperatures}, volume={4S1}, number={G3.17}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Ronning, C. and Linthicum, K. J. and Carlson, E. P. and Hartlieb, P. J. and Thomson, D. B. and Gehrke, T. and Davis, R. F.}, year={1999} }
 @article{therrien_niimi_gehrke_lucovsky_davis_1999, title={Charge redistribution at GaN-Ga2O3 interfaces: A microscopic mechanism for low defect density interfaces in remote plasma processed MOS devices prepared on polar GaN faces}, volume={48}, ISSN={["0167-9317"]}, DOI={10.1016/s0167-9317(99)00394-9}, abstractNote={Abstract Interfacial defect densities are typically two orders of magnitude higher at [III–V]-dielectric interfaces than at SiSiO 2 interfaces. This paper demonstrates GaN devices with significantly reduced interfacial defect densities using a two step remote plasma process to form the GaN-dielectric interface and then deposit the dielectric film. Separate plasma oxidation and deposition steps have previously been used for fabrication of aggressively scaled Si devices. Essentially the same 300°C remote plasma processing has been applied to GaN metal-oxide semiconductor (MOS) capacitors and field effect transistors (FETs). This paper i) discusses the low temperature plasma process for GaN device fabrication, ii) briefly reviews GaN device performance, and then iii) presents a chemical bonding model that provides a basis for the improved interface electrical properties.}, number={1-4}, journal={MICROELECTRONIC ENGINEERING}, author={Therrien, R and Niimi, H and Gehrke, T and Lucovsky, G and Davis, R}, year={1999}, month={Sep}, pages={303–306} }
 @article{therrien_lucovsky_davis_1999, title={Charge redistribution at GaN-Ga2O3 interfaces: A microscopic mechanism for low defect density interfaces in remote plasma processed MOS devices prepared on polar GaN faces}, volume={176}, ISSN={["0031-8965"]}, DOI={10.1002/(sici)1521-396x(199911)176:1<793::aid-pssa793>3.0.co;2-v}, abstractNote={Interfacial defect densities, typically two orders of magnitude lower than those usually obtained at [III–V]-dielectric interfaces, have been demonstrated for GaN capacitors and field effect transistors (FETs). Separate and independently controlled interface formation and film deposition by remote plasma-assisted processing steps performed at 300 °C were employed. The interfacial oxide is Ga2O3, and the deposited gate dielectric is SiO2. Models for the chemical bonding at the GaN–Ga2O3 interface and at the internal dielectric Ga2O3–SiO2 are presented. The most important aspect of the interface formation involves a redistribution of electrons in the surface atom dangling bonds of the GaN polar face that promotes formation of two-electron bonds with the interfacial dielectric.}, number={1}, journal={PHYSICA STATUS SOLIDI A-APPLIED RESEARCH}, author={Therrien, R and Lucovsky, G and Davis, RF}, year={1999}, month={Nov}, pages={793–796} }
 @article{king_kern_benjamin_barnak_nemanich_davis_1999, title={Chemical vapor cleaning of 6H-SiC surfaces}, volume={146}, ISSN={["0013-4651"]}, DOI={10.1149/1.1392494}, abstractNote={The techniques (temperature range of study) of in situ thermal desorption (500-1100°C) and chemical vapor cleaning (CVC) via exposure to SiH 4 and/or C 2 H 4 (750-1100°C) have been investigated for preparing 6H SiC [(0001) Si , (0001) C , (1120), and (1010)] surfaces suitable for epitaxial growth of SiC and III-nitride films, and are compared with regard to surface purity, stoichiometry, and structural order. Oxide removal below the detection limits of Auger electron spectroscopy was achieved for all orientations via annealing in 200 L SiH 4 at 850-900°C or 200° lower than necessary by thermal desorption. No non-SiC carbon was detected on the surface by X-ray photoelectron spectroscopy. An approximately one-tenth of a monolayer of oxygen coverage and significant quantities of non-SiC carbon were detected for all 6H-SiC surfaces prepared by thermal desorption. In contrast to the predominantly non-SiC carbon-rich surfaces prepared by thermal desorption, the stoichiometry of the SiC surfaces prepared by CVC could be manipulated from Si-rich to C-rich without non-SiC carbon formation by either extending the SiH 4 exposures or by following with C 2 H 4 exposure. The latter surfaces also had lower concentrations of both oxygen and non-SiC carbon and increased surface order.}, number={9}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={King, SW and Kern, RS and Benjamin, MC and Barnak, JP and Nemanich, RJ and Davis, RF}, year={1999}, month={Sep}, pages={3448–3454} }
 @article{king_nemanich_davis_1999, title={Dry ex situ cleaning processes for (0001)(Si) 6H-SiC surfaces}, volume={146}, ISSN={["0013-4651"]}, DOI={10.1149/1.1391986}, abstractNote={A completely dry ex situ cleaning process based on UV/O 3 oxidation and HF vapor exposure for removal of residual C and oxide, respectively, from (0001) Si [the silicon-terminated surface of SiC] 6H-SiC surfaces to levels equivalent to or better than conventional wet chemical ex situ processing has been demonstrated. X-ray photoelectron spectroscopy (XPS) of surfaces exposed to UV-generated ozone revealed the formation of carbon and silicon oxides, as indicated by the broad Si-O Si 2p peak at 102.4 eV (full width at half-maximum = 2.1 eV) and a shift in the surface C 1s peak from 283.6 to 284.2 eV, respectively. Evidence for a reduction in the amount of surface C was shown by an increase in the ratio of the SiC C peak to the surface C peak from 0.8 to 2.7 after the UV/O 3 treatment. Removal of the UV/O 3 silicon oxide via exposure to the vapor from a 10:1 buffered HF solution was indicated by the absence (below the XPS detection limit) of the Si-O Si 2p peak at 102.4 eV. However, this last process results in a F-terminated surface.}, number={7}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={King, SW and Nemanich, RJ and Davis, RF}, year={1999}, month={Jul}, pages={2648–2651} }
 @article{roberson_finello_davis_1999, title={Electrochemical evaluation of molybdenum nitride electrodes in H2SO4 electrolyte}, volume={29}, ISSN={["0021-891X"]}, DOI={10.1023/A:1003460529736}, number={1}, journal={JOURNAL OF APPLIED ELECTROCHEMISTRY}, author={Roberson, SL and Finello, D and Davis, RF}, year={1999}, month={Jan}, pages={75–80} }
 @article{buyanova_wagner_chen_edwards_monemar_lindstrom_bremser_davis_amano_akasaki_1999, title={Electronic structure of the 0.88-eV luminescence center in electron-irradiated gallium nitride}, volume={60}, number={3}, journal={Physical Review. B, Condensed Matter and Materials Physics}, author={Buyanova, I. A. and Wagner, M. and Chen, W. M. and Edwards, N. V. and Monemar, B. and Lindstrom, J. L. and Bremser, M. D. and Davis, R. F. and Amano, H. and Akasaki, I.}, year={1999}, pages={1746–1751} }
 @article{skierbiszewski_suski_leszczynski_shin_skowronski_bremser_davis_1999, title={Evidence for localized Si-donor state and its DX-like properties in AlGaN: Errata (vol 74, pg 3833, 1999)}, volume={75}, number={20}, journal={Applied Physics Letters}, author={Skierbiszewski, C. and Suski, T. and Leszczynski, M. and Shin, M. and Skowronski, M. and Bremser, M. D. and Davis, R. F.}, year={1999}, pages={3225A} }
 @article{skierbiszewski_suski_leszczynski_shin_skowronski_bremser_davis_1999, title={Evidence for localized Si-donor state and its metastable properties in AlGaN}, volume={74}, ISSN={["0003-6951"]}, DOI={10.1063/1.124195}, abstractNote={Transport studies of AlxGa1−xN (0.5<x<0.6) doped with Si have been performed in the pressure range up to 1.4 GPa. For these alloys, the Si dopant forms two donor states. One of them has an effective mass character and the other one represents the localized state strongly coupled to the crystal lattice (metastable state). The localized state of Si forms the corresponding level in the gap for x exceeding 0.5. For the higher x, an increase of the activation energy of this state occurs. Metastable properties of the localized state of Si lead to a persistent photoconductivity effect and to a pressure induced freeze-out of electrons.}, number={25}, journal={APPLIED PHYSICS LETTERS}, author={Skierbiszewski, C and Suski, T and Leszczynski, M and Shin, M and Skowronski, M and Bremser, MD and Davis, RF}, year={1999}, month={Jun}, pages={3833–3835} }
 @article{hanser_nam_bremser_thomson_gehrke_zheleva_davis_1999, title={Growth, doping and characterization of epitaxial thin films and patterned structures of AlN, GaN, and AlxGa1-xN}, volume={8}, ISSN={["1879-0062"]}, DOI={10.1016/S0925-9635(98)00341-0}, abstractNote={Advancements in the doping of GaN and AlxGa1−xN thin films, and the growth of GaN and AlxGa1−xN structures on patterned heterostructure substrates via metalorganic vapor phase epitaxy are reported. The acceptor-type behavior of Mg-doped GaN films grown in N2 diluents is presented. Net ionized impurity concentrations up to 8×1018 cm−3 and Hall mobilities up to ≈14 cm2 V−1 s−1 were measured for Mg-doped films grown in N2 in the as-grown condition. Donor and acceptor doping of AlxGa1−xN alloys was performed. Acceptor doping of AlxGa1−xN for x≤0.13 and donor doping for x≤0.58 were achieved for films deposited at 1100 °C. Lateral epitaxial overgrowth of GaN and AlxGa1−xN layers was investigated. The growth and coalescence of GaN and AlxGa1−xN stripes patterned in SiO2 and/or SiNx masks deposited on GaN, including aligned second lateral epitaxial overgrowth on initial laterally overgrown GaN layers, are discussed.}, number={2-5}, journal={DIAMOND AND RELATED MATERIALS}, author={Hanser, AD and Nam, OH and Bremser, MD and Thomson, DB and Gehrke, T and Zheleva, TS and Davis, RF}, year={1999}, month={Mar}, pages={288–294} }
 @misc{roberson_finello_davis_1999, title={High surface area molybdenum nitride electrodes}, volume={5,935,648}, number={1999 Aug. 10}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Roberson, S. L. and Finello, D. and Davis, R. F.}, year={1999} }
 @article{pavlovska_torres_edwards_bauer_smith_doak_tsong_thomson_davis_1999, title={Homoepitaxial GaN layers studied by low-energy electron microscopy, atomic force microscopy and transmission electronmicroscopy}, volume={176}, number={1}, journal={Physica Status Solidi. A, Applications and Materials Science}, author={Pavlovska, A. and Torres, V. M. and Edwards, J. L. and Bauer, E. and Smith, D. J. and Doak, R. B. and Tsong, I. S. T. and Thomson, D. B. and Davis, R. F.}, year={1999}, pages={469–473} }
 @article{nemanich_english_hartman_sowers_ward_ade_davis_1999, title={Imaging electron emission from diamond and III-V nitride surfaces with photo-electron emission microscopy}, volume={146}, ISSN={["0169-4332"]}, DOI={10.1016/S0169-4332(99)00021-5}, abstractNote={Wide bandgap semiconductors such as diamond and the III–V nitrides (GaN, AlN, and AlGaN alloys) exhibit small or even negative electron affinities. Results have shown that different surface treatments will modify the electron affinity of diamond to cause a positive or negative electron affinity (NEA). This study describes the characterization of these surfaces with photo-electron emission microscopy (PEEM). The PEEM technique is unique in that it combines aspects of UV photoemission and field emission. In this study, PEEM images are obtained with either a traditional Hg lamp or with tunable UV excitation from a free electron laser. The UV-free electron laser at Duke University provides tunable emission from 3.5 to greater than 7 eV. PEEM images of boron or nitrogen (N)-doped diamond are similar to SEM of the same surface indicating relatively uniform emission. For the N-doped samples, PEEM images were obtained for different photon energies ranging from 5.0 to 6.0 eV. In these experiments, the hydrogen terminated surface showed more intense PEEM images at lower photon energy indicating a lower photothreshold than annealed surfaces which are presumed to be adsorbate free. For the nitrides, the emission properties of an array of GaN emitter structures is imaged. Emission is observed from the peaks, and relatively uniform emission is observed from the array. The field at the sample surface is approximately 10 V/μm which is sufficient to obtain an image without UV light. This process is termed field emission electron microscopy (FEEM).}, number={1-4}, journal={APPLIED SURFACE SCIENCE}, author={Nemanich, RJ and English, SL and Hartman, JD and Sowers, AT and Ward, BL and Ade, H and Davis, RF}, year={1999}, month={May}, pages={287–294} }
 @article{pavlovska_torres_bauer_doak_tsong_thomson_davis_1999, title={Low-energy electron microscopy observations of GaN homoepitaxy using a supersonic jet source}, volume={75}, ISSN={["0003-6951"]}, DOI={10.1063/1.124575}, abstractNote={A study of the homoepitaxial growth of GaN(0001) layers was conducted in situ and in real time using the low-energy electron microscope. The Ga flux was supplied by an evaporative cell while the NH3 flux was supplied via a seeded-beam supersonic jet source. At growth temperatures of 665 °C and 677 °C, smooth GaN(0001) layers with well-defined step structures were grown on GaN(0001) substrates prepared by metalorganic chemical vapor deposition. In general, nonfaceted homoepitaxial layers were achieved when the Ga/NH3 flux ratios exceeded 2, starting with a Ga-covered substrate surface, in the temperature range of 655–710 °C.}, number={7}, journal={APPLIED PHYSICS LETTERS}, author={Pavlovska, A and Torres, VM and Bauer, E and Doak, RB and Tsong, IST and Thomson, DB and Davis, RF}, year={1999}, month={Aug}, pages={989–991} }
 @article{smith_davis_liu_kim_carpenter_1999, title={Microstructure, electrical properties, and thermal stability of Ti-based ohmic contacts to n-GaN}, volume={14}, ISSN={["2044-5326"]}, DOI={10.1557/JMR.1999.0137}, abstractNote={Single Ti layers, single TiN layers, and thin Ti films overlayered with Au were investigated as ohmic contacts to n-type (n 4.5 × 1017 to 7.4 × 1018 cm−3) single-crystal GaN (0001) films. Transmission line measurements (TLM) revealed the as-deposited TiN and Au/Ti contacts on n = 1.2 − 1018 cm−3 to be ohmic with room-temperature specific contact resistivities of 650 and 2.5 × 107minus;5 Ω cm2, respectively. Single Ti layer contacts had high resistance and were weakly rectifying in the as-deposited condition. The three contact/GaN systems exhibited a substantial decrease in resistivity after annealing; the value of ρc was also a function of the carrier concentration in the GaN. The Au/Ti contacts exhibited the lowest resistivity values yet observed in these contact studies, particularly for the more lightly doped n-GaN. The ρc for n = 1.2 × 1018 cm−3 reached 1.2 × 1026 Ω cm2; for n = 4.5 × 1017 cm−3, ρc = 7.5 × 1025 Ω cm2 after annealing both samples through 900 °C. X-ray photoelectron spectroscopy (XPS) and high-resolution cross-sectional transmission electron microscopy (X-TEM) analysis revealed the formation of TiN at the interface of annealed Ti layers in contact with GaN, which is believed to be beneficial for ohmic contact performance on n-GaN.}, number={3}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Smith, LL and Davis, RF and Liu, RJ and Kim, MJ and Carpenter, RW}, year={1999}, month={Mar}, pages={1032–1038} }
 @article{kaminska_piotrowska_jasinski_kozubowski_barcz_golaszewska_thomson_davis_bremser_1999, title={Ni/Si-based contacts to GaN: Thermally activated structural transformations leading to ohmic behavior}, volume={4S1}, number={G9.9}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Kaminska, E. and Piotrowska, A. and Jasinski, J. and Kozubowski, J. and Barcz, A. and Golaszewska, K. and Thomson, D. B. and Davis, R. F. and Bremser, M. D.}, year={1999} }
 @article{chao_stagarescu_downes_ryan_smith_hanser_bremser_davis_1999, title={Observation of highly dispersive surface states on GaN(0001)1x1}, volume={59}, number={24}, journal={Physical Review. B, Condensed Matter and Materials Physics}, author={Chao, Y. C. and Stagarescu, C. B. and Downes, J. E. and Ryan, P. and Smith, K. E. and Hanser, D. and Bremser, M. D. and Davis, R. F.}, year={1999}, pages={R15586–15589} }
 @article{gehrke_linthicum_thomson_rajagopal_batchelor_davis_1999, title={Pendeo-epitaxy of gallium nitride and aluminum nitride films and heterostructures on silicon carbide substrate}, volume={4S1}, number={G3.2}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Gehrke, T. and Linthicum, K. J. and Thomson, D. B. and Rajagopal, P. and Batchelor, A. D. and Davis, R. F.}, year={1999} }
 @article{linthicum_gehrke_thomson_carlson_rajagopal_smith_batchelor_davis_1999, title={Pendeo-epitaxy of gallium nitride thin films}, volume={75}, DOI={10.1063/1.124317}, abstractNote={Pendeoepitaxy, a form of selective lateral growth of GaN thin films has been developed using GaN/AlN/6H–SiC(0001) substrates and produced by organometallic vapor phase epitaxy. Selective lateral growth is forced to initiate from the (112̄0) GaN sidewalls of etched GaN seed forms by incorporating a silicon nitride seed mask and employing the SiC substrate as a pseudomask. Coalescence over and between the seed forms was achieved. Transmission electron microscopy revealed that all vertically threading defects stemming from the GaN/AlN and AlN/SiC interfaces are contained within the seed forms and a substantial reduction in the dislocation density of the laterally grown GaN. Atomic force microscopy analysis of the (112̄0) face of discrete pendeoepitaxial structures revealed a root mean square roughness of 0.98 Å. The pendeoepitaxial layer photoluminescence band edge emission peak was observed to be 3.454 eV and is blueshifted by 12 meV as compared to the GaN seed layer.}, number={2}, journal={Applied Physics Letters}, author={Linthicum, K. J. and Gehrke, T. and Thomson, D. B. and Carlson, E. P. and Rajagopal, P. and Smith, T. and Batchelor, D. and Davis, R.}, year={1999}, pages={196–198} }
 @misc{zheleva_smith_thomson_linthicum_rajagopal_davis_1999, title={Pendeo-epitaxy: A new approach for lateral growth of gallium nitride films}, volume={28}, number={4}, journal={Journal of Electronic Materials}, author={Zheleva, T. S. and Smith, S. A. and Thomson, D. B. and Linthicum, K. J. and Rajagopal, P. and Davis, R. F.}, year={1999}, pages={L5–8} }
 @article{zheleva_smith_thomson_gehrke_linthicum_rajagopal_carlson_ashmawi_davis_1999, title={Pendeo-epitaxy: A new approach for lateral growth of gallium nitride structures}, volume={4S1}, number={G3.38}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Zheleva, T. S. and Smith, S. A. and Thomson, D. B. and Gehrke, T. and Linthicum, K. J. and Rajagopal, P. and Carlson, E. and Ashmawi, W. M. and Davis, R. F.}, year={1999} }
 @article{bergman_alexson_nemanich_dutta_stroscio_balkas_davis_1999, title={Phonon dynamics and lifetimes of AlN and GaN crystallites}, volume={4S1}, DOI={10.1557/s1092578300003422}, abstractNote={The quasi-LO and quasi-TO modes of AlN crystallite were investigated. The analysis indicates that the Raman mode behavior concurs with Loudons’ model of mode-mixing in wurtzite (WZ) structure crystals which is due to the long-range electrostatic field. Phononlifetimes of GaN and AlN crystallites were studied via Raman lineshape. It was found that the low energy E2 mode lifetime is about an order of magnitude longer than that of the other modes, and that impurities impact significantly the phonon-lifetimes.}, number={G6.65}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Bergman, L. and Alexson, D. and Nemanich, R. J. and Dutta, M. and Stroscio, M. A. and Balkas, C. and Davis, R. F.}, year={1999} }
 @article{linthicum_gehrke_thomson_tracy_carlson_smith_zheleva_zorman_mehregany_davis_1999, title={Process routes for low defect-density GaN on various substrates employing pendeo-epitaxial growth techniques}, volume={4S1}, number={G4.9}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Linthicum, K. J. and Gehrke, T. and Thomson, D. B. and Tracy, K. M. and Carlson, E. P. and Smith, T. P. and Zheleva, T. S. and Zorman, C. A. and Mehregany, M. and Davis, R. F.}, year={1999} }
 @article{bergman_alexson_murphy_nemanich_dutta_stroscio_balkas_shin_davis_1999, title={Raman analysis of phonon lifetimes in AlN and GaN of wurtzite structure}, volume={59}, ISSN={["1550-235X"]}, DOI={10.1103/physrevb.59.12977}, abstractNote={Raman analyses of the lifetimes of phonons in GaN and AlN crystallites of wurtzite structure are presented. In order to ensure the accuracy of the measurement of the phonon lifetimes, an experimental procedure to eliminate the broadening due to the finite slit width was performed. The lifetime analyses indicate that the phonon lifetimes in AlN as well as in GaN fall into two main time regimes: a relatively long time of the ${E}_{2}^{1}$ mode and much shorter times of the ${E}_{2}^{2},$ $E1(\mathrm{TO}),$ and $A1(\mathrm{TO})$ modes. The lifetimes of the ${E}_{2}^{1},$ ${E}_{2}^{2},$ $E1(\mathrm{TO}),$ $A1(\mathrm{TO}),$ and $A1(\mathrm{LO})$ modes of an high-quality AlN crystallite are 4.4, 0.83, 0.91, 0.76, and 0.45 ps, respectively. Moreover, the lifetime of the $A1(\mathrm{LO})$ mode found in this study is consistent with the current phonon-decay model of that mode in wurtzite structure materials. The lifetimes of ${E}_{2}^{1},$ ${E}_{2}^{2},$ $E1(\mathrm{TO}),$ and $A1(\mathrm{TO})$ of a GaN crystallite were found to be 10.1, 1.4, 0.95, and 0.46 ps, respectively. The $A1(\mathrm{LO})$ mode in the GaN was not observed and its absence is attributed to plasmon damping. The lifetime shortening due to impurities was also studied: the lifetimes of the Raman modes of an AlN crystallite, which contains about two orders of magnitude more Si and C impurities relative to the concentration of the high-quality crystallite were found to be 50% shorter.}, number={20}, journal={PHYSICAL REVIEW B}, author={Bergman, L and Alexson, D and Murphy, PL and Nemanich, RJ and Dutta, M and Stroscio, MA and Balkas, C and Shin, H and Davis, RF}, year={1999}, month={May}, pages={12977–12982} }
 @article{bergman_dutta_balkas_davis_christman_alexson_nemanich_1999, title={Raman analysis of the E1 and A1 quasi-longitudinal optical and quasi-transverse optical modes in wurtzite AlN}, volume={85}, ISSN={["0021-8979"]}, DOI={10.1063/1.369712}, abstractNote={This article presents a study of the quasi-longitudinal optical and quasi-transverse optical modes in wurtzite AlN which originate from the interaction of phonons belonging to the A1 and E1 symmetry groups. In order to analyze the allowed quasi as well as pure Raman modes, the modes were observed in a rotating crystallographic coordinate system, and the Raman tensors of the wurtzite crystal structure were calculated as a function of the crystallographic rotation. The frequencies of the quasimodes of wurtzite AlN were also analyzed in terms of the interaction of the polar phonons with the long range electrostatic field model. The experimental values of the Raman frequencies of the quasiphonons concur with these expected from the model, implying that the long range electrostatic field dominates the short range forces for polar phonons in AlN.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Bergman, L and Dutta, M and Balkas, C and Davis, RF and Christman, JA and Alexson, D and Nemanich, RJ}, year={1999}, month={Apr}, pages={3535–3539} }
 @article{thomson_gehrke_linthicum_rajagopal_davis_1999, title={Ranges of deposition temperatures applicable for metalorganic vapor phase epitaxy of GaN films via the technique of pendeo- epitaxy}, volume={4S1}, number={G3.37}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Thomson, D. B. and Gehrke, T. and Linthicum, K. J. and Rajagopal, P. and Davis, R. F.}, year={1999} }
 @article{edwards_batchelor_buyanova_madsen_bremser_davis_aspnes_monemar_1999, title={Relaxation phenomena in GaN/ AlN/ 6H-SiC heterostructures}, volume={4S1}, DOI={10.1557/s1092578300002830}, abstractNote={We have developed a method to modulate the strain state (normally > 4 kbar, tensile) of moderately thick (∼2 μm) GaN based structures grown on 6H-SiC to a range 0 to -2 kbar of compressive stresses by introducing a strain-mediating layer (SML) above the standard high-temperature AlN buffer layer. The strain characteristics of subsequently deposited nitride layers can be modulated by changing the growth parameters of the SML layer. This is achieved by in-situ techiniques during crystal growth without degrading the optical and structural properties of the deposited layers.}, number={G3.78}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Edwards, N. V. and Batchelor, A. D. and Buyanova, I. A. and Madsen, L. D. and Bremser, M. D. and Davis, R. F. and Aspnes, D. E. and Monemar, B.}, year={1999} }
 @article{danielsson_zetterling_ostling_breitholtz_linthicum_thomson_nam_davis_1999, title={Simulation and electrical characterization of GaN/SiC and AlGaN/SiC heterodiodes}, volume={61-2}, number={1999 July 30}, journal={Materials Science & Engineering. B, Solid-state Materials for Advanced Technology}, author={Danielsson, E. and Zetterling, C. M. and Ostling, M. and Breitholtz, B. and Linthicum, K. and Thomson, D. B. and Nam, O. H. and Davis, R. F.}, year={1999}, pages={320–324} }
 @article{bidnyk_little_schmidt_cho_krasinski_song_goldenberg_yang_perry_bremser_et al._1999, title={Stimulated emission in GaN thin films in the temperature range of 300-700 K}, volume={85}, ISSN={["1089-7550"]}, DOI={10.1063/1.369325}, abstractNote={We report the results of an experimental study on stimulated and spontaneous emission from high-quality single-crystal GaN films grown on 6H-SiC and (0001) sapphire substrates in the temperature range of 300–700 K. We observed edge-emitted stimulated emission (SE) at temperatures as high as 700 K for samples grown on both SiC and sapphire substrates. The energy position of the SE and spontaneous emission peaks were shown to shift linearly to longer wavelengths with temperature and empirical expressions for the energy positions are given. We demonstrate that the energy separation between the spontaneous and SE peaks gradually increases from 90 meV at 300 K to 200 meV at 700 K indicating that an electron-hole plasma is responsible for the SE mechanism in this temperature range. The temperature sensitivity of the SE threshold for different samples was studied and the characteristic temperature was found to be 173 K in the temperature range of 300–700 K for one of the samples studied. We suggest that the unique properties of SE in GaN thin films at high temperatures could potentially be utilized in optoelectronic devices.}, number={3}, journal={JOURNAL OF APPLIED PHYSICS}, author={Bidnyk, S and Little, BD and Schmidt, TJ and Cho, YH and Krasinski, J and Song, JJ and Goldenberg, B and Yang, W and Perry, WG and Bremser, MD and et al.}, year={1999}, month={Feb}, pages={1792–1795} }
 @article{zheleva_ashmawi_nam_davis_1999, title={Thermal mismatch stress relaxation via lateral epitaxy in selectively grown GaN structures}, volume={74}, ISSN={["0003-6951"]}, DOI={10.1063/1.123017}, abstractNote={A reduction in the dislocation density of 104–105 cm−2 has been achieved via lateral epitaxial overgrowth (LEO) of GaN films selectively grown from stripes etched in SiO2 masks deposited on GaN/AlN/6H–SiC(0001) heterostructures. The magnitudes and distribution of stresses generated in the LEO GaN layer and the SiO2, due primarily to differences in the coefficients of thermal expansion, were modeled using finite element (FE) analysis. These calculations showed that localized compressive stress fields of ≈3 GPa occurred at the edges of the LEO GaN in the vicinity of the GaN/SiO2 interface. Localized compression along the GaN substrate/SiO2 interface and tension along the 〈0001〉 direction were responsible for the change in shape of the SiO2 stripes from rectangular with flat sides to an airfoil shape with curved sides. The FE calculations also revealed that an increase in the width of the LEO GaN regions over the SiO2 or the reduction in the separation between the GaN stripes (all other dimensions being fixed) resulted in a slight reduction in the compressive stresses along the LEO GaN/SiO2 interface and an increase in the compressive stress along [0001]. An increase in the shear stress, at the corners of the LEO GaN near the LEO GaN/SiO2 interface, with an increase in the width of the LEO GaN region were also indicated.}, number={17}, journal={APPLIED PHYSICS LETTERS}, author={Zheleva, TS and Ashmawi, WM and Nam, OH and Davis, RF}, year={1999}, month={Apr}, pages={2492–2494} }
 @article{king_davis_ronning_nemanich_1999, title={Valence band discontinuity of the (0001) 2H-GaN/(111) 3C-SiC interface}, volume={28}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-999-0145-4}, number={12}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={King, SW and Davis, RF and Ronning, C and Nemanich, RJ}, year={1999}, month={Dec}, pages={L34–L37} }
 @article{king_davis_ronning_benjamin_nemanich_1999, title={Valence band discontinuity, surface reconstruction, and chemistry of (0001), (000(1)over-bar), and (1(1)over-bar-00) 2H-AlN/6H-SiC interfaces}, volume={86}, ISSN={["0021-8979"]}, DOI={10.1063/1.371391}, abstractNote={A detailed examination of the valence band discontinuity (ΔEv) formed at the (0001), (0001̄), and (11̄00) interfaces between 2H–AlN and 6H–SiC has been conducted using x-ray and UV photoelectron spectroscopies. The ΔEv was observed to range from 0.6–2.0 eV depending on the growth direction (i.e., AlN on SiC vs SiC on AlN), as well as the crystallographic orientation, cut of the SiC substrate (i.e., on versus off axis), and SiC surface reconstruction and stoichiometry. A ΔEv of 1.4–1.5 eV was observed for AlN grown on (3×3) (0001)Si6H–SiC on-axis substrates; a ΔEv of 0.9–1.0 eV was observed for off-axis substrates with the same surface reconstruction. The values of ΔEv for AlN grown on (√3×√3)R30°(0001) 6H–SiC on-and-off-axis substrates were 1.1–1.2 eV. A larger valence band discontinuity of 1.9–2.0 eV was determined for 3C–SiC grown on (0001) 2H–AlN. Smaller values of ΔEv of 0.6–0.7 and 0.8–0.9 eV were observed for AlN grown on on-axis (0001̄)C and (11̄00)6H–SiC substrates, respectively.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, SW and Davis, RF and Ronning, C and Benjamin, MC and Nemanich, RJ}, year={1999}, month={Oct}, pages={4483–4490} }
 @article{king_nemanich_davis_1999, title={Wet chemical processing of (0001)(Si) 6H-SiC hydrophobic and hydrophilic surfaces}, volume={146}, ISSN={["0013-4651"]}, DOI={10.1149/1.1391864}, abstractNote={The wetting characteristics of polished or polished and thermally oxidized, on- and off-axis (0001) Si 6H-SiC [the silicon-terminated surface of SiC] surfaces in selected acids and bases have been determined and compared with that of (111)Si. Auger electron and X-ray photoelectron spectroscopies and low energy electron diffraction were used to characterize the chemical state and order of these surfaces. The oxidized SiC surfaces were hydrophilic after oxide removal with a 10:1 HF solution and were terminated with approximately a monolayer containing OH, CO, CH, and F species. The same effects were observed for the similarly treated (0001) C [the carbon-terminated surface of SiC], (1120), and (1010) surfaces. The as-polished SiC surfaces were hydrophobic and covered with a thin (5-10 A) contamination layer composed primarily of C-C, C-F, and Si-F bonded species. Removal of this layer using an RCA SC etch or Piranha clean resulted in a disordered hydrophilic SiC surface. A 20 A amorphous Si capping layer both passivated the SiC surfaces and provided a better alternative to the aforementioned contamination layer for producing hydrophobic surfaces on this material.}, number={5}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={King, SW and Nemanich, RJ and Davis, RF}, year={1999}, month={May}, pages={1910–1917} }
 @article{king_carlson_therrien_christman_nemanich_davis_1999, title={X-ray photoelectron spectroscopy analysis of GaN/(0001)AlN and AlN/(0001)GaN growth mechanisms}, volume={86}, ISSN={["0021-8979"]}, DOI={10.1063/1.371564}, abstractNote={The mechanisms of growth of GaN on AlN and AlN on GaN via gas source-molecular beam epitaxy with NH3 as the nitrogen source have been investigated using x-ray photoelectron spectroscopy, low energy electron diffraction, and Auger electron spectroscopy. The growth of GaN on AlN at low temperatures (650–750 °C) occurs via a Stranski–Krastanov 2D→3D type mechanism with the transition to 3D growth occurring at ≈10–15 Å. The mechanism changes to Frank van der Merwe (FM)/layer-by-layer growth above 800 °C. The growth of AlN on GaN occurred via a FM layer-by-layer mechanism within the 750–900 °C temperature range investigated. We propose a model based on the interaction of ammonia and atomic hydrogen with the GaN/AlN surfaces which indicates that the surface kinetics of hydrogen desorption and ammonia decomposition are the factors that determine the GaN growth mechanism.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, SW and Carlson, EP and Therrien, RJ and Christman, JA and Nemanich, RJ and Davis, RF}, year={1999}, month={Nov}, pages={5584–5593} }
 @article{ade_yang_english_hartman_davis_nemanich_litvinenko_pinayev_wu_madey_1998, title={A free electron laser-photoemission electron microscope system (FEL-PEEM)}, volume={5}, ISSN={["0218-625X"]}, DOI={10.1142/S0218625X98001596}, abstractNote={ We report first results from our effort to couple a high resolution photoemission electron microscope (PEEM) to the OK-4 ultraviolet free electron laser at Duke University (OK-4/Duke UV FEL). The OK-4/Duke UV FEL is a high intensity source of tunable monochromatic photons in the 3–10 eV energy range. This tunability is unique and allows us to operate near the photoemission threshold of any samples and thus maximize sample contrast while keeping chromatic berrations in the PEEM minimal. We have recorded first images from a variety of samples using spontaneous radiation from the OK-4/ Duke UV FEL in the photon energy range of 4.0–6.5 eV. Due to different photothreshold emission from different sample areas, emission from these areas could be turned on (or off) selectively. We have also observed relative intensity reversal with changes in photon energy which are interpreted as density-of-state contrast. Usable image quality has been achieved, even though the output power of the FEL in spontaneous emission mode was several orders of magnitude lower than the anticipated full laser power. The PEEM has achieved a spatial resolution of 12 nm. }, number={6}, journal={SURFACE REVIEW AND LETTERS}, author={Ade, H and Yang, W and English, SL and Hartman, J and Davis, RF and Nemanich, RJ and Litvinenko, VN and Pinayev, IV and Wu, Y and Madey, JMJ}, year={1998}, month={Dec}, pages={1257–1268} }
 @article{bremser_perry_nam_griffis_loesing_ricks_davis_1998, title={Acceptor and donor doping of AlxGa1-xN thin film alloys grown on 6H-SiC(0001) substrates via metalorganic vapor phase epitaxy}, volume={27}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-998-0392-9}, number={4}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Bremser, MD and Perry, WG and Nam, OH and Griffis, DP and Loesing, R and Ricks, DA and Davis, RF}, year={1998}, month={Apr}, pages={229–232} }
 @article{kern_rowland_tanaka_davis_1998, title={Aluminum nitride-silicon carbide solid solutions grown by plasma-assisted, gas-source molecular beam epitaxy}, volume={13}, ISSN={["0884-2914"]}, DOI={10.1557/JMR.1998.0257}, abstractNote={Solid solutions of aluminum nitride (AlN) and silicon carbide (SiC) have been grown at 900–1300 °C on vicinal α (6H)-SiC(0001) substrates by plasma-assisted, gas-source molecular beam epitaxy. Under specific processing conditions, films of (AlN)x(SiC) 1−x with 0.2 ≤ x ≤ 0.8, as determined by Auger electron spectrometry (AES), were deposited. Reflection high-energy electron diffraction (RHEED) was used to determine the crystalline quality, surface character, and epilayer polytype. Analysis of the resulting surfaces was also performed by scanning electron microscopy (SEM). High-resolution transmission electron microscopy (HRTEM) revealed that monocrystalline films with x ≥ 0.25 had the wurtzite (2H) crystal structure; however, films with x < 0.25 had the zincblende (3C) crystal structure.}, number={7}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Kern, RS and Rowland, LB and Tanaka, S and Davis, RF}, year={1998}, month={Jul}, pages={1816–1822} }
 @article{hanser_wolden_perry_zheleva_carlson_banks_therrien_davis_1998, title={Analysis of reactor geometry and diluent gas flow effects on the metalorganic vapor phase epitaxy of AlN and GaN thin films on alpha(6H)-SiC substrates}, volume={27}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-998-0394-7}, number={4}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Hanser, AD and Wolden, CA and Perry, WG and Zheleva, T and Carlson, EP and Banks, AD and Therrien, RJ and Davis, RF}, year={1998}, month={Apr}, pages={238–245} }
 @article{perry_bremser_zheleva_linthicum_davis_1998, title={Biaxial strain in AlxGa1-xN/GaN layers deposited on 6H-SiC}, volume={324}, ISSN={["0040-6090"]}, DOI={10.1016/S0040-6090(97)01217-0}, abstractNote={AlxGa1−xN/GaN multilayers (x≤0.12) deposited on AlN(0001) buffer layer/6H-SiC(0001) substrate combinations have been investigated using high resolution X-ray diffraction. Rocking curves (ω) showed that the AlxGa1−xN layers in the main contained a reduced dislocation density relative to the underlying GaN layers. The line widths of the radial scans (2θ−ω) of the AlxGa1−xN layers increased as the Al mole fraction increased due to alloy broadening. The in-plane lattice constant (a) of the AlxGa1−xN layer for each sample was equivalent to that of the GaN layer, indicating the layers were coherently strained. The strain in the AlGaN layer was tensile for each sample. This was determined using high-resolution reciprocal space maps of the (015) and (024) planes which revealed that the AlxGa1−xN and GaN lattice points had the same value of the in-plane components of the reciprocal lattice vector (S̄‖). For higher Al mole fractions, the samples were severely cracked, indicating the strain in the AlxGa1−xN layers exceeded critical values.}, number={1-2}, journal={THIN SOLID FILMS}, author={Perry, WG and Bremser, MB and Zheleva, T and Linthicum, KJ and Davis, RF}, year={1998}, month={Jul}, pages={107–114} }
 @article{perry_bremser_davis_1998, title={Cathodoluminescence studies of the deep level emission bands of AlxGa1-xN films deposited on 6H-SiC(0001)}, volume={83}, ISSN={["0021-8979"]}, DOI={10.1063/1.366716}, abstractNote={A comprehensive study of the sub band-edge emission bands of AlxGa1−xN (0.06⩽x⩽1) thin films deposited on vicinal and on-axis 6H–SiC(0001) substrates is presented. At 4.2 K strong band-edge emission, ascribed to donor-bound excitons, shallow donor-shallow-acceptor pair emission, and a deep emission band associated with the “yellow” band of GaN, were observed via cathodoluminescence. The energy shift of the shallow donor-shallow-acceptor pair band with respect to the peak of the donor-bound excitons peak exhibited a less than one-to-one correspondence with increasing Al mole fraction due the increasing localization of either the shallow donor and/or shallow acceptor. The yellow band was observed for all compositions and exhibited a similar energy shift with respect to both the donor-bound excitons and the shallow donor-shallow-acceptor pair bands as the Al mole fraction increased, except for a brief decrease at x≈0.5. This decrease was attributed to a donor oxygen level which entered the band gap at approximately this composition. A strong, broad emission band observed at 3.25 eV at 295 K in AlN and commonly associated with oxygen impurities was shown to be closely related to the yellow band of GaN.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Perry, WG and Bremser, MB and Davis, RF}, year={1998}, month={Jan}, pages={469–475} }
 @article{gruss_zheleva_davis_watkins_1998, title={Characterization of zirconium nitride coatings deposited by cathodic arc sputtering}, volume={107}, ISSN={["0257-8972"]}, DOI={10.1016/S0257-8972(98)00584-2}, abstractNote={Polycrystalline ZrN coatings with a composition of 58.41 at.% Zr and 41.59 at.% N were deposited by cathodic arc evaporation on to Incoloy 825, Hastelloy C22 and Titanium Grade 12 metal substrates. Analyses of the coatings by scanning electron microscopy and Auger electron spectroscopy revealed the presence of 1–8-μm-diameter macroparticles composed of Zr metal. Compressive stresses of 4.06, 3.88 and 2.69 GPa were measured via X-ray diffraction in the coatings deposited on Inc., Hast. and Ti. substrates, respectively. Values for Young's modulus and hardness of 458 and 27.65 GPa, respectively, were obtained via nanoindentation. Studies of the interfacial chemistry via Auger electron spectroscopy and transmission electron microscopy revealed chemically abrupt interfaces and good compositional uniformity throughout the thickness of the zirconium nitride coatings.}, number={2-3}, journal={SURFACE & COATINGS TECHNOLOGY}, author={Gruss, KA and Zheleva, T and Davis, RF and Watkins, TR}, year={1998}, month={Sep}, pages={115–124} }
 @article{king_barnak_bremser_tracy_ronning_davis_nemanich_1998, title={Cleaning of AlN and GaN surfaces}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368814}, abstractNote={Successful ex situ and in situ cleaning procedures for AlN and GaN surfaces have been investigated and achieved. Exposure to HF and HCl solutions produced the lowest coverages of oxygen on AlN and GaN surfaces, respectively. However, significant amounts of residual F and Cl were detected. These halogens tie up dangling bonds at the nitride surfaces hindering reoxidation. The desorption of F required temperatures >850 °C. Remote H plasma exposure was effective for removing halogens and hydrocarbons from the surfaces of both nitrides at 450 °C, but was not efficient for oxide removal. Annealing GaN in NH3 at 700–800 °C produced atomically clean as well as stoichiometric GaN surfaces.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, SW and Barnak, JP and Bremser, MD and Tracy, KM and Ronning, C and Davis, RF and Nemanich, RJ}, year={1998}, month={Nov}, pages={5248–5260} }
 @article{yang_wolden_liu_schlesser_davis_prater_sitar_1998, title={Coalesced oriented diamond films on nickel}, volume={13}, ISSN={["0884-2914"]}, DOI={10.1557/JMR.1998.0157}, abstractNote={The growth of coalesced, highly oriented diamond films has been achieved on nickel substrates using a multistep process that consisted of (i) seeding the Ni surface with 0.5 μm diamond powder, (ii) annealing at 1100 °C in a hydrogen atmosphere, and (iii) growth at 900 °C in a mixture of hydrogen and 0.5% methane. Auger depth profile analysis of a sample quenched after the annealing stage showed the presence of significant amounts of carbon (6 at. %) close to the substrate surface and about 3 at.% deeper in the substrate. The loss of carbon into the substrate resulted in relatively low nucleation density. The addition of methane into the gas phase during the annealing stage proved very effective in compensating for the diffusion. An addition of 0.5% methane in the gas phase produced optimum results, as the nucleation density, orientation of diamond particles, and uniformity were substantially improved. Substrates nucleated under these conditions were grown out into coalesced, 30 μm thick films. Both (100) and (111) oriented films showed a high degree of orientation and Raman spectra obtained from these orientations showed intense and narrow diamond signature peaks with FWHM's of 5 and 8 cm-1, respectively.}, number={5}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Yang, PC and Wolden, CA and Liu, W and Schlesser, R and Davis, RF and Prater, JT and Sitar, Z}, year={1998}, month={May}, pages={1120–1123} }
 @article{king_ronning_davis_benjamin_nemanich_1998, title={Dependence of (0001) GaN/AlN valence band discontinuity on growth temperature and surface reconstruction}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368355}, abstractNote={X ray and ultraviolet photoelectron spectroscopies have been used to determine the heterojunction valence band discontinuity at the (0001) GaN/AlN interface. Type I discontinuity values of 0.5±0.2 eV were determined for GaN grown on AlN at 650 °C and 0.8±0.2 eV for GaN grown on AlN at 800 °C. These values are critically evaluated with respect to film quality, the results of other experimental studies, and theory.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, SW and Ronning, C and Davis, RF and Benjamin, MC and Nemanich, RJ}, year={1998}, month={Aug}, pages={2086–2090} }
 @article{ward_nam_hartman_english_mccarson_schlesser_sitar_davis_nemanich_1998, title={Electron emission characteristics of GaN pyramid arrays grown via organometallic vapor phase epitaxy}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368775}, abstractNote={Selective growth of arrays of silicon-doped GaN (Si:GaN) pyramids for field emitter applications has been achieved. The electron emission characteristics of these arrays has been measured using techniques such as field emission, field emission energy distribution analysis (FEED), photoemission electron microscopy (PEEM), and field emission electron microscopy (FEEM). The field emission current–voltage (I–V) results indicate an average threshold field as low as 7 V/μm for an emission current of 10 nA. It is suggested that the low threshold field value is a consequence of both the low work function of Si:GaN and the field enhancement of the pyramids. The results of the FEEM and FEED measurements indicate agreement with the field emission I–V characteristics. The FEED results indicate that the Si:GaN pyramids are conducting, and that no significant ohmic losses are present between the top contact to the array and the field emitting pyramids. The PEEM and FEEM images show that the emission from the arrays is uniform over a 150 μm field of view.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Ward, BL and Nam, OH and Hartman, JD and English, SL and McCarson, BL and Schlesser, R and Sitar, Z and Davis, RF and Nemanich, RJ}, year={1998}, month={Nov}, pages={5238–5242} }
 @article{nemanich_baumann_benjamin_nam_sowers_ward_ade_davis_1998, title={Electron emission properties of crystalline diamond and III-nitride surfaces}, volume={130}, ISSN={["0169-4332"]}, DOI={10.1016/s0169-4332(98)00140-8}, abstractNote={Wide bandgap semiconductors have the possibility of exhibiting a negative electron affinity (NEA) meaning that electrons in the conduction band are not bound by the surface. The surface conditions are shown to be of critical importance in obtaining a negative electron affinity. UV-photoelectron spectroscopy can be used to distinguish and explore the effect. Surface terminations of molecular adsorbates and metals are shown to induce an NEA on diamond. Furthermore, a NEA has been established for epitaxial AlN and AlGaN on 6H–SiC. Field emission measurements from flat surfaces of p-type diamond and AlN are similar, but it is shown that the mechanisms may be quite different. The measurements support the recent suggestions that field emission from p-type diamond originates from the valence band while for AlN on SiC, the field emission results indicate emission from the AlN conduction band. We also report PEEM (photo-electron emission microscopy) and FEEM (field electron emission microscopy) images of an array of nitride emitters.}, number={1998 June}, journal={APPLIED SURFACE SCIENCE}, author={Nemanich, RJ and Baumann, PK and Benjamin, MC and Nam, OH and Sowers, AT and Ward, BL and Ade, H and Davis, RF}, year={1998}, month={Jun}, pages={694–703} }
 @article{joshkin_parker_bedair_krasnobaev_cuomo_davis_suvkhanov_1998, title={Fine structure of near-band-edge photoluminescence in He+-irradiated GaN grown on SiC}, volume={72}, ISSN={["0003-6951"]}, DOI={10.1063/1.121474}, abstractNote={The effect of He ion implantation on the optical properties of epitaxial GaN-on-SiC was studied. We observed that He+ irradiation increases the relative intensity of the “blue emission” and resistivity of GaN films and decreases the intensity of the near-band-edge photoluminescence. Because the intensity of the main peak is drastically decreased, the fine structure of the near-band-edge photoluminescence in GaN after He+ irradiation was observed. From a comparison of observed sharp lines with photoluminescence peaks of GaN doped with oxygen, we conclude that oxygen can produce a complex, which is characterized by a strong localization of free carriers and a large lattice distortion. The zero-phonon line of this defect has energy close to the band-gap energy of GaN.}, number={22}, journal={APPLIED PHYSICS LETTERS}, author={Joshkin, VA and Parker, CA and Bedair, SM and Krasnobaev, LY and Cuomo, JJ and Davis, RF and Suvkhanov, A}, year={1998}, month={Jun}, pages={2838–2840} }
 @article{wolden_davis_sitar_prater_1998, title={Flat-flame diamond CVD: the effect of pressure and operating conditions for specific applications}, volume={7}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(97)00206-9}, abstractNote={The radial uniformity and scaleable nature of flat flames make them an attractive technique for diamond deposition The advantages of low-pressure operation relative to atmospheric operation are discussed with respect to reactor design, heat transfer considerations and flame stability. The thermochemistry and kinetics of flat flames are described in regard to process optimization. Examples are provided to describe how to tailor the low-pressure process for the following applications: morphology control for the production of <100> textured films, low-temperature deposition and the introduction of dopants.}, number={2-5}, journal={DIAMOND AND RELATED MATERIALS}, author={Wolden, CA and Davis, RF and Sitar, Z and Prater, JT}, year={1998}, month={Feb}, pages={133–138} }
 @misc{roberson_finello_banks_davis_1998, title={Growth of Fe3N films via chemical vapor deposition of iron acetylacetonate and anhydrous ammonia}, volume={326}, number={1-2}, journal={Thin Solid Films}, author={Roberson, S. L. and Finello, D. and Banks, A. D. and Davis, R. F.}, year={1998}, pages={47–50} }
 @article{roberson_finello_davis_1998, title={Growth of MoxN films via chemical vapor deposition of MoCl5 and NH3}, volume={102}, ISSN={["0257-8972"]}, DOI={10.1016/S0257-8972(98)00448-4}, abstractNote={Polycrystalline MoxN (x = 1 or 2) films have been grown via chemical vapor deposition on 50 μm thick polycrystalline Ti substrates using molybdenum pentachloride (MoCl5) and anhydrous ammonia (NH3) in a cold-wall vertical pancake-style reactor. X-ray diffraction data indicated that a two-phase MoxN assemblage consisting of γ-Mo2N and δ-MoN was present in films deposited above 400 °C. The percentages of γ-Mo2N and δ-MoN in the films decreased and increased, respectively, as the deposition temperature increased at constant NH3flow rates and deposition pressures. The surface macrostructure of the as-deposited films was independent of the deposition temperature and was very similar to that of the uncoated Ti substrate. However, the microstructure of the films varied with the deposition temperature. Energy dispersive X-ray data indicated that films deposited at and above 400 °C did not contain detectable levels of chlorine.}, number={3}, journal={SURFACE & COATINGS TECHNOLOGY}, author={Roberson, SL and Finello, D and Davis, RF}, year={1998}, month={Apr}, pages={256–259} }
 @article{jarrendahl_smith_zheleva_kern_davis_1998, title={Growth of highly (0001)-oriented aluminum nitride thin films with smooth surfaces on silicon carbide by gas-source molecular beam epitaxy}, volume={49}, ISSN={["0042-207X"]}, DOI={10.1016/S0042-207X(97)00177-2}, abstractNote={Aluminum nitride thin films with very smooth surfaces have been grown by gas-source molecular beam epitaxy on 4H and 6H silicon carbide substrates. High purity ammonia was used as the nitrogen source in conjunction with Al evaporated from an effusion cell. Streaked reflection high energy electron diffraction patterns and reconstructions of the AlN surfaces indicated smooth films. This surface character was confirmed via atomic force microscopy and transmission electron microscopy which showed roughness root mean square values typically below 1 nm and very flat surfaces, respectively. X-ray diffraction showed the films to be highly c-axis oriented and single phase. Major impurities in the AlN films were oxygen and carbon, as revealed by secondary ion mass spectrometry.}, number={3}, journal={VACUUM}, author={Jarrendahl, K and Smith, SA and Zheleva, T and Kern, RS and Davis, RF}, year={1998}, month={Mar}, pages={189–191} }
 @article{kaminska_piotrowska_jasinski_kozubowski_barcz_golaszewska_bremser_davis_1998, title={Interfacial microstructure of Ni/Si-based ohmic contacts to GaN}, volume={94}, ISSN={["0587-4246"]}, DOI={10.12693/APhysPolA.94.383}, abstractNote={Development of low-resistance, thermally stable ohmic contacts is one of the big challenges for the progress in the GaN device technology. We have recently reported on novel Ni/Si-based metallization systems providing ohmic contacts on GaN [1]. We have adopted the idea of Sands et al. [2] of the incorporation of a dopant into the semiconductor subcontact region by solid-phase dissolution and regrowth (SPR). To produce contacts to p-type GaN, Mg dopant is added to the Ni/Si metallization; for n-type GaN, Si is the intended donor dopant [1]. We have shown that these contacts exhibit ohmic behavior after annealing at temperatures ranging from 400 to 600°C, with resistivities of about 1 x 10 -3 Ω cm2 at p-type (p 3 x 10 17 cm-3) and n-type (n 2 x 10 17 cm-3) GaN. The preliminary characterization using Rutherford backscattering spectrometry (RBS), secondary ion mass spectrometry (SIMS), and X-ray diffraction (XRD) indicated that several thermally activated solid-phase processes take place during the formation of ohmic contacts. However, a full understanding of these processes and their influence on the metal/GaN interface properties is still lacking. This study will focus on microstructure of Ni/Si-based contacts. In order to investigate structural properties such aS interface abruptness, phase composition, and defects in the contact region we have applied crosS-sectional tran8mission}, number={3}, journal={ACTA PHYSICA POLONICA A}, author={Kaminska, E and Piotrowska, A and Jasinski, J and Kozubowski, J and Barcz, A and Golaszewska, K and Bremser, MD and Davis, RF}, year={1998}, month={Sep}, pages={383–386} }
 @article{shan_fischer_hwang_little_hauenstein_xie_song_kim_goldenberg_horning_et al._1998, title={Intrinsic exciton transitions in GaN}, volume={83}, ISSN={["0021-8979"]}, DOI={10.1063/1.366660}, abstractNote={Intrinsic excitonic transitions in GaN have been studied using a variety of spectroscopic measurements. Sharp spectral structures associated with intrinsic free excitons could be observed in photoluminescence, reflection, and absorption spectra. The energy positions of excitonic transitions in GaN epitaxial layers were found to be influenced by the residual strain resulting from lattice-parameter and thermal-expansion mismatches between the epilayers and the substrates. The values of the four principal deformation potentials of wurtzite GaN were derived by using the strain tensor components determined by x-ray measurements. The observation of spectral features involving the emission of LO phonons in absorption and photoluminescence excitation spectra at energies above exciton resonances indicate that a phonon-assisted indirect excitation process, which simultaneously generates a free exciton and a LO phonon, is a very significant and efficient process in GaN. The lifetime of the free excitons is found to be longer than the relaxation time of LO-phonon emission but much shorter than that of acoustic-phonon emission.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Shan, W and Fischer, AJ and Hwang, SJ and Little, BD and Hauenstein, RJ and Xie, XC and Song, JJ and Kim, SS and Goldenberg, B and Horning, R and et al.}, year={1998}, month={Jan}, pages={455–461} }
 @article{wisniewski_knap_malzac_camassel_bremser_davis_suski_1998, title={Investigation of optically active E-1 transversal optic phonon modes in AlxGa1-xN layers deposited on 6H-SiC substrates using infrared reflectance}, volume={73}, ISSN={["1077-3118"]}, DOI={10.1063/1.122273}, abstractNote={We report an investigation, performed in the full composition range x=0–1, of the change in infrared reflectivity spectra of AlxGa1−xN layers deposited on 6H–SiC substrates. We have found two different transverse E1(TO) phonon frequencies that can be assigned to AlN-like and GaN-like modes. The composition dependences of these frequencies can be well approximated by linear functions and the oscillator strengths scale like the corresponding Al and Ga mole fractions, respectively. On a purely experimental basis, this establishes evidence of a two-mode behavior for this controversial alloy system. The frequencies of the impurity mode of Ga in AlN (622 cm−1) and of the impurity mode of Al in GaN (643 cm−1) were determined.}, number={13}, journal={APPLIED PHYSICS LETTERS}, author={Wisniewski, P and Knap, W and Malzac, JP and Camassel, J and Bremser, MD and Davis, RF and Suski, T}, year={1998}, month={Sep}, pages={1760–1762} }
 @article{nam_zheleva_bremser_davis_1998, title={Lateral epitaxial overgrowth of GaN films on SiO2 areas via metalorganic vapor phase epitaxy}, volume={27}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-998-0393-8}, number={4}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Nam, OH and Zheleva, TS and Bremser, MD and Davis, RF}, year={1998}, month={Apr}, pages={233–237} }
 @article{dalmer_restle_sebastian_vetter_hofsass_bremser_ronning_davis_wahl_bharuth-ram_1998, title={Lattice site location studies of ion implanted Li-8 in GaN}, volume={84}, ISSN={["1089-7550"]}, DOI={10.1063/1.368463}, abstractNote={The lattice sites of ion implanted Li atoms in GaN were studied as a function of implantation temperature between room temperature and 770 K. We measured the channeling and blocking patterns of α-particles emitted in the radioactive decay of implanted Li8 ions to determine the Li lattice sites. Below 700 K Li atoms occupy mainly interstitial sites in the center of the c-axis hexagons at positions c/4 and 3c/4, where c is the lattice constant in c-axis direction. Around 700 K Li starts to diffuse and presumably interacts with vacancies created in the implantation process. This leads to the formation of substitutional Li above 700 K. An activation energy of about 1.7 eV for interstitial Li diffusion was determined.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Dalmer, M and Restle, M and Sebastian, M and Vetter, U and Hofsass, H and Bremser, MD and Ronning, C and Davis, RF and Wahl, U and Bharuth-Ram, K}, year={1998}, month={Sep}, pages={3085–3089} }
 @article{jarrendahl_davis_1998, title={Materials properties and characterization of SiC}, volume={52}, ISBN={["0-12-752160-7"]}, ISSN={["0080-8784"]}, DOI={10.1016/S0080-8784(08)62843-4}, abstractNote={This chapter discusses the materials properties and characterization of silicon carbide (Sic). Wide energy bandgaps, high thermal conductivity, high-saturated electron drift velocities, and high-breakdown electric fields make Sic a candidate of choice for high-temperature, high-speed, high-frequency, and high-power applications. In a polytypic compound, similar sheets of atoms or symmetrical variants are stacked atop each other and related according to a symmetry operator. The most stable way to stack an identical second sheet of close-packed spheres is to place the spheres atop the valleys in the first sheet. The Sic polytypes can be n-type doped using nitrogen or phosphorus as donors and p-type using boron, aluminum, or gallium as acceptors. In general, unintentionally doped Sic has n-type conductivity because of nitrogen donors included as a contaminant during the production of the material. The electron and hole mobilities in Sic are a function of the nature of the material (carrier concentration, polytype, structural quality) and temperature.}, journal={SIC MATERIALS AND DEVICES}, author={Jarrendahl, K and Davis, RF}, year={1998}, pages={1–20} }
 @article{roberson_finello_davis_1998, title={Microstructural factors influencing the properties of high surface area molybdenum nitride films converted from molybdenum trioxide films deposited via solution spray pyrolysis}, volume={13}, ISSN={["0884-2914"]}, DOI={10.1557/JMR.1998.0313}, abstractNote={Molybdenum trioxide (MoO3) films, 15 µm thick, have been deposited on 50 µm thick polycrystalline titanium substrates from 250 to 500 °C via liquid spray pyrolysis. Molybdenum pentachloride (MoCl5) dissolved in methanol was used as the molybdenum source; ambient conditions provided the oxygen source. X-ray diffraction (XRD) data indicated that amorphous MoO3 films were produced at deposition temperatures below 400 °C. Randomly orientated polycrystalline MoO3 films were produced at 400 °C and higher deposition temperatures. The deposition temperature also influenced the surface area of the films and their average grain size. Subsequent conversion of the MoO3 films to high surface area (HSA) conductive films containing both γ–Mo2N and δ–MoN was accomplished via programmed reactions with anhydrous NH3 and involved the formation of MoO2 and MoOxN1−x as intermediate phases. The degree of crystallinity, surface area, and average grain size of the MoO3 films strongly influenced the average grain size and surface area of the resultant MoxN films.}, number={8}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Roberson, SL and Finello, D and Davis, RF}, year={1998}, month={Aug}, pages={2237–2244} }
 @article{ronning_carlson_thomson_davis_1998, title={Optical activation of Be implanted into GaN}, volume={73}, ISSN={["0003-6951"]}, DOI={10.1063/1.122225}, abstractNote={Single crystalline (0001) gallium nitride layers were implanted with beryllium. Photoluminescence (PL) measurements were subsequently performed as a function of implantation dose and annealing temperature. One new line in the PL spectra at 3.35 eV provided strong evidence for the presence of optically active Be acceptors and has been assigned to band–acceptor (eA) recombinations. The determined ionization energy of 150±10 meV confirmed that isolated Be has the most shallow acceptor level in GaN. Co-implantation of nitrogen did not enhance the activation of the Be acceptors.}, number={12}, journal={APPLIED PHYSICS LETTERS}, author={Ronning, C and Carlson, EP and Thomson, DB and Davis, RF}, year={1998}, month={Sep}, pages={1622–1624} }
 @article{freitas_nam_zheleva_davis_1998, title={Optical and structural properties of lateral epitaxial overgrown GaN layers}, volume={190}, number={1998 June}, journal={Journal of Crystal Growth}, author={Freitas, J. A. and Nam, O. H. and Zheleva, T. S. and Davis, R. F.}, year={1998}, pages={92–96} }
 @article{freitas_nam_davis_saparin_obyden_1998, title={Optical characterization of lateral epitaxial overgrown GaN layers}, volume={72}, ISSN={["0003-6951"]}, DOI={10.1063/1.121517}, abstractNote={The optical properties of homoepitaxial GaN layers deposited by organometallic vapor phase epitaxy on stripe-patterned GaN films on 6H-SiC substrates have been investigated. Analysis of the spatially-resolved Raman scattering spectra indicate an improvement in material quality of the overgrown region. Room-temperature color cathodoluminescence imaging and low-temperature photoluminescence measurements indicate that a donor and an acceptor, different from those detected in the underlying GaN/AlN/SiC substrate, have been incorporated in the epitaxial layer. Detailed photoluminescence studies of the near-band-edge emission strongly suggest that Si is the additional donor detected in the homoepitaxial GaN layer. Its occurrence, along with that of an acceptor-related defect which is primarily found in the laterally overgrown region, is discussed.}, number={23}, journal={APPLIED PHYSICS LETTERS}, author={Freitas, JA and Nam, OH and Davis, RF and Saparin, GV and Obyden, SK}, year={1998}, month={Jun}, pages={2990–2992} }
 @article{roberson_finello_davis_1998, title={Phase control of MoxN films via chemical vapor deposition}, volume={324}, ISSN={["0040-6090"]}, DOI={10.1016/S0040-6090(97)01202-9}, abstractNote={Polycrystalline single phase (γ-Mo2N and δ-MoN) and two phase (γ-Mo2N+δ-MoN) films have been deposited via chemical vapor deposition on prepared 50 μm thick polycrystalline Ti substrates using both molybdenum pentachloride (MoCl5) and molybdenum hexacarbonyl (Mo(CO)6), diluted in either N2 or Ar, and anhydrous ammonia (NH3) in a cold-wall, vertical pancake-style reactor. X-ray diffraction data showed that polycrystalline, single phase γ-Mo2N films were deposited between 400–450°C with the MoCl5 precursor and between 350–500°C with the Mo(CO)6 precursor. Above these respective temperatures and up to 700°C, a two-phase mixture of γ-Mo2N and δ-MoN was observed. At 700°C, single phase δ-MoN films were deposited by employing the Mo(CO)6 precursor and 1.5 slm of NH3; however, a two phase mixture of ≈95 at.% δ-MoN and ≈5 at.% γ-Mo2N was observed in films prepared using the MoCl5 precursor. Regardless of the precursor, decreases in the NH3 flow rate were matched by decreases in δ-MoN percentages at each temperature where δ-MoN was present. Increasing in the deposition rate also resulted in decreasing δ-MoN percentages at each deposition temperature. Scanning electron micrographs (SEM) indicated that the porous microstructure of the films were dependent on both the deposition temperature and the precursor employed. Energy dispersive X-ray (EDX) data indicated that films deposited at and above 400°C with the MoCl5 precursor did not contain detectable levels of chlorine. Higher carbon levels were detected in films deposited with the Mo(CO)6 precursor than with the MoCl5 precursor.}, number={1-2}, journal={THIN SOLID FILMS}, author={Roberson, SL and Finello, D and Davis, RF}, year={1998}, month={Jul}, pages={30–36} }
 @article{nipko_loong_balkas_davis_1998, title={Phonon density of states of bulk gallium nitride}, volume={73}, ISSN={["0003-6951"]}, DOI={10.1063/1.121714}, abstractNote={We report the measured phonon density of states of a bulk GaN powder by time-of-flight neutron spectroscopy. The observed one-phonon excitation spectrum consists of two broad bands centered at about 23 and 39 meV corresponding to the acoustic and the first group of optical phonons; two sharp bands of upper optic modes at about 75 and 86 meV; and a gap of 45–65 meV. The phonon dispersion curves, lattice specific heat, and Debye temperature are calculated from fitting the data with a rigid-ion model.}, number={1}, journal={APPLIED PHYSICS LETTERS}, author={Nipko, JC and Loong, CK and Balkas, CM and Davis, RF}, year={1998}, month={Jul}, pages={34–36} }
 @misc{stutz_mack_bremser_nam_davis_look_1998, title={Photoelectrochemical capacitance-voltage measurements in GaN}, volume={27}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-998-0182-4}, number={5}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Stutz, CE and Mack, M and Bremser, MD and Nam, OH and Davis, RF and Look, DC}, year={1998}, month={May}, pages={L26–L28} }
 @article{jahnen_albrecht_dorsch_christiansen_strunk_hanser_davis_1998, title={Pinholes, dislocations and strain relaxation in InGaN}, volume={3}, number={39}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Jahnen, B. and Albrecht, M. and Dorsch, W. and Christiansen, S. and Strunk, H. P. and Hanser, D. and Davis, R. F.}, year={1998} }
 @article{kern_tanaka_rowland_davis_1998, title={Reaction kinetics of silicon carbide deposition by gas-source molecular-beam epitaxy}, volume={183}, number={4}, journal={Journal of Crystal Growth}, author={Kern, R. S. and Tanaka, S. and Rowland, L. B. and Davis, R. F.}, year={1998}, pages={581–593} }
 @article{edwards_yoo_bremser_horton_perkins_weeks_liu_stall_kuech_davis_et al._1998, title={Spectroscopic ellipsometry and low-temperature reflectance: complementary analysis of GaN thin films}, volume={313}, ISSN={["0040-6090"]}, DOI={10.1016/S0040-6090(97)00815-8}, abstractNote={Abstract We report spectroscopic ellipsometry (SE) and low-temperature reflectance data on epitaxial GaN thin-film samples covering the widest range of tensile and compressive stress (−3.8 to 3.5 kbar) thus far. SE allows us to assess the preparation of smooth and abrupt GaN surfaces by chemical treatments in real time, and, coupled with the reflectance data, the E d n /d E contribution to dispersion, which is important for laser action. The reflectance data explicitly show the non-linear behavior of the B-A and C-A splittings vs. the energy of the A exciton. Lineshape ambiguities that hindered previous interpretations have been resolved with reciprocal space analysis, allowing us to obtain band parameters such as Δ SO =17.0±1 meV and Δ CF =9.8±1 meV with increased confidence.}, number={1998 Feb.}, journal={THIN SOLID FILMS}, author={Edwards, NV and Yoo, SD and Bremser, MD and Horton, MN and Perkins, NR and Weeks, TW and Liu, H and Stall, RA and Kuech, TF and Davis, RF and et al.}, year={1998}, month={Feb}, pages={187–192} }
 @article{ronning_banks_mccarson_schlesser_sitar_davis_ward_nemanich_1998, title={Structural and electronic properties of boron nitride thin films containing silicon}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368752}, abstractNote={The incorporation of silicon into boron nitride films (BN:Si) has been achieved during ion beam assisted deposition growth. A gradual change from cubic boron nitride (c-BN) to hexagonal boron nitride (h-BN) was observed with increasing silicon concentration. Ultraviolet photoelectron spectroscopy, field emission, and field emission electron energy distribution experiments indicated that the observed electron transport and emission were due to hopping conduction between localized states in a band at the Fermi level for the undoped c-BN films and at the band tails of the valence band maximum for the BN:Si films. A negative electron affinity was observed for undoped c-BN films; this phenomenon disappeared upon silicon doping due to the transformation to h-BN. No shift of the Fermi level was observed in any BN:Si film; thus, n-type doping can be excluded.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Ronning, C and Banks, AD and McCarson, BL and Schlesser, R and Sitar, Z and Davis, RF and Ward, BL and Nemanich, RJ}, year={1998}, month={Nov}, pages={5046–5051} }
 @article{yang_liu_schlesser_wolden_davis_prater_sitar_1998, title={Surface melting in the heteroepitaxial nucleation of diamond on Ni}, volume={187}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(97)00854-3}, abstractNote={Surface melting associated with the heteroepitaxial nucleation of diamond on Ni was investigated. Scanning electron microscopy of quenched samples revealed flow patterns and a recrystallized surface morphology. A combination of techniques including in situ optical monitoring, differential thermal analysis, Auger depth profile analysis, and cross-section transmission electron microscopy (TEM) analysis were performed to identify the nature of the molten layer. Data obtained from different experiments were in good mutual agreement. All experimental results strongly indicated that a molten Ni–C–H surface layer was involved in the nucleation process. The presence of both carbon and atomic hydrogen played an important role in the depression of the melting point which was measured to be >300°C less than the melting point of pure Ni.}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Yang, PC and Liu, W and Schlesser, R and Wolden, CA and Davis, RF and Prater, JT and Sitar, Z}, year={1998}, month={Apr}, pages={81–88} }
 @article{roberson_finello_davis_1998, title={Synthesis of low oxygen concentration molybdenum nitride films}, volume={248}, number={1-2}, journal={Materials Science & Engineering. A, Structural Materials: Properties, Microstructure and Processing}, author={Roberson, S. L. and Finello, D. and Davis, R. F.}, year={1998}, pages={198–205} }
 @article{kawaguchi_shimizu_yamaguchi_hiramatsu_sawaki_taki_tsuda_kuwano_oki_zheleva_et al._1998, title={The formation of crystalline defects and crystal growth mechanism in InxGa1-xN/GaN heterostructure grown by metalorganic vapor phase epitaxy}, volume={190}, number={1998 June}, journal={Journal of Crystal Growth}, author={Kawaguchi, Y. and Shimizu, M. and Yamaguchi, M. and Hiramatsu, K. and Sawaki, N. and Taki, W. and Tsuda, H. and Kuwano, N. and Oki, K. and Zheleva, T. and et al.}, year={1998}, pages={24–28} }
 @article{liu_yang_wolden_davis_prater_sitar_1998, title={Transmission electron microscopy analysis of the oriented diamond growth on nickel substrates}, volume={83}, ISSN={["0021-8979"]}, DOI={10.1063/1.367885}, abstractNote={Transmission electron microscopy (TEM) was used to investigate the interfacial microstructure and the phases that developed during the nucleation and growth of oriented diamond on Ni by a hot filament process. Oriented Ni4C nuclei were identified by plan-view TEM in a sample quenched during the nucleation stage. Likewise, the presence of the Ni4C phase between the diamond and the Ni substrate was observed by cross-section TEM in samples grown for several hours. The orientational relationship among the diamond, Ni4C, and Ni substrate was examined by selected area diffraction. Diamond and Ni4C interfacial phase had a good epitaxial relationship, while the interfacial Ni4C phase and the Ni substrate developed with a small misfit and rotation. Based on these experimental results, the nucleation mechanism of oriented diamond growth on Ni is proposed.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Liu, W and Yang, PC and Wolden, CA and Davis, RF and Prater, JT and Sitar, Z}, year={1998}, month={Jun}, pages={7658–7663} }
 @article{edwards_bremser_davis_batchelor_yoo_karan_aspnes_1998, title={Trends in residual stress for GaN/AlN/6H-SiC heterostructures}, volume={73}, ISSN={["1077-3118"]}, DOI={10.1063/1.122597}, abstractNote={We discuss trends in residual stress as a function of film thickness, growth temperature, and substrate orientation for GaN/AlN/6H–SiC heterostructures. Films are mostly compressive for samples less than about 0.7 μm thick, are tensile up to about 2 μm, then abruptly become less tensile with stress values near 1 kbar thereafter. We interpret this as a successive relief of lattice mismatch and thermal stresses culminating in a catastrophic relief by unknown mechanisms at moderate thicknesses. These data indicate that relaxation processes in these heterostructures are not as well understood as previously supposed.}, number={19}, journal={APPLIED PHYSICS LETTERS}, author={Edwards, NV and Bremser, MD and Davis, RF and Batchelor, AD and Yoo, SD and Karan, CF and Aspnes, DE}, year={1998}, month={Nov}, pages={2808–2810} }
 @article{king_ronning_davis_busby_nemanich_1998, title={X-ray photoelectron diffraction from (3X3) and (root 3X root 3)R30 degrees (001)(Si) 6H-SiC surfaces}, volume={84}, ISSN={["1089-7550"]}, DOI={10.1063/1.368879}, abstractNote={High-resolution (±1°) x-ray photoelectron diffraction (XPD) patterns were obtained along high symmetry azimuths of the (3×3) and (√3×√3)R30° reconstructed (0001)Si 6H–SiC surfaces. The data were compared to XPD patterns obtained from (7×7) Si (111) as well as to models proposed for the (3×3) and (√3×√3)R30° 6H–SiC reconstructions. Forward scattering features similar to those observed from the (7×7) Si (111) were also observed from the (√3×√3)R30° 6H–SiC (0001)Si surface. Additional structures were found and attributed to the substitution of carbon atoms for silicon. Unlike (1×1) and (7×7) Si (111) surfaces, the XPD patterns of (3×3) and (√3×√3)R30° SiC (0001)Si surfaces are different which is due to the presence of an incomplete bilayer of Si on the (3×3) surface. The most significant difference with the Si system is the equivalence of the [101̄0] and [011̄0] azimuths in the (3×3) structure. These results are consistent with a faulted Si bilayer stacking sequence which was proposed based on scanning tunneling microscopy observations.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, SW and Ronning, C and Davis, RF and Busby, RS and Nemanich, RJ}, year={1998}, month={Dec}, pages={6042–6048} }
 @article{yang_schlesser_wolden_liu_davis_sitar_prater_1997, title={Control of diamond heteroepitaxy on nickel by optical reflectance}, volume={70}, ISSN={["0003-6951"]}, DOI={10.1063/1.118756}, abstractNote={Real time in situ laser reflectometry was used to investigate changes in surface morphology observed during the nucleation of oriented diamond on Ni in a hot filament chemical vapor deposition reactor. Characteristic features observed in the intensities of reflected and scattered light were interpreted by comparison with scanning electron micrographs of the diamond seeded substrates quenched at sequential stages of the process. Based on this analysis, a process was developed in which the scattered light signal was used as a steering parameter. Using this process, oriented nucleation and growth of diamond on Ni can be repeatedly achieved.}, number={22}, journal={APPLIED PHYSICS LETTERS}, author={Yang, PC and Schlesser, R and Wolden, CA and Liu, W and Davis, RF and Sitar, Z and Prater, JT}, year={1997}, month={Jun}, pages={2960–2962} }
 @article{kern_davis_1997, title={Deposition and doping of silicon carbide by gas-source molecular beam epitaxy}, volume={71}, ISSN={["0003-6951"]}, DOI={10.1063/1.119892}, abstractNote={Thin films of silicon carbide (SiC) have been deposited at 1400–1450 °C on vicinal and on-axis 6H-SiC(0001) substrates by gas-source molecular beam epitaxy using the SiH4-C2H4-H2 gas system. Polytype control (6H- or 3C-SiC) was established by utilizing substrates of particular orientations. Residual, unintentionally incorporated nitrogen impurity levels were affected by changing the SiH4/C2H4 gas flow ratio, in agreement with the “site-competition epitaxy” model. In situ doping was achieved by intentional introduction of nitrogen and aluminum into the growing crystal.}, number={10}, journal={APPLIED PHYSICS LETTERS}, author={Kern, RS and Davis, RF}, year={1997}, month={Sep}, pages={1356–1358} }
 @article{zheleva_nam_bremser_davis_1997, title={Dislocation density reduction via lateral epitaxy in selectively grown GaN structures}, volume={71}, ISSN={["0003-6951"]}, DOI={10.1063/1.120091}, abstractNote={The microstructure and the lateral epitaxy mechanism of formation of homoepitaxially and selectively grown GaN structures within windows in SiO2 masks have been investigated by transmission electron microscopy (TEM) and scanning electron microscopy. The structures were produced by organometallic vapor phase epitaxy for field emission studies. A GaN layer underlying the SiO2 mask provided the crystallographic template for the initial vertical growth of the GaN hexagonal pyramids or striped pattern. The SiO2 film provided an amorphous stage on which lateral growth of the GaN occurred and possibly very limited compliancy in terms of atomic arrangement during the lateral growth and in the accommodation of the mismatch in the coefficients of thermal expansion during cooling. Observations with TEM show a substantial reduction in the dislocation density in the areas of lateral growth of the GaN deposited on the SiO2 mask. In many of these areas no dislocations were observed.}, number={17}, journal={APPLIED PHYSICS LETTERS}, author={Zheleva, TS and Nam, OH and Bremser, MD and Davis, RF}, year={1997}, month={Oct}, pages={2472–2474} }
 @article{davis_paisley_sitar_kester_ailey_linthicum_rowland_tanaka_kern_1997, title={Gas-source molecular beam epitaxy of III-V nitrides}, volume={178}, ISSN={["1873-5002"]}, DOI={10.1016/S0022-0248(97)00077-8}, abstractNote={Abstract Amorphous, hexagonal and cubic phases of BN were grown via ion beam assisted deposition on Si(1 0 0) substrates. Gas-source molecular beam epitaxy of the III–V nitrides is reviewed. Sapphire(0 0 0 1) is the most commonly employed substrate with 6H-SiC(0 0 0 1), ZnO(1 1 1) and Si(1 1 1) also being used primarily for the growth of wurtzite GaN(0 0 0 1) in tandem with previously deposited GaN(0 0 0 1) or AlN(0 0 0 1) buffer layers. Silicon(0 0 1), GaAs(0 0 1), GaP(0 0 1) and 3C-SiC(0 0 1) have been employed for growth of cubic (zincblende) β-GaN(0 0 1). The precursor materials are evaporated metals and reactive N species produced either via ECR or RF plasma decomposition of N2 or from ammonia. However, point defect damage from the plasma-derived species has resulted in a steady increase in the number of investigators now using ammonia. The growth temperatures for wurtzite GaN have increased from 650 ± 50°C to 800 ± 50°C to enhance the surface mobility of the reactants and, in turn, the efficiency of decomposition of ammonia and the microstructure and the growth rate of the films. Doping has been achieved primarily with Si (donor) and Mg (acceptor); the latter has been activated without post-growth annealing. Simple heterostructures, a p-n junction LED and a modulation-doped field-effect transistor have been achieved using GSMBE-grown material.}, number={1-2}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Davis, RF and Paisley, MJ and Sitar, Z and Kester, DJ and Ailey, KS and Linthicum, K and Rowland, LB and Tanaka, S and Kern, RS}, year={1997}, month={Jun}, pages={87–101} }
 @article{kern_jarrendahl_tanaka_davis_1997, title={Growth and doping via gas-source molecular beam epitaxy of SiC and SiC/AlN heterostructures and their microstructural and electrical characterization}, volume={6}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(97)00066-6}, abstractNote={Gas-source molecular beam epitaxy has been employed to grown thin films of SiC and AlN on vicinal and on-axis 6H-SiC(0001). Growth using the SiH4C2H4 system resulted in 3C-SiC(111) epilayers under all conditions of reactant gas flow and temperatures. Films of 6H-SiC(0001) were deposited on vicinal 6H-SiC(0001) substrates using the SiH4C2H4H2 system at deposition temperatures ⩾ 1350°C. In situ doping was achieved by intentional introduction of nitrogen and aluminum into the growing crystal. Monocrystalline AlN was deposited using evaporated Al and ECR plasma derived N or NH3. Films <50 Å grown on the vicinal substrates had higher defect densities compared to those on the on-axis substrates due to the higher density of inversion boundaries forming at most SiC steps in the former material. Metal/AlN/6H-SiC(0001) thin film heterostructures which had a density of trapped charges as low as of 1 × 1011 cm−2 at room temperature were prepared without post growth treatment. Superior single crystal AlNSiC heterostructures were achieved when very thin AlN was deposited on the on-axis substrates. Single phase monocrystalline solid solutions of (AlN)x(SiC)1−x were deposited between 0.2 ≤ x ≤ 0.8. A transition from the zincblende to the wurtzite structure was observed at x ≈ 0.25.}, number={10}, journal={DIAMOND AND RELATED MATERIALS}, author={Kern, RS and Jarrendahl, K and Tanaka, S and Davis, RF}, year={1997}, month={Aug}, pages={1282–1288} }
 @article{davis_weeks_bremser_tanaka_kern_sitar_ailey_perry_wang_1997, title={Growth of AlN and GaN thin films via OMVPE and gas source MBE and their characterization}, volume={41}, ISSN={["1879-2405"]}, DOI={10.1016/S0038-1101(96)00152-9}, abstractNote={Thin films of AlN and GaN are deposited primarily via the common forms of organometallic vapor phase epitaxy (OMVPE) and molecular beam epitaxy (MBE). Sapphire is the most common substrate; however, a host of materials have been used with varying degrees of success. Both growth techniques have been employed by the authors to grow AlN and GaN primarily on 6H-SiC(0001). The mismatch in atomic layer stacking sequences along the growth direction produces inversion domain boundaries in the AlN at the SiC steps; this sequence problem may discourage the nucleation of GaN. Films of AlN and GaN grown by MBE at 650°C are textured; monocrystalline films are achieved at 1050°C by this technique and OMVPE. Donor and acceptor doping of GaN has been achieved via MBE without post growth annealing. Acceptor doping in CVD material requires annealing to displace the H from the Mg and eventually remove it from the material. High brightness light emitting diodes are commercially available; however, numerous concerns regarding metal and nitrogen sources, heteroepitaxial nucleation, the role of buffer layers, surface migration rates as a function of temperature, substantial defect densities and their effect on film and device properties, ohmic and rectifying contacts, wet and dry etching and suitable gate and field insulators must and are being addressed.}, number={2}, journal={SOLID-STATE ELECTRONICS}, author={Davis, RF and Weeks, TW and Bremser, MD and Tanaka, S and Kern, RS and Sitar, Z and Ailey, KS and Perry, WG and Wang, C}, year={1997}, month={Feb}, pages={129–134} }
 @article{davis_bremser_perry_ailey_1997, title={Growth of AlN, GaN and AlxGa1-xN thin films on vicinal and on-axis 6H-SiC(0001) substrates}, volume={17}, ISSN={["0955-2219"]}, DOI={10.1016/S0955-2219(97)00077-0}, abstractNote={Monocrystalline GaN(0001) thin films were grown at 950 °Con AlN(0001) buffer layers previously deposited at 1100 °C on α(6H)-SiC(0001)si substrates via metallorganic chemical vapor deposition (MOCVD). Films of AlxGa1 − xN (0 ≤ x ≤ 1) were grown directly on the same SiC surface at 1100 °C. X-ray rocking curves for the GaN(0004) reflection for 1.4 μm films revealed FWHM values of 58 and 151 arc sec for materials grown on on-axis and offaxis substrates, respectively. Cathodoluminescence exhibited strong near band-edge emission for all materials. Controlled n- type Si-doping in GaN and AlxGa1 − xN (for x ≤ 0.4) was achieved with net carrier concentrations ranging from approximately 2 × 1017 cm− 3 to 2 × 1019 (AlxGa1 − xN) or to 1 × 1020 (GaN) cm− 3. Mg-doped, p-type GaN and AlxGa1 − xN (for x ≤ 0.13) was achieved with nA − nD ≈ 3 × 1017 cm− 3.}, number={15-16}, journal={JOURNAL OF THE EUROPEAN CERAMIC SOCIETY}, author={Davis, RF and Bremser, MD and Perry, WG and Ailey, KS}, year={1997}, pages={1775–1779} }
 @article{nam_bremser_ward_nemanich_davis_1997, title={Growth of GaN and Al0.2Ga0.8N on patterened substrates via organometallic vapor phase epitaxy}, volume={36}, ISSN={["0021-4922"]}, DOI={10.1143/JJAP.36.L532}, abstractNote={ 
   The selective growth of GaN and  Al0.2Ga0.8N has been achieved on stripe and circular patterned    GaN/AlN/6H-SiC(0001) multilayer substrates. Growth morphologies on the stripe patterns were a    function of the widths of the stripes and the flow rate of triethylgallium. No ridge growth was    observed along the top edges of the truncated stripe patterns. Smooth (0001) top facets formed on    stripes ≥5 µ m wide. Uniform hexagonal pyramid arrays of undoped GaN and Si-doped GaN    were successfully grown on 5 µ m circular patterns. Field emission measurements of a Si-doped    GaN hexagonal pyramid array exhibited a turn-on field of 25  V/µ m for an emission current of 10.8 nA at an anode-to-sample distance of 27 µ m. 
   }, number={5A}, journal={JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS}, author={Nam, OH and Bremser, MD and Ward, BL and Nemanich, RJ and Davis, RF}, year={1997}, month={May}, pages={L532–L535} }
 @article{bremser_perry_zheleva_edwards_nam_parikh_aspnes_davis_1997, title={Growth, doping and characterization of AlxGa1-xN thin film alloys on 6H-SiC(0001) substrates}, volume={6}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(96)00626-7}, abstractNote={Thin films of AlxGa1 − xN (0.05≤x≤0.96) having smooth surfaces were deposited directly on both vicinal and on-axis 6H-SiC(0001) substrates. Cross-sectional transmission electron microscopy of Al0.13Ga0.87N revealed stacking faults near the SiC/nitride alloy interface and numerous threading dislocations. Energy dispersive analysis, Auger electron spectroscopy (AES) and Rutherford backscattering were used to determine the compositions. These were paired with their respective cathodoluminescence (CL) near band-edge emission energies. A negative bowing parameter was determined. The CL emission energies were similar to the bandgap energies obtained by spectroscopic ellipsometry. Field emission AES of the initial growth of Al0.2Ga0.8N revealed an Al-rich layer near the interface. N-type (Si) doping was achieved for AlxGa1 − xN for 0.12≤x≤0.42.}, number={2-4}, journal={DIAMOND AND RELATED MATERIALS}, author={Bremser, MD and Perry, WG and Zheleva, T and Edwards, NV and Nam, OH and Parikh, N and Aspnes, DE and Davis, RF}, year={1997}, month={Mar}, pages={196–201} }
 @article{smith_wolden_bremser_hanser_davis_lampert_1997, title={High rate and selective etching of GaN, AlGaN, and AlN using an inductively coupled plasma}, volume={71}, ISSN={["0003-6951"]}, DOI={10.1063/1.120463}, abstractNote={The etching behavior of gallium nitride (GaN), aluminum gallium nitride (AlxGa1−xN), and aluminum nitride (AlN) has been systematically examined in an inductively coupled plasma (ICP) using Cl2 and Ar as the reagents. Etch rates were strongly influenced by ICP power and dc bias, while relatively insensitive to pressure, flow rate, and gas composition. Maximum etch rates of 9800 Å/min for GaN, 9060 Å/min for Al0.28Ga0.72N, and 7490 Å/min for AlN were attained. The etch profiles were highly anisotropic over the range of conditions studied. The dc bias had to exceed certain voltages before significant etch rates were obtained. These values were <−20 V for GaN, −40 V for Al0.28Ga0.72N, and >−50 V for AlN. As such, increasing selectivity for GaN over Al0.28Ga0.72N and AlN was achieved at dc biases below −40 V. At −20 V, the GaN etch rates were 38 times greater than AlN and a factor of 10 greater than Al0.28Ga0.72N. These results demonstrate the importance of ion bombardment in the etching of these materials.}, number={25}, journal={APPLIED PHYSICS LETTERS}, author={Smith, SA and Wolden, CA and Bremser, MD and Hanser, AD and Davis, RF and Lampert, WV}, year={1997}, month={Dec}, pages={3631–3633} }
 @article{kern_jarrendahl_tanaka_davis_1997, title={Homoepitaxial SiC growth by molecular beam epitaxy}, volume={202}, number={1}, journal={Physica Status Solidi. B, Basic Solid State Physics}, author={Kern, R. S. and Jarrendahl, K. and Tanaka, S. and Davis, R. F.}, year={1997}, pages={379–404} }
 @article{zavada_wilson_ren_pearton_davis_1997, title={Hydrogen incorporation and its temperature stability in SiC crystals}, volume={41}, ISSN={["0038-1101"]}, DOI={10.1016/S0038-1101(96)00249-3}, abstractNote={SiC is an important wide bandgap semiconductor material with use in high temperature electronics and as a substrate for III–V nitride epitaxial growth. In several processing stages that are required for such applications, atomic hydrogen may be introduced into the SiC material. Since atomic hydrogen is able to passivate shallow donors or acceptors, device performance may be affected. Here we report on the incorporation of hydrogen and its thermal stability in 6HSiC crystals. Hydrogen was introduced either through ion implantation or by plasma treatment. Implantation of 2H was performed at an energy of 100 keV to a fluence of 2 × 1015cm−2. In the as-implanted sample, a classical implant profile with a 2H density of about 1020 cm−3 at a depth of about 0.75 μm was obtained using secondary ion mass spectrometry (SIMS). Other samples were exposed to a 2H plasma for 30 min at 300°C. While the SIMS profiles of the plasma treated samples had a 2H peak density at the surface of about 1020 cm−3, the background level of 2H was reached in less than 0.1 μm. Samples were furnace annealed under flowing N at temperatures up to 1000°C. In contrast with Si and III–V materials, there was no significant redistribution of 2H in the implanted SiC crystal with annealing. For plasma treated samples, annealing led to a significant reduction of 2H.}, number={5}, journal={SOLID-STATE ELECTRONICS}, author={Zavada, JM and Wilson, RG and Ren, F and Pearton, SJ and Davis, RF}, year={1997}, month={May}, pages={677–679} }
 @article{wolden_davis_sitar_prater_1997, title={In situ mass spectrometry during diamond chemical vapor deposition using a low pressure flat flame}, volume={12}, ISSN={["0884-2914"]}, DOI={10.1557/JMR.1997.0364}, abstractNote={A combination of experiments and detailed kinetic modeling was used to investigate diamond deposition chemistry in low pressure combustion synthesis. Microprobe sampling was employed to provide in situ, quantitative measurements of the stable gas-phase species impinging the growth surface. The reactant gas ratio was found to be the most critical experimental variable. A detailed kinetic model was developed for the stagnation flow system. Comparison of experimental measurements showed very good agreement with model predictions. The model was then used to predict the concentration of radical species and analyze the sensitivity of predictions to γH, the probability of atomic hydrogen recombination on the surface. It was shown that γH dramatically affects the distribution of radical species near the diamond surface. The analysis also indicates that atomic carbon may be an important gas-phase precursor in this system. Comparison of mole fraction measurements and observations of film morphology were used to draw conclusions on the growth mechanism.}, number={10}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Wolden, CA and Davis, RF and Sitar, Z and Prater, JT}, year={1997}, month={Oct}, pages={2733–2742} }
 @inproceedings{rossow_edwards_bremser_kern_liu_davis_aspnes_1997, title={In-plane optical anisotropies of Al(x)Ga(1-x)N films in their regions of transparency}, DOI={10.1557/proc-449-835}, abstractNote={ABSTRACT}, booktitle={III-V nitrides: symposium held December 2-6, 1996, Boston, Massachusetts, U.S.A.  (Materials Research Society symposia proceedings ; v. 449)}, publisher={Pittsburgh, Pa.: Materials Research Society}, author={Rossow, U. and Edwards, N. V. and Bremser, M. D.. and Kern, R. S. and Liu, H. and Davis, R. F. and Aspnes, D. E.}, year={1997}, pages={835–840} }
 @article{tanikella_gruss_davis_scattergood_1997, title={Indentation and microcutting fracture damage in a silicon carbide coating on an incoloy substrate}, volume={88}, DOI={10.1016/S0257-8972(96)02910-6}, abstractNote={The fracture damage morphology for static indentation tests and controlled microcutting tests using a Vickers indentor was investigated for an amorphous silicon carbide coating deposited on an Incoloy substrate. Crack initiation thresholds were detected for both testing modes using an acoustic emission sensor. The fracture damage morphology for static indentation consisted of Hertzian-like cracks surrounding the indentation site with no lateral crack-chipping occurring up to the maximum indentation load of 8 N. In contrast, microcutting generates lateral cracks at the microcutting groove entrance for loads as low as 0.3 N. For loads up to 1 N, the groove damage was confined to the 5 μm thick coating and the fracture response is similar to that occurring in a monolithic brittle solid. At higher loads, extensive lateral crack chipping occurred along the microcutting grooves accompanied by coating decohesion at the root of the chip.}, number={1-3}, journal={Surface & Coatings Technology}, author={Tanikella, B. V. and Gruss, K. A. and Davis, R. F. and Scattergood, R. O.}, year={1997}, pages={119–126} }
 @article{parikh_suvkhanov_lioubtchenko_carlson_bremser_bray_davis_hunn_1997, title={Ion implantation of epitaxial GaN films: Damage, doping and activation}, volume={127}, ISSN={["0168-583X"]}, DOI={10.1016/S0168-583X(97)00076-1}, abstractNote={Monocrystalline GaN films grown on AlN buffer layers previously deposited on 6HSiC(0001) wafers and having dislocation densities on the order of 107 cm/cm3 beyond 0.5 μm from the initial growth interface have been achieved via chemical vapor deposition (CVD). The absence of low angle grain boundaries invariably extant in GaN films deposited on sapphire substrates and the relatively low dislocation densities and absence of stacking faults and twinning in the implantation regions of the films make them the best materials available for the study of implantation doping. In our initial study, 160 keV Si (n-type) and 120 keV Mg (p-type) with projected range ∼ 110 nm and fluences of 1e14, 5e14 and 1e15 cm−2 were implanted at both room temperature and 550°C. The samples were characterized by Rutherford backscattering (RBS)/channeling and photoluminescence (PL) techniques before and after implantation. RBS/channeling results of virgin and as-implanted GaN for 120 keV Mg at 550°C and 1e15 cm−2 fluence showed that even at this comparatively high dose the implantation damage is very little. However the characteristic PL signal which was present before the implantation disappeared even for the lowest dose (1e14 cm−2). These samples were annealed in a rapid thermal annealing furnace at 1000°C, and damage recovery and dopant activation were measured by PL, RBS/channeling and Cross-Sectional TEM (XTEM).}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS}, author={Parikh, N and Suvkhanov, A and Lioubtchenko, M and Carlson, E and Bremser, M and Bray, D and Davis, R and Hunn, J}, year={1997}, month={May}, pages={463–466} }
 @article{nam_bremser_zheleva_davis_1997, title={Lateral epitaxy of low defect density GaN layers via organometallic vapor phase epitaxy}, volume={71}, number={18}, journal={Applied Physics Letters}, author={Nam, O.-H. and Bremser, M. D. and Zheleva, T. S. and Davis, R. F.}, year={1997}, pages={2698–2640} }
 @article{wolden_davis_sitar_prater_1997, title={Low-temperature deposition of optically transparent diamond using a low-pressure flat flame}, volume={6}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(97)00155-6}, abstractNote={The radial uniformity and scaleable nature of flat flames make them an attractive technique for diamond deposition. Due to the high temperatures involved in combustion synthesis, typically molybdenum and silicon have been used as substrates. Here we report low-temperature diamond deposition on glass substrates. Diamond deposition was achieved on ordinary sodium silicate glass at substrate temperatures of ∼500°C; however, film delamination occurred during cooling after deposition. Vycor™ and Pyrex™ are two glasses that have thermal expansion coefficients that are similar to diamond. Continuous, optically transparent films were successfully deposited on both glasses. The diamond films have been characterized by scanning electron microscopy, Raman spectroscopy and secondary ion mass spectroscopy (SIMS). The dependence of hydrogen and sp2-bonded carbon incorporation in the films on reactant composition was quantified. These films were optically transparent and showed good adhesion as measured by a simple tape test.}, number={12}, journal={DIAMOND AND RELATED MATERIALS}, author={Wolden, CA and Davis, RF and Sitar, Z and Prater, JT}, year={1997}, month={Dec}, pages={1862–1867} }
 @article{smith_davis_kim_carpenter_huang_1997, title={Microstructure, electrical properties, and thermal stability of Au-based ohmic contacts to p-GaN}, volume={12}, ISSN={["2044-5326"]}, DOI={10.1557/JMR.1997.0300}, abstractNote={The work described in this paper is part of a systematic study of ohmic contact strategies for GaN-based semiconductors. Gold contacts exhibited ohmic behavior on p-GaN when annealed at high temperature. The specific contact resistivity (ρc) calculated from TLM measurements on Au/p-GaN contacts was 53 Ω · cm2 after annealing at 800 °C. Multilayer Au/Mg/Au/p-GaN contacts exhibited linear, ohmic current-voltage (I-V) behavior in the as-deposited condition with ρc = 214 Ω · cm2. The specific contact resistivity of the multilayer contact increased significantly after rapid thermal annealing (RTA) through 725 °C. Cross-sectional microstructural characterization of the Au/p-GaN contact system via high-resolution electron microscopy (HREM) revealed that interfacial secondary phase formation occurred during high-temperature treatments, which coincided with the improvement of contact performance. In the as-deposited multilayer Au/Mg/Au/p-GaN contact, the initial 32 nm Au layer was found to be continuous. However, Mg metal was found in direct contact with the GaN in many places in the sample after annealing at 725 °C for 15 s. The resultant increase in contact resistance is believed to be due to the barrier effect increased by the presence of the low work function Mg metal.}, number={9}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Smith, LL and Davis, RF and Kim, MJ and Carpenter, RW and Huang, Y}, year={1997}, month={Sep}, pages={2249–2254} }
 @article{kaminska_piotrowska_barcz_ilka_guziewicz_kasjaniuk_dynowska_kwiatkowski_bremser_davis_1997, title={Ohmic contacts to GaN by solid-phase regrowth}, volume={92}, ISSN={["0587-4246"]}, DOI={10.12693/APhysPolA.92.819}, number={4}, journal={ACTA PHYSICA POLONICA A}, author={Kaminska, E and Piotrowska, A and Barcz, A and Ilka, L and Guziewicz, M and Kasjaniuk, S and Dynowska, E and Kwiatkowski, S and Bremser, MD and Davis, RF}, year={1997}, month={Oct}, pages={819–823} }
 @article{shmagin_muth_lee_kolbas_balkas_sitar_davis_1997, title={Optical metastability in bulk GaN single crystals}, volume={71}, ISSN={["0003-6951"]}, DOI={10.1063/1.119577}, abstractNote={Bulk GaN single crystals were grown from cold pressed GaN powder by sublimation in flowing ammonia. Optical transmission measurements indicated that the absorption coefficient for the transparent samples is 50 cm−1 in the wavelength region from 650 to 400 nm. Optical metastability in bulk GaN crystals was studied through time dependent photoluminescence both at room and liquid–nitrogen temperatures. The observation included decreasing output intensity of the ultraviolet emission attributed to the band edge and increasing output intensity of a new emission band centered at 378 nm at room temperature. At liquid–nitrogen temperature, the photoinduced emission band consisted of at least one LO-phonon replica of the zero-phonon line centered at 378 nm. The ratio of output intensities of the photoinduced band to the band edge increased by a factor of 10 during 27 min of exposure time. The photoinduced effect is attributed to the metastable nature of traps in bulk GaN.}, number={4}, journal={APPLIED PHYSICS LETTERS}, author={Shmagin, IK and Muth, JF and Lee, JH and Kolbas, RM and Balkas, CM and Sitar, Z and Davis, RF}, year={1997}, month={Jul}, pages={455–457} }
 @article{bergman_bremser_perry_davis_dutta_nemanich_1997, title={Raman analysis of the configurational disorder in AlxGa1-xN films}, volume={71}, ISSN={["0003-6951"]}, DOI={10.1063/1.119367}, abstractNote={Raman analysis of the E2 mode of AlxGa1−xN in the composition range 0⩽x⩽1 is presented. The line shape was observed to exhibit a significant asymmetry and broadening toward the high energy range. The spatial correlation model is discussed, and is shown to account for the line shape. The model calculations also indicate the lack of a long-range order in the chemical vapor deposition alloys. These results were confirmed by x-ray scattering: the relative intensity of the superlattice line was found to be negligible. The line broadening of the E2 mode was found to exhibit a maximum at a composition x≅0.5 indicative of a random disordered alloy system.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Bergman, L and Bremser, MD and Perry, WG and Davis, RF and Dutta, M and Nemanich, RJ}, year={1997}, month={Oct}, pages={2157–2159} }
 @article{kern_davis_1997, title={Silicon carbide for high-temperature microelectronics: recent advances in material growth via gas source MBE and device research}, volume={46}, number={1-3}, journal={Materials Science & Engineering. B, Solid-state Materials for Advanced Technology}, author={Kern, R. S. and Davis, R. F.}, year={1997}, pages={240–247} }
 @article{edwards_yoo_bremser_zheleva_horton_perkins_weeks_liu_stall_kuech_et al._1997, title={Spectral analysis of above-, below-, and near-bandedge phenomena in GaN thin films}, volume={50}, ISSN={["0921-5107"]}, DOI={10.1016/s0921-5107(97)00151-7}, abstractNote={We report spectroscopic ellipsometry (SE) and low-temperature reflectance data on epitaxial GaN thin film samples covering the widest range of tensile and compressive stress (−3.8–3.5 kbar) thus far. SE allows us to assess the preparation of smooth and abrupt GaN surfaces by chemical treatments in real time, and, coupled with the reflectance data, the E dn/dE contribution to dispersion, which is important for laser action. The reflectance data explicitly show the nonlinear behavior of the B–A and C–A splittings versus the energy of the A exciton. Lineshape ambiguities that hindered previous interpretations have been resolved with reciprocal space analysis, allowing us to obtain band parameters such as ΔSO=17.0±1 meV and ΔCF=9.8±1 meV with increased confidence.}, number={1-3}, journal={MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, author={Edwards, NV and Yoo, SD and Bremser, MD and Zheleva, T and Horton, MN and Perkins, NR and Weeks, TW and Liu, H and Stall, RA and Kuech, TF and et al.}, year={1997}, month={Dec}, pages={134–141} }
 @article{balkas_sitar_zheleva_bergman_nemanich_davis_1997, title={Sublimation growth and characterization of bulk aluminum nitride single crystals}, volume={179}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(97)00160-7}, abstractNote={Single crystalline platelets of aluminum nitride (AlN) ⩽ 1 mm thick have been grown within the temperature range of 1950–2250°C on 10 × 10 mm2 α(6H)-silicon carbide (SiC) substrates via sublimation-recondensation in a resistively heated graphite furnace. The source material was sintered AlN. A maximum growth rate of 500 μm/h was achieved at 2150°C and a source-to-seed separation of 4 mm. Growth rates below 2000°C were approximately one order of magnitude lower. Crystals grown at high temperatures ranged in color from blue to green due to the incorporation of Si and C from the SiC substrates; those grown at lower temperatures were colorless and transparent. Secondary-ion mass spectroscopy (SIMS) results showed almost a two order of magnitude decrease in the concentrations of these two impurities in the transparent crystals. Plan view transmission electron microscopy (TEM) of these crystals showed no line or planar defects. Raman spectroscopy and X-ray diffraction (XRD) studies indicated a strain free material.}, number={3-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Balkas, CM and Sitar, Z and Zheleva, T and Bergman, L and Nemanich, R and Davis, RF}, year={1997}, month={Aug}, pages={363–370} }
 @article{hiramatsu_kawaguchi_shimizu_sawaki_zheleva_davis_tsuda_taki_kuwano_oki_1997, title={The composition pulling effect in MOVPE grown InGaN on GaN and AlGaN and its TEM characterization}, volume={2}, number={6}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Hiramatsu, K. and Kawaguchi, Y. and Shimizu, M. and Sawaki, N. and Zheleva, T. S. and Davis, R. F. and Tsuda, H. and Taki, W. and Kuwano, N. and Oki, K.}, year={1997} }
 @article{sowers_christman_bremser_ward_davis_nemanich_1997, title={Thin films of aluminum nitride and aluminum gallium nitride for cold cathode applications}, volume={71}, DOI={10.1063/1.120052}, abstractNote={Cold cathode structures have been fabricated using AlN and graded AlGaN structures (deposited on n-type 6H-SiC) as the thin film emitting layer. The cathodes consist of an aluminum grid layer separated from the nitride layer by a SiO2 layer and etched to form arrays of either 1, 3, or 5 μm holes through which the emitting nitride surface is exposed. After fabrication, a hydrogen plasma exposure was employed to activate the cathodes. Cathode devices with 5 μm holes displayed emission for up to 30 min before failing. Maximum emission currents ranged from 10–100 nA and required grid voltages ranging from 20–110 V. The grid currents were typically 1 to 104 times the collector currents.}, number={16}, journal={Applied Physics Letters}, author={Sowers, A. T. and Christman, J. A. and Bremser, M. D. and Ward, B. L. and Davis, R. F. and Nemanich, R. J.}, year={1997}, pages={2289–2291} }
 @article{edwards_yoo_bremser_weeks_nam_davis_liu_stall_horton_perkins_et al._1997, title={Variation of GaN valence bands with biaxial stress and quantification of residual stress}, volume={70}, ISSN={["0003-6951"]}, DOI={10.1063/1.119089}, abstractNote={Low-temperature reflectance data on epitaxial GaN thin-film samples covering the widest range of tensile and compressive stress (−3.8–3.5 kbar) thus far explicitly show the nonlinear behavior of the B–A and C–A splittings versus the energy of the A exciton. Lineshape ambiguities that hindered previous interpretations have been resolved with reciprocal-space analysis, allowing us to obtain band parameters such as ΔSO=17.0±1meV with increased confidence.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Edwards, NV and Yoo, SD and Bremser, MD and Weeks, TW and Nam, OH and Davis, RF and Liu, H and Stall, RA and Horton, MN and Perkins, NR and et al.}, year={1997}, month={Apr}, pages={2001–2003} }
 @inproceedings{edwards_yoo_bremser_horton_perkins_weeks_liu_stall_kuech_davis_et al._1997, title={Variation of GaN valence bands with biaxial stress: quantification of residual stress and impact on fundamental band parameters}, DOI={10.1557/proc-449-781}, abstractNote={ABSTRACT}, booktitle={III-V nitrides: symposium held December 2-6, 1996, Boston, Massachusetts, U.S.A.  (Materials Research Society symposia proceedings ; v. 449)}, publisher={Pittsburgh, Pa.: Materials Research Society}, author={Edwards, N. V. and Yoo, S. D. and Bremser, M. D. and Horton, M. N. and Perkins, N. R. and Weeks, T. W. and Liu, H. and Stall, R. A. and Kuech, T. F. and Davis, R. F. and et al.}, year={1997}, pages={781–786} }
 @inproceedings{balkas_sitar_zheleva_bergman_shmagin_muth_kolbas_nemanich_davis_1996, title={Growth of bulk AIN and GaN single crystals by sublimation}, booktitle={III-V nitrides: symposium held December 2-6, 1996, Boston, Massachusetts, U.S.A.  (Materials Research Society symposia proceedings ; v. 449)}, publisher={Pittsburgh, Pa.: Materials Research Society}, author={Balkas, C. M. and Sitar, Z. and Zheleva, T. and Bergman, L. and Shmagin, I. K. and Muth, J. F. and Kolbas, R. M. and Nemanich, R. and Davis, R. F.}, year={1996}, pages={41–46} }
 @article{kisielowski_kruger_ruvimov_suski_ager_jones_lilientalweber_rubin_weber_bremser_et al._1996, title={Strain-related phenomena in GaN thin films}, volume={54}, number={24}, journal={Physical Review. B, Condensed Matter and Materials Physics}, author={Kisielowski, C. and Kruger, J. and Ruvimov, S. and Suski, T. and Ager, J. W. and Jones, E. and Lilientalweber, Z. and Rubin, M. and Weber, E. R. and Bremser, M. D. and et al.}, year={1996}, pages={17745–17753} }
 @misc{davis_wang_1995, title={Germanium doped n-type aluminum nitride epitaxial layers}, volume={7,682,709}, number={1995 Oct. 30}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Davis, R. F. and Wang, C.}, year={1995} }
 @misc{glass_palmour_davis_porter_1995, title={Method of forming platinum ohmic contact to p-type silicon carbide}, volume={5,409,859}, number={1995 Apr. 25}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Glass, R. C. and Palmour, J. W. and Davis, R. F. and Porter, L. S.}, year={1995} }
 @misc{davis_carter_hunter_1995, title={Sublimation of silicon carbide to produce large, device quality single crystals of silicon carbide}, volume={RE34,861}, number={1995 Feb. 14}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Davis, R. F. and Carter, C. H. and Hunter, C. E.}, year={1995} }
 @misc{glass_palmour_davis_porter_1994, title={Platinum ohmic contact to p-type silicon carbide}, volume={5,323,022}, number={1994 Jun. 21}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Glass, R. C. and Palmour, J. W. and Davis, R. F. and Porter, L. S.}, year={1994} }
 @book{robert f. davis_1993, title={Diamond films and coatings development, properties, and applications}, publisher={Park Ridge, NJ: Noyes Pub.}, author={Robert F. Davis}, year={1993} }
 @misc{edmond_davis_1992, title={Implantation and electrical activation of dopants into monocrystalline silicon carbide}, volume={5,087,576}, number={1992 Feb. 11}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Edmond, J. A. and Davis, R. F.}, year={1992} }
 @misc{kong_glass_davis_1991, title={Homoepitaxial growth of Alpha-SiC thin films and semiconductor devices fabricated thereon}, volume={5,011,549}, number={1991 Apr. 30}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Kong, H. S. and Glass, J. T. and Davis, R. F.}, year={1991} }
 @article{davis_1991, title={III-V NITRIDES FOR ELECTRONIC AND OPTOELECTRONIC APPLICATIONS}, volume={79}, ISSN={["0018-9219"]}, DOI={10.1109/5.90133}, abstractNote={Recent developments in III-V nitride thin-film materials for electronic and optoelectronic applications are reviewed. The problems that are limiting the development of these materials and devices made from them are discussed. The properties of cubic boron nitride, aluminum nitride, gallium nitride, AlN/GaN solid solutions and heterostructures, and indium nitride are discussed. It is pointed out that the lack of a suitable substrate, with the possible exception of SiC for AlN, is a problem of considerable magnitude. This is compounded by the presence of shallow donor bands in GaN and InN which are apparently caused by N vacancies. The question of whether these vacancies occur (if they do) as a result of intrinsic or extrinsic (as a result of deposition) nonstoichiometry has not been answered. However, the recent advances in the fabrication of p-type GaN and a p-n junction light emitting diode via the electron beam stimulation of the Mg dopant are very encouraging and may considerably advance the technology of this material. This would indicate that self-compensation effects, similar to those observed in ZnO and ZnSe, may not be present in the III-V nitrides, since cubic BN (cBN) AlN and now GaN have been reportedly doped both n- and p-type. >}, number={5}, journal={PROCEEDINGS OF THE IEEE}, author={DAVIS, RF}, year={1991}, month={May}, pages={702–712} }
 @article{davis_kelner_shur_palmour_edmond_1991, title={THIN-FILM DEPOSITION AND MICROELECTRONIC AND OPTOELECTRONIC DEVICE FABRICATION AND CHARACTERIZATION IN MONOCRYSTALLINE ALPHA AND BETA SILICON-CARBIDE}, volume={79}, ISSN={["1558-2256"]}, DOI={10.1109/5.90132}, abstractNote={The deposition of silicon carbide thin films and the associated technologies of impurity incorporation, etching, surface chemistry, and electrical contacts for fabrication of solid-state devices capable of operation at temperatures to 925 K are addressed. The results of several research programs in the United States, Japan and the Soviet Union, and the remaining challenges related to the development of silicon carbide for microelectronics are presented and discussed. It is concluded that the combination of alpha -SiC on alpha -SiC appears especially viable for device fabrication. In addition, considerable progress in the understanding of the surface science, ohmic and Schottky contacts, and dry etching have recently been made. The combination of these advances has allowed continual improvement in Schottky diode p-n junction, MESFET, MOSFET, HBT, and LED devices. >}, number={5}, journal={PROCEEDINGS OF THE IEEE}, author={DAVIS, RF and KELNER, G and SHUR, M and PALMOUR, JW and EDMOND, JA}, year={1991}, month={May}, pages={677–701} }
 @misc{davis_kong_glass_carter_1990, title={Growth of beta-sic thin films and semiconductor devices fabricated thereon}, volume={4,912,063}, number={1990 Mar. 27}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Davis, R. F. and Kong, H. S. and Glass, J. T. and Carter, C. H.}, year={1990} }
 @misc{kong_glass_davis_1990, title={Homoepitaxial growth of alpha-SiC thin films and semiconductor devices fabricated thereon}, volume={4,912,064}, number={1990 Mar. 27}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Kong, H. S. and Glass, J. T. and Davis, R. F.}, year={1990} }
 @misc{edmond_davis_1990, title={P-N junction diodes in silicon carbide}, volume={4,947,218}, number={1990 Aug. 7}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Edmond, J. A. and Davis, R. F.}, year={1990} }
 @article{paisley_sitar_posthill_davis_1989, title={GROWTH OF CUBIC PHASE GALLIUM NITRIDE BY MODIFIED MOLECULAR-BEAM EPITAXY}, volume={7}, ISSN={["0734-2101"]}, DOI={10.1116/1.575869}, abstractNote={Gallium nitride is a compound semiconductor with a wide direct band gap (3.45 eV) and a large saturated electron drift velocity. Nearly all single-crystal thin films grown to date have been wurtzite (hexagonal) structure. Cubic GaN has the potential for higher saturated electron drift velocity and somewhat lower band gap. These properties could increase its applicability for high-frequency devices (such as impact ionization avalanche transit time diodes) as well as short-wavelength light emitting diodes and semiconductor lasers. This paper reports the growth of cubic phase single-crystal thin-film GaN using a modified molecular-beam epitaxy technique. A standard effusion cell was used for gallium, but to activate nitrogen gas prior to deposition, a microwave glow discharge was used. Auger electron spectroscopy showed a nominally stoichiometric GaN film. Transmission electron microscopy with selected area diffraction indicated the crystal structure to be zinc blende.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS}, author={PAISLEY, MJ and SITAR, Z and POSTHILL, JB and DAVIS, RF}, year={1989}, pages={701–705} }
 @misc{davis_carter_hunter_1989, title={Sublimation of silicon carbide to produce large, device quality single crystals of silicon carbide}, volume={4,866,005}, number={1989 Sep. 12}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Davis, R. F. and Carter, C. H. and Hunter, C. E.}, year={1989} }