@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{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{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} }
 @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{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{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{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} }
 @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} }
 @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{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} }
 @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{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} }
 @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{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} }