@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{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{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{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{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} }
 @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{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{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{kasic_schubert_einfeldt_hommel_2002, title={Infrared spectroscopic ellipsometry - a new tool for characterization of semiconductor heterostructures}, volume={29}, ISSN={["0924-2031"]}, DOI={10.1016/S0924-2031(01)00197-7}, abstractNote={Spectroscopic ellipsometry (SE) for infrared wavelengths is presented as a novel technique for contactless and nondestructive measurement of free-carrier and crystal-structure properties of complex semiconductor heterostructures for device applications. Infrared (IR)-active lattice vibrations and LO phonon–plasmon coupled modes dominate the infrared dielectric response of semiconductor materials. Analysis of ellipsometry data from 2 to 33 μm can precisely determine thin-film dielectric functions (DF) without numerical Kramers–Kronig analysis and thus provides information on phonon mode frequencies and broadening parameters, static dielectric constants, and free-carrier parameters, even for films with thicknesses only a fraction of the probing wavelengths. Alloy composition, film strain, and crystal quality of sample constituents in thin-film heterostructures can be derived. An infrared dielectric function database, which was established by analysis of simple heterostructures, is used for the investigation of complex device structures. As an example, we demonstrate the characterization of a laser diode (LD) structure based on group-III-nitride materials, where information such as concentration and mobility of free carriers in the n- and p-type regions, thickness, alloy composition, and quality of device constituents are accessible.}, number={1-2}, journal={VIBRATIONAL SPECTROSCOPY}, author={Kasic, A and Schubert, M and Einfeldt, S and Hommel, D}, year={2002}, month={Jul}, pages={121–124} }
 @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} }
 @article{kasic_schubert_off_scholz_einfeldt_hommel_2002, title={Optical phonons in hexagonal AlxInyGa1-x-yN (y approximate to 0.12)}, volume={234}, number={3}, journal={Physica Status Solidi. B, Basic Solid State Physics}, author={Kasic, A. and Schubert, M. and Off, J. and Scholz, F. and Einfeldt, S. and Hommel, D.}, year={2002}, pages={970–974} }
 @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{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} }