@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{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{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{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{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{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{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} }