@article{choi_aspnes_stoute_kim_kim_chang_palmstrom_2008, title={Dielectric properties of InAsP alloy thin films and evaluation of direct- and reciprocal-space methods of determining critical-point parameters}, volume={205}, ISSN={["1862-6300"]}, DOI={10.1002/pssa.200777848}, abstractNote={Abstract Spectroscopic ellipsometry is used to determine pseudodielectric function spectra 〈 ε 〉 = 〈 ε 1 〈 + i 〈 ε 2 〈 of InAs x P 1– x al‐loy thin films from 1.5 to 6.0 eV at room temperature. The structures for the E 1 , E 1 + Δ 1 , E ′ 0 , E 2 , and E ′ 2 critical points (CPs) were observed in the data. We compare direct‐ and reciprocal‐space methods of extracting CP energies E g . The direct‐space values show less uncertainty, a result of how the two procedures use available information. Energies obtained are compared with the results of theoretical calculations using the linear augmented Slater‐type orbital (LASTO) method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={4}, journal={PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE}, author={Choi, S. G. and Aspnes, D. E. and Stoute, N. A. and Kim, Y. D. and Kim, H. J. and Chang, Y. -C. and Palmstrom, C. J.}, year={2008}, month={Apr}, pages={884–887} }
 @article{chang_cai_muth_kolbas_park_cuomo_hanser_bumgarner_2003, title={Optical and structural studies of hydride vapor phase epitaxy grown GaN}, volume={21}, ISSN={["0734-2101"]}, DOI={10.1116/1.1568346}, abstractNote={Thick films of hydride vapor phase epitaxy (HVPE) grown GaN were studied by various techniques. Time-integrated and time-resolved photoluminescence (PL) measurements were performed at room temperature and 77 K. The time-integrated PL spectrum has no observed deep-level transitions and a very narrow linewidth, which indicates good material quality. Time-resolved PL spectra are also presented and the temporal evolution of the PL around the band-gap exhibits a biexponential decay with a fast and a slow decay component. Cathodoluminescence, x-ray, and Raman spectroscopy were also used. The full width half maximum of the x-ray rocking curve for our sample is approximately 375 arcsec. The polarized Raman spectra exhibited only the allowed modes. The deposited GaN films were found to be relatively stress free. The x ray and Raman analysis also revealed that the HVPE-grown GaN films are of high crystal quality. The effect of thermal annealing on the sample was also investigated by time-integrated and time-resolved PL and Raman spectroscopy. No significant changes in the material were observed in either time-integrated or Raman spectroscopy. The film was thermally stable upon annealing up to 1000 °C in N2 ambient based on the results of these measurements. In time-resolve photoluminescence measurement, the temporal evolution of the band-edge transitions broadens after each annealing step and is significantly different after the 1000 °C anneal.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Chang, YC and Cai, AL and Muth, JF and Kolbas, RM and Park, M and Cuomo, JJ and Hanser, A and Bumgarner, J}, year={2003}, pages={701–705} }
 @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{park_maria_cuomo_chang_muth_kolbas_nemanich_carlson_bumgarner_2002, title={X-ray and Raman analyses of GaN produced by ultrahigh-rate magnetron sputter epitaxy}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1506781}, abstractNote={Thick films of GaN were studied by x-ray diffraction and Raman spectroscopy. The GaN thick films were deposited on (0001) sapphire using ultrahigh-rate magnetron sputter epitaxy with typical growth rates as high as 10–60 μm/min. The width of the x-ray rocking curve from the (0002) reflection for the sample produced by this technique is ∼300 arcsec, which is unprecedented for GaN produced by a sputtering-type process. Our recent sample shows an x-ray rocking curve width of 240 arcsec. Only allowed modes were observed in the polarized Raman spectra. The background free carrier concentration is lower than 3×1016 cm−3. The phonon lifetime of the Raman E2(2) mode of the sputtered GaN was comparable to that of bulk single crystal GaN grown by sublimation. The quality of the film was uniform across the wafer. The film was thermally stable upon annealing in N2 ambient. The x-ray and Raman analyses revealed that the sputtered GaN films are of high crystalline quality.}, number={10}, journal={APPLIED PHYSICS LETTERS}, author={Park, M and Maria, JP and Cuomo, JJ and Chang, YC and Muth, JF and Kolbas, RM and Nemanich, RJ and Carlson, E and Bumgarner, J}, year={2002}, month={Sep}, pages={1797–1799} }
 @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{bergmann_ozgur_casey_muth_chang_kolbas_rao_eom_schurman_1999, title={Linear optical properties of a heavily Mg-doped Al0.09Ga0.91N epitaxial layer}, volume={74}, ISSN={["0003-6951"]}, DOI={10.1063/1.124102}, abstractNote={The room-temperature absorption coefficient and ordinary refractive index for a ∼0.4-μm-thick p-type wurtzite Al0.09Ga0.91N epitaxial layer were determined via optical transmission measurements. The layer was grown by metal organic chemical vapor deposition and heavily doped (∼5×1019 cm−3) with Mg. Additional measurements of the refractive index by prism coupling to the layer confirmed the transmission results. The low-temperature AlN buffer layer altered the expected interference fringes of the transmission spectrum below the band-gap energy and had to be accounted for in the analysis. The absorption coefficient exhibited band-tail effects and had a reduced slope near band-gap energy as compared to undoped GaN. Using a detailed balance argument, the reduced slope was consistent with the lack of a peak in the continuous-wave photoluminescent emission.}, number={21}, journal={APPLIED PHYSICS LETTERS}, author={Bergmann, MJ and Ozgur, U and Casey, HC and Muth, JF and Chang, YC and Kolbas, RM and Rao, RA and Eom, CB and Schurman, M}, year={1999}, month={May}, pages={3188–3190} }