@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} }
 @article{shin_nam_jun_park_1999, title={Biological uptake of influent organic matter as an electron donor for denitrification by activated sludge}, volume={13}, ISSN={["0951-208X"]}, DOI={10.1023/A:1008998113204}, number={6}, journal={BIOTECHNOLOGY TECHNIQUES}, author={Shin, HS and Nam, SY and Jun, HB and Park, HS}, year={1999}, month={Jun}, pages={415–418} }
 @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} }