@article{dutta_alexson_bergman_nemanich_dupuis_kim_komirenko_stroscio_2001, title={Phonons in III–V nitrides: Confined phonons and interface phonons}, volume={11}, ISSN={1386-9477}, url={http://dx.doi.org/10.1016/S1386-9477(01)00217-X}, DOI={10.1016/S1386-9477(01)00217-X}, abstractNote={Phonons in III–V nitrides are examined experimentally for dimensionally confined systems and for alloys of InGaN with a view towards understanding the phonon modes of these systems. Results are compared with the predictions of Loudon's model for uniaxial semiconductors. The modes of the InGaN system are compared with those of the AlGaN ternary alloy. The first Raman measurements of interface phonons in binary GaN–AlN superlattices are presented.}, number={2-3}, journal={Physica E: Low-dimensional Systems and Nanostructures}, publisher={Elsevier BV}, author={Dutta, M and Alexson, D and Bergman, L and Nemanich, R.J and Dupuis, R and Kim, K.W and Komirenko, S and Stroscio, M}, year={2001}, month={Oct}, pages={277–280} }
 @article{gracin_borjanovic_vlahovic_sunda-meya_patterson_dutta_hauger_pinayev_ware_alexson_et al._2001, title={Selective bond breaking in amorphous hydrogenated silicon by using Duke FEL}, volume={475}, ISSN={["0168-9002"]}, DOI={10.1016/S0168-9002(01)01578-9}, abstractNote={In order to study the possibility of influencing the phase containing predominantly Si–H bonds, while having minimal influence on the surrounding materials, samples of a-Si were exposed to Duke-FEL Mark III radiation. The wavelength of the radiation was selected to fit the absorption maximum of stretching vibrations of Si–H bonds (5 μm). By varying the wavelength in the vicinity of 5 μm, the illumination time and the power density, different types and degrees of structural ordering, of Si–H bonds and Si–Si bonds were obtained, and monitored by Raman spectroscopy. By increasing the energy density, at certain level the crystallization occurs. We were able to demonstrate a direct correlation between short and intermediate range ordering and the wavelength and intensity of the radiation. Using 5 μm at 10 kW/cm2 leads to increase in structural disordering. However, increasing power to 60 kW/cm2 improves both short and intermediate order in a-Si : H, as demonstrated by Raman spectroscopy. Further increasing power density by an order of magnitude results in crystallization of the sample.}, number={1-3}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT}, author={Gracin, D and Borjanovic, V and Vlahovic, B and Sunda-Meya, A and Patterson, TM and Dutta, JM and Hauger, S and Pinayev, I and Ware, ME and Alexson, D and et al.}, year={2001}, month={Dec}, pages={635–639} }
 @article{alexson_bergman_nemanich_dutta_stroscio_parker_bedair_el-masry_adar_2001, title={Ultraviolet raman study of A(1)(LO) and E-2 phonons in InxGa1-xN alloys}, volume={89}, ISSN={["0021-8979"]}, DOI={10.1063/1.1330760}, abstractNote={We report on ultraviolet Raman spectroscopy of InxGa1−xN thin films grown on sapphire by metal-organic chemical vapor deposition. The A1(LO) and E2 phonon mode behavior was investigated over a large compositional range (0<x<0.50). Compelling evidence is presented for one-mode behavior for the A1(LO) phonon, and data suggestive of two-mode behavior are presented for the E2 phonon.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Alexson, D and Bergman, L and Nemanich, RJ and Dutta, M and Stroscio, MA and Parker, CA and Bedair, SM and El-Masry, NA and Adar, F}, year={2001}, month={Jan}, pages={798–800} }
 @article{alexson_bergman_dutta_kim_komirenko_nemanich_lee_stroscio_yu_1999, title={Confined phonons and phonon-mode properties of III–V nitrides with wurtzite crystal structure}, volume={263-264}, ISSN={0921-4526}, url={http://dx.doi.org/10.1016/S0921-4526(98)01423-9}, DOI={10.1016/s0921-4526(98)01423-9}, abstractNote={Stimulated by the recent interest in the use of nitride-based III–V wurtzite structures for optoelectronic and electronic devices, this paper reports on the application of the Loudon model for uniaxial crystals to derive the Fröhlich interaction Hamiltonian as well as the electron–optical-phonon scattering rate in wurtzite crystals. This paper also presents experimental analyses of the mode behavior of phonons in wurtzite crystals.}, journal={Physica B: Condensed Matter}, publisher={Elsevier BV}, author={Alexson, D and Bergman, Leah and Dutta, Mitra and Kim, K.W and Komirenko, S and Nemanich, Robert J and Lee, B.C and Stroscio, Michael A and Yu, SeGi}, year={1999}, month={Mar}, pages={510–513} }
 @article{bergman_alexson_nemanich_dutta_stroscio_balkas_davis_1999, title={Phonon dynamics and lifetimes of AlN and GaN crystallites}, volume={4S1}, DOI={10.1557/s1092578300003422}, abstractNote={The quasi-LO and quasi-TO modes of AlN crystallite were investigated. The analysis indicates that the Raman mode behavior concurs with Loudons’ model of mode-mixing in wurtzite (WZ) structure crystals which is due to the long-range electrostatic field. Phononlifetimes of GaN and AlN crystallites were studied via Raman lineshape. It was found that the low energy E2 mode lifetime is about an order of magnitude longer than that of the other modes, and that impurities impact significantly the phonon-lifetimes.}, number={G6.65}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Bergman, L. and Alexson, D. and Nemanich, R. J. and Dutta, M. and Stroscio, M. A. and Balkas, C. and Davis, R. F.}, year={1999} }
 @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} }
 @article{bergman_dutta_balkas_davis_christman_alexson_nemanich_1999, title={Raman analysis of the E1 and A1 quasi-longitudinal optical and quasi-transverse optical modes in wurtzite AlN}, volume={85}, ISSN={["0021-8979"]}, DOI={10.1063/1.369712}, abstractNote={This article presents a study of the quasi-longitudinal optical and quasi-transverse optical modes in wurtzite AlN which originate from the interaction of phonons belonging to the A1 and E1 symmetry groups. In order to analyze the allowed quasi as well as pure Raman modes, the modes were observed in a rotating crystallographic coordinate system, and the Raman tensors of the wurtzite crystal structure were calculated as a function of the crystallographic rotation. The frequencies of the quasimodes of wurtzite AlN were also analyzed in terms of the interaction of the polar phonons with the long range electrostatic field model. The experimental values of the Raman frequencies of the quasiphonons concur with these expected from the model, implying that the long range electrostatic field dominates the short range forces for polar phonons in AlN.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Bergman, L and Dutta, M and Balkas, C and Davis, RF and Christman, JA and Alexson, D and Nemanich, RJ}, year={1999}, month={Apr}, pages={3535–3539} }