Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session D37: Optical Properties of Semiconductors (mostly nitrides) |
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Sponsoring Units: FIAP Chair: Mark Holtz, Texas Tech University Room: Morial Convention Center 229 |
Monday, March 10, 2008 2:30PM - 2:42PM |
D37.00001: Magnetooptic Ellipsometry: Determination of free charge carrier properties in semiconductor device structures Mathias Schubert, Tino Hofmann The standard tool for the electrical characterization of free charge properties in semiconductor layer structures is the electrical Hall effect. However, besides the requirement for electrical contacts, the application of this technique to investigate complex heterostructures is very difficult and reliable deconvolution of the individual layer contributions to the measured Hall-Voltage virtually impossible. In our contribution we show that magnetooptic ellipsometry at long wavelengths when applied to conducting or semiconducting multilayer structures can yield equivalent and even much increased information. Our technique allows the independent measurement of free charge carrier density, type, mobility, and effective mass including anisotropy without any electrical contact in buried structures, and which may have been inaccessible to any true electrical evaluation thus far. We present results for multilayer AlGaP and GaInP samples with different doping concentrations. Furthermore, multilayer LED device structures were investigated and we demonstrate that magnetooptic ellipsometry allows deconvolution of the individual free charge carrier contributions of the p- and n-type regions of the device structure. We predict a realm of applications for magnetooptic ellipsometry in future materials research and engineering. [Preview Abstract] |
Monday, March 10, 2008 2:42PM - 2:54PM |
D37.00002: Cyclotron mass of two-dimensional holes in (100) oriented GaAs/AlGaAs heterostructures T.M. Lu, Z.F. Li, D.C. Tsui, M.J. Manfra, L.N. Pfeiffer, K.W. West We have measured the microwave cyclotron resonance of low-density two-dimensional hole gases in (100) oriented heterostructures, including single interface heterostructures (SIHs) and 20nm-wide quantum wells(QWs). It was found that in the case of the SIHs, the cyclotron mass is relatively insensitive to the hole density, ranging from $0.25\times10^{10}$/cm$^2$ to $13.1\times10^{10}$/cm$^2$, and has a value of approximately $0.5m_{e}$. On the other hand, for holes in the QWs, the cyclotron mass decreases from $0.48m_{e}$ at density $p=6.9\times10^{10}$/cm$^2$ to $0.29m_{e}$ at $p=0.8\times10^{10}$/cm$^2$. In this talk, the absorption spectra will be shown, and a qualitative explanation will be presented. [Preview Abstract] |
Monday, March 10, 2008 2:54PM - 3:06PM |
D37.00003: High-Gap Semiconductors and Their Absorption Mechanisms at Millimeter and Submillimeter Wavelengths J.M. Dutta, C.R. Jones, V. Parshin, B. Garin, V. Polyakov, A. Rukovishnikov Experimental data has been applied to extend the available theoretical models to elucidate the predominate mechanisms of absorption for mm and sub-mm electromagnetic waves in high-gap semiconductors, especially CVD diamond and SiC, which are among the most promising low-loss materials commercially available. Dielectric properties of CVD diamonds, as measured by several laboratories, over a wide range of temperature and frequency will be discussed. The experimental data gathered, both from dielectric and electrical measurements, has been applied to extend available theoretical models for CVD diamonds. Similar studies are undertaken on SiC to determine the primary loss mechanisms for SiC in the mm wavelength range. Preliminary experimental results will be presented. [Preview Abstract] |
Monday, March 10, 2008 3:06PM - 3:18PM |
D37.00004: Propagation of light in birefringent tilings Angelo Mascarenhas, Brian Fluegel, Lekhnath Bhusal Two-dimensional tilings of an optically birefringent material are proposed as an orientational superlattice for light. The light modes that result from loss-free refraction are analyzed. It is shown that the behavior for light propagation in such lattices leads to totally bound as well as propagating states. The behavior of light propagation in several such tilings is compared. [Preview Abstract] |
Monday, March 10, 2008 3:18PM - 3:30PM |
D37.00005: Properties of Bulk GaN Crystals grown from the Solution Madhu Murthy, Jaime A. Freitas Jr., Micheal A. Mastro, Rachel M. Frazier, Boris N. Feigelson We investigated the structural and optical properties of bulk GaN single crystal grown from solution at temperatures $<$ 900$^{\circ}$C and a pressure of $\sim $ 0.3Mpa [1] on HVPE substrates. The X-ray diffraction peaks measured on both Ga- and N-face of the epitaxial film are 34.561 and 34.612 \textit{arcsec}, respectively, which are two orders of magnitude lower than the substrate. The photoluminescence measurements performed on both faces of the sample, showed a dominant intense emission near 3.47 eV, which is assigned to recombination process involving shallow impurities and excitons [2]. Two additional bands observed at 3.25 eV and 2.25 eV are assigned to donor-acceptor recombination process and the yellow band, respectively. The relative decrease of these bands intensities suggests a reduction of the concentration of defects incorporated in the epitaxial film, as compared with the substrate. These variations are consistent with different incorporation rate of point defects at different crystal surface polarity. [1] B.N. Feigelson, et al., J. Cryst. Growth, 281 (2005) 5. [2] M. Murthy, et al., J. Cryst. Growth, 305 (2007) 393. [Preview Abstract] |
Monday, March 10, 2008 3:30PM - 3:42PM |
D37.00006: Optical properties of MOCVD selective area growth of GaN D.Y. Song, A. Chandolu, L. Tian, N. Stojanovic, S.A. Nikishin, M. Holtz Selective area growth (SAG) is useful for overcoming mismatch between non-native substrates and epitaxial materials. SAG of GaN is carried out using metallorganic chemical vapor deposition with silicon dioxide as the mask material with openings ranging from 500 nm to several microns. This talk addresses optical properties of completed GaN pyramidal islands grown using SAG. SEM-based cathodoluminescence (CL) is used to investigate the bandgap emission. The optical properties at different positions on the pyramids are related to overgrowth conditions which determine the luminescence properties. The apex region is almost fully relaxed, while the pyramid base exhibits a red-shifted CL spectrum. This shift is attributed to stress and impurity incorporation in the overgrown sidewall region. The red shift observed in CL spectra on the pyramid sidewall region gradually increases from apex to base, varying by $\sim $ 40 meV, when they exceed the size of the opening in the silicon dioxide mask. However, the pyramid has almost uniform luminescence properties when overgrowth does not occur. The CL line width is narrowest at the pyramid apex, suggesting a decrease in the dislocation density. The authors acknowledge support from the National Science Foundation (ECS--0609416 and ECS--0304224) and the J. F Maddox Foundation. [Preview Abstract] |
Monday, March 10, 2008 3:42PM - 3:54PM |
D37.00007: Insights into the Electronic Structure of Single-Crystal AlN with NRIXS Joseph Bradley, Gerald Seidler, Rafael Dalmau, Kenneth Nagle, Zlatko Sitar A fundamental description of the mechanisms underlying the diverse applications of w-AlN requires a complete understanding of its short-range and long-range electronic structure. Here, we report momentum-transfer (q) dependent nonresonant inelastic x-ray scattering (NRIXS) measurements of single crystal w-AlN, surveying the low-energy plasmon regime, as well as the complex behavior at the Al K and L edges. This complete determination of the dynamic structure factor S(q,w) over a wide range of q and w both within and perpendicular to the basal plane allows for a uniquely detailed perspective on chemical bonding and low-energy electronic response in w-AlN. Our results are compared and contrasted with two independent ab initio theoretical treatments. [Preview Abstract] |
Monday, March 10, 2008 3:54PM - 4:06PM |
D37.00008: Optical properties of AlN epilayers probed by polarization resolved photoluminescence A. Sedhain, N. Nepal, M.L. Nakarmi, J.Y. Lin, H.X. Jiang, J.H. Edgar Polar and non-polar AlN homo- and hetero-epitaxial layers were grown on sapphire and AlN bulk substrates by metal organic chemical vapor deposition. Polarization resolved deep ultraviolet photoluminescence (PL) spectroscopy was employed to investigate the optical properties of these samples. For the first time, B and C valence band related free exciton (FX) transitions with a dominant \textbf{E}$_{- }$\textbf{c} polarization were directly observed from PL. The emission energy peaks of B and C excitons were found to locate at 199 and 212 meV higher than that of the A-exciton transition possessing the \textbf{E}$\vert $\textbf{c} polarization. A more comprehensive picture of the valence band structure of AlN is thus directly observed from PL measurements. AlN homo-epilayers in all orientations (a-, c-, and m-plane) were found to be strain free and have a nearly identical band gap of 6.099 eV at 10 K. The band edge peak intensity ratios of a-, c-, and m-plane homo-epilayers were roughly 32:5:1 and line width was found to be the smallest in a-plane homo-epilayer. Our results also indicated that built-in electric fields are almost absent in all AlN homo-epilayers. [Preview Abstract] |
Monday, March 10, 2008 4:06PM - 4:18PM |
D37.00009: Excitons in AlN under pressure. Niels E. Christensen, Robert Laskowski First-principles calculations based on solution of the Bethe-Salpeter equation of excitons in the high-pressure AlN phase show that a delocalization-localization transition occurs as additional pressure is applied. The transition, which is associated with a sudden increase in exciton binding energy, is related to a pressure-induced rearrangement of the energy bands. [Preview Abstract] |
Monday, March 10, 2008 4:18PM - 4:30PM |
D37.00010: Dresselhaus Effect in Bulk Wurtzite Structures Wan-Tsang Wang, Yia-Chung Chang, Jih-Chen Chiang, Yu-Chi Hsu The wurtzite bulk inversion asymmetry (WBIA) terms in the$k\cdot p$Hamiltonian have been derived from the linear combination of atomic orbital method, and the analytic form of Dresselhaus effect is obtained via an eight-band$k\cdot p$Hamiltonian. It is found that WBIA terms lead to not only a spin-degenerate line (along the kz axis) but also a minimum-spin-splitting surface. Furthermore, they can induce large spin splitting energies in wide-gap wurtzite materials such as GaN. Consequently, the D'yakonov-Perel' (DP) spin-relaxation mechanism can be effectively suppressed for all spin components in the [001] wurtzite quantum wells (QWs) at a resonance condition through appropriate sample design or the application of a suitable gate bias. Therefore, wurtzite QWs (e.g., InN/GaN or GaN/AlN) are potential candidates for spintronic devices such as the resonance spin lifetime transistor. [Preview Abstract] |
Monday, March 10, 2008 4:30PM - 4:42PM |
D37.00011: Optical phonon decay in GaN and AlN D. Y. Song, P. Pandit, A. Chandolu, M. Basavaraj, S. A. Nikishin, M. Holtz The intrinsic phonon decay properties of high-quality crystalline III-nitrides are found to be critical to device self-heating. An excellent approach for examining self-heating, as well as for understanding the properties of phonons, is micro-Raman scattering. This talk reports micro-Raman studies of the A$_{1}$(TO), E$_{1}$(TO), E$_{2}$2, A$_{1}$(LO), and E$_{1}$(LO) symmetry phonons of GaN and the A$_{1}$(TO), E$_{1}$(TO), E$_{2}$2 and A$_{1}$(LO) symmetry phonons of AlN from 13 to 375 K. By applying anharmonic decay theory to the observed temperature dependences of the phonon energies and linewidths, the phonon decay mechanisms of these zone-center vibrations have been determined. Thermal expansion is taken into account using published temperature-dependent coefficients. Both GaN and AlN A$_{1}$(TO) and E$_{1}$(TO) vibrations are described by symmetric two-phonon decay. The GaN E$_{2}$2 decays via creation of three phonons, however, the AlN E$_{2}$2 decays symmetrically into two phonons. The GaN and AlN LO bands are interpreted by an asymmetric two-phonon decay. Phonon lifetimes are obtained based on the observed linewidths, and the dependence allows us to estimate the intrinsic phonon life time for each vibration. The authors acknowledge support for this work by the National Science Foundation (ECS--0609416 and ECS--0304224) and the J. F Maddox Foundation. [Preview Abstract] |
Monday, March 10, 2008 4:42PM - 4:54PM |
D37.00012: ABSTRACT WITHDRAWN |
Monday, March 10, 2008 4:54PM - 5:06PM |
D37.00013: Large Optical Absorption Variation in Green GaInN/ GaN Multiply Quantum Well under High Charge Carrier Density. Wei Zhao, Mingwei Zhu, Yufeng Li, Yong Xia, Jayantha Senawiratne, Theeradetch Detchprohm, Christian Wetzel Blue GaInN/GaN multiple quantum well (MQW) light emitting diodes (LED) typically show a strong efficiency droop under high injection current density. The effect is even further pronounced for green LEDs. To identify the reason, 535nm emitting MQW epilayers were studied under a continuous wave high density photon excitation to simulate electrical injection conditions. Varying the excitation density over four orders of magnitude, the transmission and absorption were obtained. By comparing the signal of various sample structures, such as GaN/sapphire and full MQW/GaN/sapphire structures, the MQW effect could be isolated. At a wavelength of 514 nm and carrier injection density of 5 x 10$^{22}$ cm$^{-2}$ s$^{-1}$, the MQW showed an absorption enhancement as large as 20{\%}. Following a standard derivation procedure, a very large nonlinear absorption coefficient of 2.6 cm/W was derived. The enhancement of absorption may indicate a new recombination process that becomes effective under high carrier density. The effect could play a role in the observed efficiency droop of LEDs and play a major role in the limitations of GaInN/GaN laser diodes. This work was supported by DOE/NETL. [Preview Abstract] |
Monday, March 10, 2008 5:06PM - 5:18PM |
D37.00014: The influence of O$_{2}$ on the properties of InN thin films A. Dixit, C. Sudakar, J.S. Thakur, V.M. Naik, R. Naik, G. Lawes InN thin films often exhibit characteristics typical of degenerate semiconductors. This degenerate behavior is typically attributed to the inclusion of oxygen vacancies or the presence of structural defects. To help clarify this point, we studied the effect of O$_{2}$ in two different sputter deposited InN thin films. One film was prepared using pure In metal sputtered in an argon/nitrogen atmosphere and the other sample was prepared from an In$_{2}$O$_{3}$ target, which leads to incorporation of some oxygen in the resultant film. We studied the structural, optical and electronic properties of these films in detail. These measurements showed that even the small amount of O$_{2}$ from the oxide target, drastically affects the growth and structure of the InN film, resulting in polycrystalline samples. However, for both samples, the absorption spectra showed an optical band edge close to 1.84 eV with carrier concentration is $\sim $10$^{21}$ cm$^{-3}$ , showing the degenerate nature of both films. This study suggests that the degenerate nature of the InN films is unchanged on increasing the concentration of oxygen impurities or adding structural defects. [Preview Abstract] |
Monday, March 10, 2008 5:18PM - 5:30PM |
D37.00015: Effect of hydrogen on surface electron accumulation in InN films Rudra Bhatta, Brian Thoms, Mustafa Alevli, Nikolaus Dietz Effect of hydrogen on electron accumulation in InN films has been studied by high resolution electron energy loss spectroscopy. N-H loss features are observed in the HREEL spectra from the InN surface after atomic hydrogen cleaning. Heating for 30 s at 500$^{\circ}$C results in the disappearance of all adsorbate loss features indicating desorption of hydrogen and production of a bare InN surface. HREEL spectra taken from both bare and hydrogenated surfaces show a broad loss feature due to conduction band plasmon excitations. As the incident electron energy is decreased from 35 to 7 eV, which results in shorter penetration depths and increasing surface sensitivity, the energy of plasmon loss feature increases by 600 cm$^{-1}$ in spectra from both the bare and hydrogenated surfaces. The increase in plasmon loss energy with increasing surface sensitivity indicates higher carrier concentration on the surface, i.e. surface electron accumulation. This demonstrates that surface electron accumulation exists in the absence of surface indium overlayers or droplets and is unaffected by surface hydrogen adsorption. [Preview Abstract] |
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