Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session U43: Optical Properties of Quantum Well Systems |
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Sponsoring Units: DCMP Chair: Sergio Ulloa, Ohio University Room: Colorado Convention Center 506 |
Thursday, March 8, 2007 8:00AM - 8:12AM |
U43.00001: $\Gamma$-phonons in ZnSe(C$_{2}$H$_{8}$N$_{2}$)$_{1/2}$ and ZnTe(C$_{2}$H$_{8}$N$_{2}$)$_{1/2}$ hybrid materials Ivan Naumov, Huaxiang Fu Artificially synthesized organic/inorganic hybrid materials with semiconductor component are of growing interest due to potential applications in flexible microelectronics. Among them, hybrid ZnSe(C$_{2}$H$_{8}$N$_{2}$)$_{1/2}$ and ZnTe(C$_{2}$H$_{8}$N$_{2}$)$_{1/2}$ are two examples capable of tuning electronic and optical properties on a wide range. Engineering of these materials is difficult without deeper understanding of their fundamental physical characteristics, including electronic band structure and phonon spectra. Recent experimental investigations [1] performed on $\beta$--ZnTe(C$_{2}$H$_{8}$N$_{2}$)$_{1/2}$ samples and showed multiple sharp phonon modes in frequencies very different from the LO($\Gamma$) phonon of the binary semiconductor ZnTe. Motivated by these results, we have performed density-functional calculations of the $\Gamma$ phonon modes for both $\alpha$-- and $\beta$--phases of ZnSe(C$_{2}$H$_{8}$N$_{2}$)$_{1/2}$ and ZnTe(C$_{2}$H$_{8}$N$_{2}$)$_{1/2}$. We found, in particular, that light hydrogen atoms not only define the high frequency motion (1500--3000 cm$^{-1}$), but also dominate in some low frequency modes in the region of 100--150 cm$^{-1}$ where they move mostly perpendicular to the superlattice stacking direction. Based on symmetry of the materials, the Raman modes at the $\Gamma$ point are identified. \newline [1] X. Huang, J. Li, Y. Zhang, and A. Mascarenhas, J. Am. Chem. Soc. {\bf 125}, 7049 (2003). [Preview Abstract] |
Thursday, March 8, 2007 8:12AM - 8:24AM |
U43.00002: The Magnetic-Field Dependent Phonon-Like FIR Absorption in Modulation Doped CdMnTe/CdMgTe quantum Well Structures. Li-Chun Tung, Grzegorz Karczewski, Yong-Jie Wang Spin-dependent phonon had been reported in several magnetic semiconductors. This unique phonon mode is resulted from an ion-position dependent spin Hamiltonian. This mode can be either infrared or Raman active. However, such modes were never observed in the diluted magnetic semiconductors. We have investigated a series of CdMnTe/CdMgTe QW samples with Mn concentration ranged from 0 to 3.9{\%} up to 33T and found an IR absorption near 125cm$^{-1}$. The intensity of this mode increases rapidly with increasing magnetic field, while the energy increases only several wavenumbers. This behavior resembles that of the spin-dependent phonon mode. The unique behavior of the spin-dependent phonon mode was induced by a magnetic transition with decreasing temperatures. In the current studies, however, similar behavior is induced by applying magnetic field. Besides 125cm$^{-1}$ mode, we have also observed two new IR absorptions in addition to the electron cyclotron resonance (CR). The intriguing disappearance of CR at high magnetic field and the stimulating behavior of these two new modes will be discussed. [Preview Abstract] |
Thursday, March 8, 2007 8:24AM - 8:36AM |
U43.00003: ABSTRACT WITHDRAWN |
Thursday, March 8, 2007 8:36AM - 8:48AM |
U43.00004: Investigation of the influence of the magnetic field of different orientations on excitonic states in structures with shallow quantum wells Yuri Khavin, Mikhail Skorikov, Nikolai Sibeldin, Vitaliy Tsvetkov Photoluminescence (PL) and photoluminescence excitation (PLE) spectra of GaAs/Al$_{0.5}$Ga$_{0.95}$As structures with two tunneling-coupled quantum wells (QWs) 3 and 4 nm wide and structures with tunneling-isolated QWs of the same width were investigated at liquid helium temperatures in parallel and perpendicular magnetic fields up to 14.6T. It was shown that the parallel magnetic field strongly suppresses tunneling coupling in the structure with coupled QWs, and its PLE spectrum in a strong field becomes similar to the PLE spectrum of the structure with isolated QWs. At the same time, excitonic components of the PL spectrum do not undergo such substantial changes. It was also shown that both parallel and perpendicular field substantially affect the intensity of the trion PL line in both structures, but the influence of the parallel field is much stronger than it is for the perpendicular field. [Preview Abstract] |
Thursday, March 8, 2007 8:48AM - 9:00AM |
U43.00005: Photoluminescence Studies of Type-I and Type-II In$_{0.27}$Ga$_{0.73}$Sb/In$_{x}$Al$_{1-x}$As$_{y}$Sb$_{1-y}$ Multiple Quantum Well Heterostructures Grown by MBE E.R. Glaser, R. Magno, B.V. Shanabrook, J.G. Tischler Heterojunction bipolar transistors (HBTs) with lattice constant near 6.2{\AA} using the InAs/AlSb/GaSb family of semiconductors are of interest based on their promise for high-speed operation with low power dissipation. A unique aspect of these materials is the ability to engineer the bandgap energies and the conduction band offsets at the emitter/base and base/collector heterointerfaces by varying the In/Al and Al/Sb ratios. In this work low-temperature PL was performed on a set of In$_{0.27}$Ga$_{0.73}$Sb/In$_{x}$Al$_{1-x}$As$_{y}$Sb$_{1-y}$ MQW heterostructures to provide a measure of the conduction band offsets ($\Delta _{CB})$ that are a critical design parameter for the HBTs. Excitation power studies revealed evidence for strong recombination at 0.56 eV within the InGaSb layers of the MQW structure with x,y = 0.52,0.25 and, thus, confirmed the type-I band alignment. In contrast, weaker PL bands at energies close to 0.4 eV and that exhibited strong shifts with increasing excitation power density were found from the nominally type-II MQW samples with x,y=0.67,0.39 and 0.69,0.41. Neglecting small corrections ($\sim $15 meV) due to the electron and hole confinement energies, we estimate $\Delta _{CB}$ of $\sim $ 120-150 meV in these Type-II structures. [Preview Abstract] |
Thursday, March 8, 2007 9:00AM - 9:12AM |
U43.00006: Temperature and Pump Pulse Dependence of Superfluoresence from InGaAs/GaAs Multiple Quantum Well in High Magnetic Fields Xiaoming Wang, Young-Dahl Jho, Jinho Lee, David Reitze, Junichiro Kono, Alexey Belyanin, Vitaly Kocharovsky, Glenn Solomon, Xing Wei, Stephen McGill Using intense near-IR ultrashort pulse laser excitation, we investigate the characteristics of cooperative emission (superfluoresence) from dense electron hole magneto-plasmas in InGaAs/GaAs MQW in high magnetic fields as a function of temperature and excitation pulsewidth. We find strong narrow line emissions from 0-0 and 1-1 Landau levels (LLs), with thresholds depending on magnetic field and temperature. Varying the excitation pulsewidth (180 fs -- 60 ps) and fluence (0.1 -- 1 mJ/cm$^{2})$, we observe qualitative changes in the emission strengths from different LLs. The strong emissions from 0-0 and 1-1 LL excited with short and long pulses are obviously different. Mechanisms of the temperature and excitation pulse width effect on the strong emission are presented. [Preview Abstract] |
Thursday, March 8, 2007 9:12AM - 9:24AM |
U43.00007: Interface roughness scattering in p-Si/SiGe asymmetric quantum wells Marco Califano, N.Q. Vinh, P.J. Phillips, Z. Ikonic, R.W. Kelsall, P. Harrison, C.R. Pidgeon, B.N. Murdin, D.J. Paul, P. Townsend, J. Zhang, I.M. Ross, A.G. Cullis Of paramount importance in the design of a quantum cascade laser is the ability to engineer carrier lifetimes. These can be strongly influenced by the quality of the interfaces: fluctuations in the well width result in local fluctuations of the carriers' confining potential, which act as a scattering potential. We report the direct determination of non-radiative lifetimes in Si/SiGe asymmetric quantum wells designed to access spatially indirect interwell transitions between heavy-hole states, at photon energies below the optical phonon energy. We show both experimentally and theoretically that, for the interface quality currently achievable experimentally interface roughness will dominate all other scattering processes up to about 200 K. By comparing our results obtained for two different structures we deduce that in this regime both barrier and well widths play an important role in the determination of the carrier lifetime. Comparison with recent data for III-V multiple quantum wells leads us to the conclusion that the dominant role of interface roughness scattering at low temperature found here is a general feature of a wide range of semiconductor heterostructures not limited to IV-IV materials. [Preview Abstract] |
Thursday, March 8, 2007 9:24AM - 9:36AM |
U43.00008: Localized charged magnetoexcitons in 2D systems Diana Cosma, Alexander Todd, Alexander Dzyubenko, Andrey Sivachenko We performed a detailed theoretical study of localization of spin-singlet $X_s ^-$ and spin-triplet $X_t ^-$ negatively charged excitons on isolated charged donors $D^+$ located at various distances $L$ from the heteroboundary of a Quantum Well (QW). Our results show that the parent bright singlet state $X_s ^-$ remains always bound. In contrast, the dark $X_{td} ^-$ and bright $X_{tb} ^-$ triplet states survive only for sufficiently large distances $L$ to the donor ion $D^+$. In the presence of the $D^+$ the dark triplet acquires finite oscillator strengths. We also found several new bound $X^-$ states, some of which have surprisingly large oscillator strengths. We showed that shake-up processes are strictly prohibited in magneto-photoluminescence of free charged excitons and only become allowed in the presence of a $D^+$ or other symmetry-breaking mechanisms. Our results show that the main magneto-PL peaks of free and donor bound charged excitons may exhibit very similar features while the shake-up processes in PL are symmetry-breaking signatures. [Preview Abstract] |
Thursday, March 8, 2007 9:36AM - 9:48AM |
U43.00009: Effect of disorder on the lifetime of interface polaritons Igor Smolyarenko, Celestino Creatore, Alexei Ivanov We study the effects of weak disorder on the liftime of interface polaritons in quantum wells (QWs) associated with in- plane free QW excitons. In ideal quantum wells, the interface light is evanescent, i.e., it is localized in the z direction (QW growth direction) and is thus invisible at macroscopic distances from the QD plane. However, randomness in the structure of QWs leads to finite radiative lifetimes of the interface light modes which makes them ``visible'' in time- resolved light scattering experiments. We study the distribution of the delay times for scattering of bulk photons off the two- dimensional interface layer at finite incidence angle. While the bulk of the distribution corresponds to the usual threshold effect, the tail of the distribution at long delay times is governed by the quasi-resonant long-lived interface light modes which are essentially the disorder-degraded remnants of the evanescent waves in ideal QWs. These modes are analogous in some ways to the anomalously localised states in two-dimensional disordered electronic systems. Time-resolved spectroscopy of weakly disordered QWs is thus shown to be an effective tool for probing the ``hidden'' optics of the interface polaritons. [Preview Abstract] |
Thursday, March 8, 2007 9:48AM - 10:00AM |
U43.00010: Generic Theory of Surface Plasmon Polaritons at Active or Passive Metal-Dielectric Interfaces Dentcho Genov, Muralidhar Ambati, Xiang Zhang In this work we propose a simple analytical approach to study the excitation of surface plasmon polaritons (SPP) at the interfaces between metals and passive or active media. Explicit relationships are derived for both SP dispersion and propagation length. The analytical theory matches the exact numerical calculations for a wide range of excitation frequencies and metal slab thicknesses. Scaling relationships for the critical gain required to achieve infinite propagation length are derived for the symmetric and antisymmetric SPP modes. A specific multiple quantum well (MQW) system is identified as an effective media for prospective experimental studies of SP amplification and enhanced propagation. [Preview Abstract] |
Thursday, March 8, 2007 10:00AM - 10:12AM |
U43.00011: Nonequilibrium Green's function modelling of quantum well solar cells Urs Aeberhard, Rudolf H. Morf We present a microscopic model of the photocurrent in $GaAs-AlGaAs$ quantum well solar cells (QWSC), based on the nonequilibrium Green's function formalism (NEGF) for a multiband tight binding Hamiltonian. The quantum kinetic equations of motion are selfconsistently coupled to Poisson's equation. Relaxation and broadening mechanisms are considered by the inclusion of acoustic and optical electron-phonon interaction in a self consistent Born approximation of the scattering selfenergies. The model is applied to different multi-quantum-well sytems to investigate the role of device geometry and coupling between the wells. [Preview Abstract] |
Thursday, March 8, 2007 10:12AM - 10:24AM |
U43.00012: Optical and Electronic Properties of Electrochemically Active Perylene Tetracarboxylic Diimide Molecules Nazanin Davani, ken Shimizu, Michael Preiner, Nicholas Melosh Perylene tetracarboxylic diimide (PTCDI) molecules form a unique class of n-type semiconductors with high thermal and photo stability. Understanding the electronic properties of these molecules in nanoscale systems may lead to novel applications in various molecular electronics devices. Using optical spectroscopy, we analyzed the optical and electronic properties of electrochemically active TE-PTCDI molecules self -assembled on gold electrodes. Surface Plasmon Resonance Spectroscopy is used to detect the refractive index of the monolayer. Cyclic voltammetry and SPR measurements are performed simultaneously to probe changes in reflectivity as the molecule undergoes redox reactions. In addition, the TE-PTCDI molecule is used in fabricating metal-insulating monolayer-metal devices using Polymer Assisted Lift Off (PALO) technique. The influence of the top metal contact on molecular properties will be discussed. [Preview Abstract] |
Thursday, March 8, 2007 10:24AM - 10:36AM |
U43.00013: Photoconductivity of Yttrium Neodymium Gadolinium Oxalate Crystals Soosy Kuryan, Rosalin Abraham, Jayakumari Isac Crystals are pillars of modern technology..Yttrium Neodymium Gadolinium oxalate (YNdGaOx) crystals were grown by gel method by the diffusion of Yttrium Chloride, Neodymium Chloride, and Gadolinium Chloride into the set gel containing Oxalic acid. Silica gel method is capable of yielding crystals of high optical perfection and wide morphology. The growing crystals are held in the gel medium in a strain free manner and at the same time nucleation and super saturation are well controlled. Photo conductivity studies of these crystals revealed negative photoconductivity nature. The photocurrent is found to be less than the dark current at every applied electric field. Rare Earth compounds are known for their interesting electric, magnetic and luminescent properties. Recent investigations on the fluorescence of some rare earth oxalates suggest their potentiality for their optical applications. Rare Earth oxalates evoked greater attention because of their ionic conduction. [Preview Abstract] |
Thursday, March 8, 2007 10:36AM - 10:48AM |
U43.00014: Plasmon dispersion and Coulomb drag in low-density electron bi-layers S. M. Badalyan, C. S. Kim, G. Vignale, G. Senatore We investigate the effect of exchange and correlation (xc) on the plasmon spectrum and the Coulomb drag between spatially separated low-density two-dimensional electron layers. We adopt a new approach, which employs dynamic xc kernels in the calculation of the bi-layer plasmon spectra and of the plasmon-mediated drag, and static many-body local field factors in the calculation of the particle-hole contribution to the drag. We observe that both optical and acoustical plasmon modes are strongly affected by xc corrections and shift in opposite directions with decreasing density. This is in stark contrast with the tendency observed within the random phase approximation (RPA). We find that the introduction of xc corrections results in a significant enhancement of the transresistivity and qualitative changes in its temperature dependence. In particular, the large high-temperature plasmon peak that is present in the RPA is found to disappear when the xc corrections are included. Our numerical results are in good agreement with the results of recent experiments by M. Kellogg {\it et al.}, Solid State Commun. \textbf{123}, 515 (2002). [Preview Abstract] |
Thursday, March 8, 2007 10:48AM - 11:00AM |
U43.00015: Surface Plasmon Polaritons on Concentric Cylindrical Shells Jakub Pritz, Lilia Woods A theoretical investigation of electromagnetic plasmon modes for multilayered concentric cylindrical shells in the absence of an applied magnetic field is presented. The plasmon excitations in such multiple interface configurations are characterized by the electromagnetic fields. To obtain the dispersion relation for the modes, the Maxwell equations with appropriate boundary conditions are solved numerically. We study the conditions for existence of radiative and nonradiative modes. The effects of varying the different shells radii, their thicknesses and dielectric response functions are also investigated. The physical importance of the different plasmon modes is also discussed. [Preview Abstract] |
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