Tuning of the Electron Spin Relaxation Anisotropy via Optical Gating in GaAs/AlGaAs Quantum Wells

The carrier-density-dependent spin relaxation dynamics for modulation-doped GaAs/Al_(0.3)Ga_(0.7)As quantum weiis is studied using the time-resolved magneto-Kerr rotation measurements.The electron spin relaxation time and its in-plane anisotropy are studied as a function of the optically injected electron density.Moreover,the relative strength of the Rashba and the Dresselhaus spin-orbit coupling fields,and thus the observed spin relaxation time anisotropy,is further tuned by the additional excitation of a 532 nm continuous wave laser,demonstrating an effective spin relaxation manipulation via an optical gating method.     

Two-dimensional electron-hole pair diffusivities in thin GaAs/AlGaAs Quantum Wells

Diffusivities of two-dimensional electron-hole pairs in thin GaAs/AlGaAs Quantum Wells (QWs) are studied experimentally and theoretically as functions of temperature and well-width. With growing well-widths, increasing diffusivities are observed for fixed Al-contents. Experimental diffusivities for the lateral carrier motion in continuously as well as in interrupted-grown thin QWs of different barrier Al-content are presented for T>150 K. Increasing diffusivities are observed for rising temperatures in the range T190 K. A comparison of the experimental data and results of theoretical model calculations indicates that the increase is partly related to thermal dissociation of excitons into free carrier pairs. The effective diffusivity of this two-component system is calculated using a system of rate equations and considering acoustic-deformation-potential scattering, polar-optical scattering and barrier-alloy-disorder scattering.The experimental data were obtained at: 4. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, W-7000 Stuttgart 80, Germany     

基于GaAs-AlGaAs非对称耦合量子阱材料的半导体弱光开关

提出了一种基于在GaAs-AlGaAs非对称耦合量子阱材料子带跃迁的量子干涉的半导体弱光开关，分析了驰豫速率γ21对光开关的影响，这种半导体弱光开关是半导体超晶格材料共振隧穿作用导致的子带跃迁的Fano干涉的结果，由于半导体结构与材料可以人为地选择，相干强度可以控制和改变，这种半导体弱光开关比采用原子系统更实用，这也是一种在半导体材料中实现一束光控制另一束光的方法。     

Quantum cascade electroluminescence in GaAs/AlGaAs structures

The operation of a unipolar quantum cascade light-emitting diode based on the material system GaAs/AlGaAs is reported. The LED operates at a wavelength of 6.9 μm. Detailed analysis of the electroluminescence spectra shows a linewidth as narrow as 14 meV at cryogenic temperatures, increasing to 20 meV at room temperature. For typical drive-current densities of 1 kA/cm² the optical output power lies in the ten 10 nW range. Additional absorption and photocurrent measurements provide a complete characterization of the mid-infrared emitter.     

Piezoelectric Relaxation of Two-Dimensional Electron Gas in Heterostructures with InGaN/GaN Quantum Wells

Russian Physics Journal - The article is devoted to the study of the mechanism of piezoelectric scattering of charge carriers in InGaN/AlGaN/GaN heterostructures with one filled size quantization...     

Spin Transport under In-plane Electric Fields with Different Orientations in Undoped InGaAs/AlGaAs Multiple Quantum Wells

The spin-polarized photocurrent is used to study the in-plane electric field dependent spin transport in undoped InGaAs/AlGaAs multiple quantum wells. In the temperature range of 77–297 K, the spin-polarized photocurrent shows an anisotropic spin transport under different oriented in-plane electric fields. We ascribe this characteristic to two dominant mechanisms: the hot phonon effect and the Rashba spin-orbit effect which is influenced by the in-plane electric fields with different orientations. The formulas are proposed to fit our experiments, suggesting a guide of potential applications and devices.     

High-Power and Low-Threshold-Current-Density GaAs/AlGaAs Quantum Cascade Lasers

We report on the realization of GaAs/AlGaAs quantum cascade lasers with an emission wavelength of 9.1 μm above the liquid nitrogen temperature. With optimal current injection window and ridge width of 24 and 60μm respectively, a peak output power more than 500mW is achieved in pulsed mode operation. A low threshold current density Jth = 2.6 kA/cm^2 gives the devices good lasing characteristics. In a drive frequency of i kHz, the laser operates up to 20% duty cycle.     

Spin Splitting in Different Semiconductor Quantum Wells

We theoretically investigate the spin splitting in four undoped asymmetric quantum wells in the absence of external electric field and magnetic field. The quantum well geometry dependence of spin splitting is studied with the Rashba and the Dresselhaus spin-orbit coupling included. The results show that the structure of quantum well plays an important role in spin splitting. The Rashba and the Dresselhaus spin splitting in four asymmetric quantum wells are quite different. The origin of the distinction is discussed in this work.     

Anisotropic Spin Splitting in Step Quantum Wells

By the method of finite difference, the anisotropic spin splitting of the AlxGa1-xAs/GaAs/Aly Ga1-yAs/AlxGal-xAs step quantum wells （QWs） are theoretically investigated considering the interplay of the bulk inversion asymmetry and structure inversion asymmetry induced by step quantum well structure and external electric field. We demonstrate that the anisotropy of the total spin splitting can be controlled by the shape of the QWs and the external electric field. The interface related Rashba effect plays an important effect on the anisotropic spin splitting by influencing the magnitude of the spin splitting and the direction of electron spin. The Rashba spin splitting presents in the step quantum wells due to the interface related Rashba effect even without external electric field or magnetic field.     

Two-Dimensional GaAs/AlGaAs Multiple Quantum Well Spatial Light Modulators

Multiple quantum well spatial light modulators with 128x128 array in 38μm pitch are fabricated using two pproaches, one with an attachment of an optical substrate and another one without. These two fabrication processes are described and compared.     

Electron spin filtering in the GaAs/AlGaAs interface space charge field

The circularly polarized recombination radiation produced by optically oriented electrons in GaAs and viewed in the direction of and opposite to the pump light propagation was found to have opposite signs of polarization. The excitation was effected by photons of energy E_hv ≈ E _g + Δ through a transparent AlGaAs window. The opposite signs of circular polarization and its complex dependence on the luminescence wavelength are accounted for by the influence of the space charge field created by the depleted layer near the interface.     

Spin excitations in few-electrons AlGaAs/GaAs quantum dots probed by inelastic light scattering

We present recent studies of electronic excitations in nanofabricated AlGaAs/GaAs semiconductor quantum dots (QDs) by resonant inelastic light scattering. The resonant light scattering spectra are dominated by excitations from parity-allowed inter-shell transitions between Fock–Darwin levels. In QDs with very few electrons the resonant spectra are characterized by distinct charge and spin excitations that reveal the strong impact of both exchange and correlation effects. A sharp inter-shell spin excitation of the triplet spin QD state with four electrons is identified.     

Fine Structure of Levels and Piezospectroscopy of A<Superscript>+</Superscript> Centers in GaAs/AlGaAs Quantum Wells

Experimental and theoretical piezospectroscopic investigation of A⁺ centers in GaAs/AlGaAs quantum wells doped with beryllium is presented. Spectra of linearly polarized photoluminescence are studied experimentally depending on applied uniaxial pressure. A model of the A⁺ center in the quantum well in the presence of uniaxial deformation in the plane of the quantum well has been constructed. Analytical expressions for the level energy, optical transition intensities, and polarization ratio have been obtained. In the framework of the proposed theory, the experimentally observed change in the polarization ratio depending on pressure and the shift of the line maximum towards short waves are explained.     

Spin relaxation in GaAs/AlGaAs quantum wells in the vicinity of odd filling factors

Electron spin resonance in GaAs/AlGaAs quantum wells in the vicinity of odd filling factors ν = 3, 5, and 7 is investigated. The spin relaxation time of two-dimensional electrons is determined from the width of the microwave resonance absorption line. Dependences of the spin relaxation time on the filling factor, temperature, and orientation of the magnetic field are investigated. The spin relaxation time decreases noticeably upon deviation from odd filling factors, and its maximum value depends on the angle between the magnetic field and the plane of the two-dimensional electron gas.     

Spin Relaxation of Electrons in Single InAs Quantum Dots

By using polarization-resolved photoluminescence spectra, we study the electron spin relaxation in single InAs quantum dots （QDs） with the configuration of positively charged excitons X＋ （one electron, two holes）. The spin relaxation rate of the hot electrons increases with the increasing energy of exciting photons. For electrons localized in QDs the spin relaxation is induced by hyperfine interaction with the nuclei. A rapid decrease of polarization degree with increasing temperature suggests that the spin relaxation mechanisms are mainly changed from the hyperfine interaction with nuclei into an electron-hole exchange interaction.     

Dependences of the Transport Scattering Time and Quantum Lifetime on the Two-Dimensional Electron Gas Density in Modulation-Doped Single GaAs Quantum Wells with AlAs/GaAs Short-Period Superlattice Barriers

JETP Letters - The dependences of the transport scattering time τt, quantum lifetime τq, and their ratio τt/τq on the density ne of the electron gas in modulation-doped single...