Tuning of conduction intersublevel absorption wavelengths in (In, Ga)As/GaAs quantum-dot nanostructures

We demonstrate that by increasing the amount of (In, Ga)As deposit in a quantum dot layer, the intersublevel absorption wavelength for (In, Ga)As/GaAs quantum-dot infrared photodetectors can be blue-shifted from 15 to 10 mu m while the photoluminescence peak is red-shifted. We directly compare the measured energy spacing between intersublevels obtained from infrared absorption spectroscopy with those obtained from photoluminescence spectroscopy. We find that the intersublevel energy spacing determined from absorption measurements is much larger than that obtained from the photoluminescence measurements. (C) 2000 American Institute of Physics. [S0003-6951(00)04524-1].

Strain and photoluminescence characterization of cubic (In,Ga)N films grown on GaAs(001) substrates

Cubic InxGa1-xN films were successfully grown on GaAs(001) substrates by metalorganic chemical-vapor deposition. The values of x content ranging from 0.10 to 0.24 obtained at different growth conditions were measured by double-crystal x-ray diffraction (XRD). The perpendicular and parallel elastic strain of the In0.2Ga0.8N layer, epsilon(perpendicular to)=0.4% and epsilon(parallel to)=-0.4% for GaN and epsilon(perpendicular to)=0.37% and epsilon(parallel to)=-0.37% for InGaN, respectively, were derived using the XRD measurements. The inhomogeneous strain and the average grain size of the In0.2Ga0.8N/GaN films were also studied by XRD. Photoluminescence spectra were used to measure the optical characterization of the InxGa1-xN thin films with different In composition, and the near-band-edge emission dependence of cubic InxGa1-xN on the x value is nearly linear with In content x less than or equal to 0.24. (C) 2000 American Institute of Physics. [S0021-8979(00)03908-6].

Normal-incidence intersubband (In, Ga)As/GaAs quantum dot infrared photodetectors

We report the device performance of normal-incidence (In, Ga)As/GaAs quantum dot intersubband infrared photodetectors. A primary intersubband transition peak is observed at the wavelength of 13 mu m (E-0 --> E-1) and a secondary peak at 11 mu m (E-0 --> E-2). The measured energy spacing in the conduction band of the quantum dots is in good agreement with low temperature photoluminescence measurement and calculations. A peak detectivity of 1 x 10(10) cm Hz(1/2)/W at 13 mu m was achieved at 40 K for these devices. (C) 1998 American Institute of Physics. [S0003-6951(98)01440-5].

Tunneling magnetoresistance in (Ga,Mn)As/Al-O/CoFeB hybrid structures

Tunneling magnetoresistance (TMR) in Ga(0.9)2Mn(0.08)As/Al-O/Co40Fe40B20 trilayer hybrid structure as a function of temperature from 10 to 50 K with magnetic field vertical bar H vertical bar <= 2000 Oe has been studied. TMR ratio of 1.6% at low fields at 10 K was achieved with the applied current of 1 mu A. The behavior of junction resistance was well explained by the tunneling resistance across the barrier. Strong bias dependences of magnetoresistance and junction resistance were presented. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3068418]

Growth Parameter Dependence of Structural Characterizations of Diluted Magnetic Semiconductor (Ga, Cr)As

We report the influence of growth parameters and post-growth annealing on the structural characterizations and magnetic properties of (Ga, Cr)As films. The crystalline quality and magnetic properties are sensitive to the growth conditions. The single-phase (Ga, Cr)As film with the Curie temperature of 10 K is synthesized at growth temperature T-s = 250 degrees C and with nominal Cr content x = 0.016. However, for the films with x > 0.02, the aggregation of Cr atoms is strongly enhanced as both T. and x increase, which not only brings strong compressive strain in the epilayer, but also roughens the surface. The origin of room-temperature ferromagnetism in (Ga, Cr)As films with nanoclusters is also discussed.

MVPE Ga 掺杂ZnO 薄膜材料的制备及其在LED 中的应用

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Temperature dependent photoluminescence of an In(Ga)As/GaAs quantum dot system with different areal density

We have systematically studied the temperature dependent photoluminescence of a self-assembled In(Ga)As/GaAs quantum dot (QD) system with different areal densities from similar to 10(9) to similar to 10(11) cm(-2). Different carrier channels are revealed experimentally and confirmed theoretically via a modified carrier equation model considering a new carrier transfer channel, i.e. continuum states ( CS). The wetting layer is demonstrated to be the carrier quenching channel for the low-density QDs but the carrier transfer channel for the high-density QDs. In particular, for the InGaAs/GaAs QDs with a medium density of similar to 10(10) cm(-2), the CS is verified to be an additional carrier transfer channel in the low temperature regime of 10-60 K, which is studied in detail via our models. The possible carrier channels that act on different temperature regimes are further discussed, and it is demonstrated that density is not a crucial factor in determining the carrier lateral coupling strength.

一种基于Messy GA���结构测试数据自动生成方法

结构性测试是标识测试用例的基本方法之一．由于程序语言的复杂性以及被测程序的多样性，自动生成结构测试数据的一种有效方法是根据程序运行结果指导生成过程，通过不断迭代，生成符合要求的测试数据集．提出一种基于Messy GA���结构测试数据自动生成方法，将测试覆盖率表示为测试输入集X的函数F（X），并利用Messy GA���需要染色体模式排列的先验知识即可进行优化求解的性质对F（X）的进行迭代寻优，进一步提高了搜索的并行性，并最终提高测试覆盖率．对一组标准测试程序和若干实际应用程序的实验结果表明，较之现有基于遗传算法的生成方法，该方法能够以更高的效率生成更高质量的测试数据，并适用于较大规模的程序．

PRESSURE-DEPENDENCE OF PHOTOLUMINESCENCE IN IN(X)GA(1-X)AS/AL(Y)GA(1-Y)AS STRAINED QUANTUM-WELLS WITH DIFFERENT WIDTH

A systematic investigation on the photoluminescence (PL) properties of InxGa1-xAs/AlyGa1-xAs (x = 0.15, y = 0, 0.33) strained quantum wells (SQWs) with well widths from 1.7 to 11.0 nm has been performed at 77 K under high pressure up to 40 kbar. The experimental results show that the pressure coefficients of the exciton peaks corresponding to transitions from the first conduction subband to the heavy-hole subband increase from 10.05 meV/kbar of 11.0 nm well to 10.62 meV/kbar of 1.8 nm well for In0.15Ga0.85As/GaAs SQWs. However, the corresponding pressure coefficients slightly decrease from 9.93 meV/kbar of 9.0 nm well to 9.73 meV/kbar of 1.7 nm well for In0.15Ga0.85As/Al0.33Ga0.67As SQWs. Calculations based on the Kronig-Penney model reveal that the increased or decreased barrier heights and the increased effective masses with pressure are the main reasons of the change in the pressure coefficients.

Lateral periodicity in highly-strained (GaIn)As/Ga(PAs) superlattices investigated by X-ray scattering techniques

In this work we investigate the lateral periodicity of symmetrically strained (GaIn)As/GaAs/Ga(PAs)/GaAs superlattices by means of X-ray scattering techniques. The multilayers were grown by metalorganic Vapour phase epitaxy on (001)GaAs substrates, which were intentionally off-oriented towards the [011]-direction. The substrate off-orientation and the strain distribution was found to affect the structural properties of the superlattices inducing the generation of laterally ordered macrosteps. Several high-resolution triple-crystal reciprocal space maps, which were recorded for different azimuth angles in the vicinity of the (004) Bragg diffraction and contour maps of the specular reflected beam collected in the vicinity of the (000) reciprocal lattice point, are reported and discussed. The reciprocal space maps clearly show a two-dimensional periodicity of the X-ray peak intensity distribution which can be ascribed to the superlattice periodicity in the direction of the surface normal and to a lateral periodicity in a crystallographic direction coinciding with the miscut orientation. The distribution and correlation of the vertical as well as of the lateral interface roughness was investigated by specular reflectivity and diffuse scattering measurements. Our results show that the morphology of the roughness is influenced by the off-orientation angle and can be described by a 2-dimensional waviness.

Structural ordering and interface morphology in symmetrically strained (GaIn)As/Ga(PAs) superlattices grown on off-oriented GaAs(100)

In this work we investigate the structural properties of symmetrically strained (GaIn)As/GaAs/Ga(PAs)/GaAs superlattices by means of x-ray diffraction, reciprocal-space mapping, and x-ray reflectivity. The multilayers were grown by metalorganic vapor-phase epitaxy on (001) GaAs substrates intentionally off-oriented towards one of the nearest [110] directions. High-resolution triple-crystal reciprocal-space maps recorded for different azimuth angles in the vicinity of the (004) Bragg diffraction clearly show a double periodicity of the x-ray peak intensity that can be ascribed to a lateral and a vertical periodicity occurring parallel and perpendicular to the growth surface. Moreover, from the intensity modulation of the satellite peaks, a lateral-strain gradient within the epilayer unit cell is found, varying from a tensile to a compressive strain. Thus, the substrate off-orientation promotes a lateral modulation of the layer thickness (ordered interface roughness) and of the lattice strain, giving rise to laterally ordered macrosteps. In this respect, contour maps of the specular reflected beam in the vicinity of the (000) reciprocal lattice point were recorded in order to inspect the vertical and lateral interface roughness correlation, A semiquantitative analysis of our results shows that the interface morphology and roughness is greatly influenced by the off-orientation angle and the lateral strain distribution. Two mean spatial wavelengths can be determined, one corresponding exactly to the macrostep periodicity and the other indicating a further interface waviness along the macrosteps. The same spatial periodicities were found on the surface by atomic-force-microscopy images confirming the x-ray results and revealing a strong vertical correlation of the interfaces up to the outer surface.

Photoluminescence studies of GaAs/AlGaAs single quantum well intermixed by Ga+ ion implantation

Ga(+)ion implantation followed by rapid thermal annealing (RTA) was used to enhance the interdiffusion in GaAs/AlGaAs single Quantum Wells(SQWs). The extent of intermixing was found to be dependent on the well depth, number of implanted ions and annealing time. A very fast interdiffusion process occurs at the initial annealing stage. After that, the enhanced diffusion coefficient goes back to the umimplanted value. We propose a two-step model to explain the diffusion process as a function of the annealing time : a fast diffusion process and a saturated diffusion process. The interdiffusion coefficient of the fast diffusion was found to be of well depth dependence and estimated to be in the range of 5.4x10(-16) similar to 1.5x10(-15)cm(2)s(-1). Copyright (C) 1996 Published by Elsevier Science Ltd