高组份Al值的AlxGa1-x As和AlxGa1-x As/GaAs/AlxGa1-xAs/GaAs多层结构的MOCVD生长

用自制常压MOCVD系统,在半绝缘GaAs衬底上生长高Al组份Al_xGa_1-xAs（其x值达0.83）,和Al_xGa_1-xAs/GaAs/Al_xGa_1-xAs/GaAs多层结构,表面镜面光亮。生长层厚度从几十到十几μm可控,测试表明外延层晶格结构完整,x值调节范围宽,非有意掺杂低,高纯GaAs外延层载流子浓度n_300K=1.7×10¹⁵cm^-3,n_77K=1.4×10¹⁵cm^-3,迁移率μ_300K=5900cmcm²/V.S,μ_77K=55500cm²/V.S。用电子探针,俄歇能谱仪测不出非有意掺杂的杂质,各层间界面清晰平直。 对GaAs,AlGaAs生长层表面缺陷,衬底偏角生长温度及其它生长条件也进行了初步探讨。     

Energy levels of single nonabrupt GaAs/AlxGa1-xAs quantum wells

Energy levels of electrons in nonabrupt GaAs/Al_xGa_1-xAs single quantum wells are calculated with and beyond the constant interfacial effective mass approximation (CIEMA), and compared with those of abrupt GaAs/Al_xGa_1-xAs quantum wells. For a given interface width, the energy levels calculated with the CIEMA are higher than those calculated beyond it, but both are higher than those of the abrupt semiconductor quantum well. The shifts of the energy levels increase with the interfacial width of the nonabrupt quantum well, as well as with the degree of interfacial asymmetry.     

Light scattering in GaAs parabolic quantum wells

We report the observation of electronic light scattering in photoexcited parabolic GaAsAl_xGa_1-xAs quantum wells. The spectra show sharp peaks corresponding to transitions between sublevels in the conduction band. The precision of the measurements allows a test of the simple harmonic oscillator model for the energy level structure. The energy gap and alloy composition of the Al_xGa_1-xAs layers are determined from resonance Raman scattering by optical phonons. We use these results to calculate the conduction band offset Q_e. We obtain Q_e ∼ 0.7, in agreement with recent experiments in square quantum wells.     

Raman scattering determination of folded acoustical phonon dispersion curves in large period GaAs/GaAlAs superlattices

We report the first experimental determination of the dispersion curves of folded acoustical modes in large period GaAs/Ga_1?xAl_xAs superlattices, obtained by scanning the incident wavelength in a Raman scattering experiment. Moreover, the resonant scattering evidences disorder activated Raman lines similar to those already reported in Ga_1?xAl_xAs single layers. These results imply the coexistence in Ga_1?xAl_xAs of dispersive virtual crystal acoustical modes with non dispersive disorder induced contributions. These features are explained on the basis of the Coherent Potential Approximation.     

Phonon-plasmon interaction in tunneling GaAs/AlAs superlattices

The phonon-plasmon interaction in tunneling GaAs _n /AlAs _m superlattices (m=5and 6≥n≥0.6 monolayers) was studied by Raman scattering spectroscopy. The interaction of optical phonons localized in GaAs and AlAs layers with quasi-three-dimensional plasmons strengthens as the thickness of GaAs quantum wells decreases and the electronic states in the superlattices become delocalized due to tunneling. It is assumed that the plasmons also interact with the TO-like phonon modes localized in quantum islands or in thin ruffled layers.     

1MeV Si+衬底加温注入Al0.3Ga0.7As/GaAs超晶格和GaAs的晶格损伤研究

用卢瑟福背散射／沟道技术研究了１ＭｅＶＳｉ⁺在衬底加温和室温下以不同剂量注入Ａｌ_0.3Ｇ_0.7Ａｓ／ＧａＡｓ超晶格和ＧａＡｓ后的晶格损伤。在衬底加温下，观察到Ａｌ_0.3Ｇａ_0.7Ａｓ／ＧａＡｓ超晶格和ＧａＡｓ都存在一个动态退火速率与缺陷产生速率相平衡的剂量范围，以及两种速率失去平衡的临界剂量。超晶格比ＧａＡｓ更难以损伤，并且它的两种速率失去平衡的临界剂量也大于ＧａＡｓ中的相应临界剂量，用热尖峰与碰撞模型解释了晶格损伤积累与注入剂量和衬底温度的关系。用ＣＮＤＯ／２量子化学方法计算了ＧａＡｓ和Ａｌ_xＧａ_1-xＡｓ中化学键的相对强度，并根据计算结果解释了注入过程中Ａｌ_0.3Ｇａ_0.7Ａｓ／ＧａＡｓ超晶格和ＧａＡｓ中晶格损伤程度的差别。 关键词：     

Resonant-Raman scattering from quasi-localized excitons in semiconductor quantum wells

Large polarization-dependent resonance enhancement is observed in first and second order Raman scattering in multiple quantum well $\text{GaAs}\text{(Al}{}_{\mathrm{x}}\text{Ga}{}_{\mathrm{1-x}}\text{)As}$ and $\text{GaAs}\text{AlAs}$ semiconductor heterostructures. Resonance enhancement is much stronger in the forbidden polarization than in the allowed and shows double resonance behaviour at incoming and outgoing photon energies. The resonance is stronger at incoming photon energies for one-phonon scattering and at outgoing photon energies for two-phonon scattering.     

Optical properties of AlxGa1-xAs/GaAs MQW studied by infrared ellipsometry and fourier transform infrared spectroscopy

The optical response of Al_xGa_1-xAs/GaAs MQW from near-infrared to far-infrared has been studied. Using infrared spectroscopic ellipsometry, we measured the optical response of the samples in the energy range 0.5-2.0eV, and oscillations have been observed. A multilayer film calculation indicates that this phenomenon results from interference. By Fourier transform infrared spectroscopy, the absorptance of double-well MQW has been measured in the energy range 0.08-0.25eV. The energy levels of subbands and the oscillator strengths were calculated from self-consistent interface potential theory. The calculation results are consistent with the measurements.     

Accumulation layer and interface effects in doped nonabrupt GaAs/AlxGa1-xAs heterojunctions

A theoretical model is proposed to describe doped nonabrupt GaAs/Al_xGa_1-xAs heterojunctions. It is used to study interface effects on the transmission properties and energy levels of electrons in these heterostructures. It is showed that interface effects are important in the case of high doping levels, and wide GaAs/Al_xGa_1-xAs interfaces.     

Spacer layer thickness fluctuation scattering in a modulation-doped AlxGa1-xAs/GaAs/AlxGa1-xAs quantum well

We theoretically study the influence of spacer layer thickness fluctuation（SLTF） on the mobility of a twodimensional electron gas（2DEG） in the modulation-doped Al x Ga 1 x As/GaAs/Al x Ga 1 x As quantum well.The dependence of the mobility limited by SLTF scattering on spacer layer thickness and donor density are obtained.The results show that SLTF scattering is an important scattering mechanism for the quantum well structure with a thick well layer.     

Impurity bands in Ga1-xAlxAs/GaAs quantum wells

We calculate the Density-of-States (DOS) for electrons bound to impurities in a thin sheet inside a Ga_1-xAl_xAs/GaAs quantum well. Impurities are considered at the center, midway to the interface and at the interface of the GaAs layer. It is shown that for reasonable impurity concentrations an impurity band appears separated from the lowest subband. The bandwidth is comparable with that obtained due to diagonal disorder assuming a uniform distribution inside the whole well.     

Barrier-disorder induced exciton relaxation via LO-phonons in GaAs/Al x Ga1−x As multiple quantum wells

Hot exciton relaxation is observed in GaAs/Al _x Ga_1–x As multiple quantum wells. The photolumnescence excitation spectra of the localized exciton emission at low temperatures and excitation densities are composed of narrow equidistant peaks exactly separated by the GaAs LO-phonon energy (36 meV). The relaxation mechanism via LO-phonons is found to be important for localized excitons in multiple quantum wells with GaAs layer thicknesses of about 50 Å, where pronounced alloy fluctuations in the barriers provide a strong additional lateral potential which suppresses the dissociation of hot excitons.     

MBE GaAs1-xSbx/GaAs应变层量子阱的光调制反射光谱

本文采用光调制反射光谱技术研究了MBE GaAs_1-xSb_x/GaAs应变层量子阱。通过实验分析和理论上对受应力作用后能带结构的估算,确认在这一系统中流体静压力作用引起的能带结构变化主要出现在导带上,同时也证实了GaAs_1-xSb_x/GaAs应变层量子阱属于第Ⅱ型量子阱结构。实验结果与理论估算符合很好。 关键词：     

Microscopic approach to the quantum size effect in superlattices

A new method for the microscopic calculation of electronic properties of superlattices is introduced and used to study the effects of carrier confinement in GaAs-Ga_1?xAl_xAs heterostructures. Our approach allows to evaluate the superlattice band structure and layer densities of states for arbitrary thickness of the GaAs and of the Ga_1?xAl_xAs slabs. We discuss the quantum size effect, the subband dispersion, the effective electron masses and the layer density of states near the conduction band edge for varying periodicity length and varying barrier thickness. Our results confirm simple potential well calculations and agree very good with experimental data.     

Tenseur de mobilite d'un super-reseau en presence de desordre d'interface

Mobility tensor, limited by island-like interface disorder, in type-I superlattices, is studied within a simple model (Kronig-Penney and plane waves). Computed results are presented, for GaAs-Ga_1?xAl_xAs superlattices, versus variations of temperature, superlattice period and defect parameters such as localisation, width and thickness. This interface scattering process has a significant influence on near equilibrium transport at low temperature.     

超晶格中GaAs/InGaAs界面与InGaAs/GaAs界面的特性差异

In_xGa_1-xAs缓冲层上生长In_yGa_1-yAs/GaAs超晶格（x＜y）．阱层处于压缩应变，垒层处于伸张应变，其厚度均小于Mathews-Blakeslee（M-B）平衡理论计算的临界厚度．透射电子显微镜及俄歇电子能谱、二级离子质谱测试发现，GaAs/In_yGa_1-yAs界面铟组分过渡区比In_yGa_1-yAs/GaAs界面铟组 关键词：     

Electron energy spectra in an elliptic quantum wire and elliptic nanotube

In the effective mass approximation, the electron spectra in an elliptic quantum wire and elliptic semiconductor nanotube are investigated. An exact electron energy spectrum in the GaAs elliptic quantum wire and elliptic semiconductor nanotube with impenetrable walls is obtained and an approximate solution of the Schrödinger equation is derived for a finite potential barrier height in the GaAs/Al _x Ga _1?x As elliptic quantum wire. It is demonstrated that the ellipticity of the quantum wire and nanotube results in removal of degeneration of the quasiparticle energy spectrum. Dependences of energies of even and odd states on the ratio of the ellipse semiaxes are nonmonotonic in character. In the limiting case of degeneration of elliptic quantum wires and nanotubes into circular ones, the quasi-particle energy spectrum coincides with the corresponding spectrum in cylindrical nanosystems.     

Transmission in symmetrical GaAs/AlxGa1-xAs double-barriers with compositionally nonabrupt interfaces

Transmission properties of electrons through GaAs/Al_xGa_1-xAs symmetrical double-barriers with abrupt and nonabrupt interfaces are calculated and compared. The interface potential and carrier effective-mass are obtained assuming a linear variation of the aluminium molar fraction in the transition regions GaAs ⇔ Al_xGa_1-xAs. When the electron energy E_0,-1,e is smaller than the double-barrier height V_x0 , changes in the internal interfaces widths shift tunneling resonances, while changes in the external interfaces increase the energy widths of the resonant transmission peaks. When E_0,-1,e > V_x0, both external and internal interfaces modify remarkably the transmission of nonabrupt GaAs/Al_xGa_1-xAs double-barriers when compared with the abrupt double-barrier, even if their widths are as small as two GaAs lattice parameters. However, the first transmission peaks of abrupt and nonabrupt GaAs/Al_xGa_1-xAs double-barriers are very similar, except when the interface widths are greater than four lattice parameters.     

Influence of exciton energy on intersubband transition of chirped superlattice GaAs/AlGaAs quantum cascade laser

The influence of exciton energy on intersubband transition was simulated for a chirped supperlattice quantum cascade laser of GaAs/Al_xGa_1-xAs. Exciton energy was modelled as a function of QW width for alloys of various percentages of constituent elements. The results showed that the exciton energy decreased proportionally with increasing QW width. Models were also generated to study exciton energy as a function of the percent alloy contents of Al_xGa_1-xAs barriers for QWs of various widths. Exciton energy showed characteristics of higher discrete energy when QW width was narrower. Transition energy was also simulated from e₁ and e₂ to the 1s exciton state as functions of applied electric field at various QW widths. Our simulation results showed that the transition energy from e₂ to the 1s exciton state increased proportionally to the increasing strength of the electric field. This transition energy was indicative of THz range radiation.     

稳定的GaAs (2 5 1 1)高密勒指数表面的电子结构

采用格林函数方法对具有稳定结构的GaAs(2 5 11)(1×1)表面的电子结构特性进行了计算. 结果表明：对于理想的GaAs(2 5 11)表面，基本带隙内的表面态主要处在三个能量区域，即 -0.1—0.1eV，085—10eV和1.4—1.6eV之间；吸附两个As原子形成(1×1)再构后，表面态的变化主要表现在0.85—1.0eV之间的表面态完全消失.结合电子数目规则，可以确定处在 - 0.1—0.1eV之间的表面态为全部填满的阴离子悬挂键态或再构引起的As As二聚体键的表 面态，而处在1.4— 关键词： 高密勒指数表面 电子结构 电子数目规则