二元超晶格弹性应力的能带理论计算

根据量子能带理论 ,采用经验赝势方法 ,对 (Pb) n/ (Bi) n,(Al) n/ (As) n 的假想简立方二元超晶格结构的弹性应力进行了计算 .结果表明弹性应力随超晶格周期λ的增加而迅速升高至一定大小后趋于稳定 ,且只有在周期较小时才同过渡金属氮化物超晶格硬度随周期的变化的趋势定性一致 ,为超晶格硬度随周期的变化提供了一种可能的解释     

Magnetoluminescence properties of Hg1−xCdxTe epitaxial layers and superlattice structures grown by metalorganic molecular beam epitaxy

We present a study of the electro-optical properties ofHg _1- xCd_xTe epitaxial layers and Hg_1-x Cd_xTe/CdTe (0.28 < x < 0.30) superlattice structures by x-ray diffraction, lateral transport and photo- and magneto-luminescence measurements. Systematic studies of the excitation intensity and magnetic field dependence of the photoluminescence revealed direct evidence of an excitonic contribution to the observed luminescence in Hg_{1- x}Cd_xTe epitaxial layers. Similar investigations of the superlattice structures indicated that excitonic corrections were required to adequately fit the luminescence data. Optical gains of 80 cm⁻¹ were obtained for an excitation intensity of 100 kW/cm² indicating suitable electro-optical properties for making efficient mid-infrared laser diodes.     

Far-infrared detector based on HgTe/HgCdTe superlattices

HgTe/Hg_0.05Cd_0.95Te superlattices (SLs) were grown on (112)B oriented Cd_0.96Zn_0.04 Te substrates using molecular beam epitaxy (MBE). The SLs, consisting of 100 periods of 80-Å-thick HgTe wells alternating with 77-Å-thick Hg_0.05Cd_0.95Te barriers, were designed to operate as detectors in the far-infrared (FIR) region. Infrared absorption spectroscopy, high-resolution transmission electron microscopy (TEM), Hall effect measurements, and x-ray diffraction were used to characterize the superlattice layers. A series of annealing experiments were initiated to quantify the temperature-dependent interdiffusion of the HgTe wells and Hg_0.05Cd_0.95Te barriers and consequently their degradation, which shifts the absorption edges of the SLs to higher energies, since a high-temperature ex situ anneal is normally required in order to produce the p-type material required for a photovoltaic detector. Results from infrared absorption spectroscopy, TEM, and Hall effect measurements for the annealed samples are presented. A FIR SLs single-element photoconductive (PC) device was designed and fabricated. Both material characterization and device testing have established the applicability of the HgTe/Hg_0.05Cd_0.95Te SLs for the FIR region.     

Critical thickness of GaAs/InGaAs and AlGaAs/GaAsP strained quantum wells grown by organometallic chemical vapor deposition

In this paper we describe a study of strained quantum wells (QWs) as a means to experimentally observe the critical thickness (h _c) for the formation of interfacial misfit dislocations. Two material systems were investigated: GaAs/In_0.11Ga_0.89As, in which the QW layers are under biaxialcompression, and Al_0.35Ga_0.65As/GaAs_0.82P_0.18, in which the QW layers are under biaxialtension. Samples were grown by atmospheric pressure organometallic chemical vapor deposition, and characterized by low-temperature photoluminescence (PL), x-ray diffraction, optical microscopy, and Hall measurements. For both material systems, the observed onset of dislocation formation agrees well with the force-balance model assuming a double-kink mechanism. However, overall results indicate that the relaxation is inhomogeneous. Annealing at 800–850° C had no significant effect on the PL spectra, signifying that even layers that have exceededh _c and have undergone partial relaxation are thermodynamically stable against further dislocation propagation.     

电场中三层铁电超晶格的物理性质研究

基于微分算符技术的相关有效场理论研究用伊辛模型描述的铁电三层超晶格的物理性质。讨论了电场对电极矩、电极化率、热电系数等物理性质的影响。     

Growth of GaAs1−xPx/GaAs and InAsxP1−x/InP strained quantum wells for optoelectronic devices by gas-source molecular beam epitaxy

In this paper we show that pseudomorphically strained heterostructures of InAs _x P_1−x /InP may be an alternative to lattice-matched heterostructures of In_1−x Ga _x As _y P_1−y /InP for optoelectronic applications. We first studied the group-V composition control in the gas-source molecular beam epitaxy (GSMBE) of the GaAs_1-x P _x /GaAs system. Then we studied GSMBE of strained InAs _x P_1−x /InP multiple quantum wells with the ternary well layer in the composition range 0.15 <x < 0.75. Structural and optical properties were characterized by high-resolution x-ray rocking curves, transmission electron microscopy, absorption and low-temperature photoluminescence measurements. High-quality multiple-quantum-well structures were obtained even for highly strained (up to 2.5%) samples. The achievement of sharp excitonic absorptions at 1.06, 1.3 and 1.55μm at room temperature from InAs _x P_1−x /InP quantum wells suggests the possibility of long-wavelength optoelectronic applications.     

Convergent-beam electron diffraction of CaZr4O9, a complex zirconia alloy phase

The point-group and space-group symmetry of the controversial fluorite-based stoichiometric superlath phase of ø₁ (CaZr₄O₉: Z=16), considered to be a coherently-intergrown subphase of lime-stabilized zirconia, is examined. Using convergent-beam and selected-area electron diffraction, it is determined that the space group of ø₁ is C2/c, in apparent agreement with earlier studies utilizing other diffraction techniques.     

Structures of an asymmetrically coupled double-well superlattice by double-crystal X-ray diffraction

An asymmetrically coupled (GaAs/AlAs/GaAs/AlAs)/GaAs (001) double-well supperlattice is studied by HRDCD (high resolution double-crystal X-ray diffractometry). The intensity of satellite peaks is modulated by wave packet of different sublayers. In the course of simulation, the satellite peaks in the vicinity of the node points of wave packet are very informative for precise determination of sublayer thickness and for improving accuracy.