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.     

宽带偏振不灵敏InGaAs半导体光放大器

采用压应变InGaAs量子阱和张应变InGaAs准体材料交替混合的有源结构，研制了宽带偏振不灵敏的半导体光放大器．此放大器在100～250mA的工作电流范围内，获得了大于70nm的3dB光带宽；在0～250mA工作电流和3dB光带宽波长范围内，偏振灵敏度小于1dB．对于1.55μm的信号光，在200mA的注入电流下获得了15.6dB的光纤到光纤的增益、小于0.7dB的偏振灵敏度和4.2dBm的饱和输出功率．     

ON THE METHOD OF ORTHOGONALITY CONDITIONS FOR SOLVING THE PROBLEM OF LARGE DEFLECTION OF CIRCULAR PLATE

In this paper,we reexamine the method of successive approximation presented byProf.Chien Wei-zang for solving the problem of large deflection of a circular plate,and findthat the method could be regarded as the method of strained parameters in the singularperturbation theory.In terms of the parameter representing the ratio of the centerdeflection to the thickness of the plate,we make the asymptotic expansions of thedeflection,membrane stress and the parameter of load as in Ref.[1],and then give theorthogonality conditions(i.e.the solvability conditions)for the resulting equations,bywhich the stiffness characteristics of the plate could be determined.It is pointed out thatwith the solutions for the small deflection problem of the circular plate and theorthogonality conditions,we can derive the third order approximate relations between theparameter of load and the center deflection and the first-term approximation of membranestresses at the center and edge of the plate without solving the differential equ