Structural Control of Rashba Spin–Orbit Coupling in In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As Quantum Wells

We investigated the correlation between the Rashba spin–orbit coefficient α and potential shape of the quantum wells (QW), where α values are experimentally deduced from the weak antilocalization analysis. We studied the gate I–V properties of the QW samples and have obtained results consistent with the potential shapes predicted for these QWs.     

Photoluminescence of heterostructures with highly strained GaAs quantum wells in Al0.48In0.52As and Ga0.47In0.53As layers

Heterostructures comprising highly strained GaAs quantum wells in Al_0.48In_0.52As and Ga_0.47In_0.53As layers have been grown by the metalorganic chemical vapor deposition method on InP(100) substrates. The photoluminescence spectra of these structures have been studied, and it is established that GaAs quantum wells form type-I heterojunctions with Al_0.48In_0.52As layers and type-II heterojunctions with Ga_0.47In_0.53As layers.     

Influence of surface scattering on the anomalous conductance plateaus in an asymmetrically biased InAs/In(0.52)Al(0.48)As quantum point contact

We study of the appearance and evolution of several anomalous (i.e., G < G(0) D 2e(2)/h) conductance plateaus in an In(0.52)Al(0.48)As/InAs quantum point contact (QPC). This work was performed at T = 4:2 K as a function of the offset bias ΔV(G) between the two in-plane gates of the QPC. The number and location of the anomalous conductance plateaus strongly depend on the polarity of the offset bias. The anomalous plateaus appear only over an intermediate range of offset bias of several volts. They are quite robust, being observed over a maximum range of nearly 1 V for the common sweep voltage applied to the two gates. These results are interpreted as evidence for the sensitivity of the QPC spin polarization to defects (surface roughness and impurity (dangling bond) scattering) generated during the etching process that forms the QPC side walls. This assertion is supported by non-equilibrium Green function simulations of the conductance of a single QPC in the presence of dangling bonds on its walls. Our simulations show that a spin conductance polarization as high as 98% can be achieved despite the presence of dangling bonds. The maximum in is not necessarily reached where the conductance of the channel is equal to 0:5G(0).     

Surface morphology of ErP layers on InP and Ga0.52In0.48P

We have grown ErP on Ga_0.52In_0.48P (001) lattice-matched to GaAs and on InP (001) by low-pressure organometallic vapor phase epitaxy and investigated the surface morphology of ErP layers. Lattice-mismatch in ErP/Ga_0.52In_0.48P/GaAs heterostructures (Δa / a = − 0.8%) is much less than that of ErP/InP heterostructures (− 4.5%). Extended X-ray absorption fine structure measurement revealed that Er exists in the form of ErP rock-salt structure in both samples. The estimated growth rate of ErP on Ga_0.52In_0.48P is 1.8 ML/h. Our results demonstrate that ErP on Ga_0.52In_0.48P has smaller surface roughness than ErP on InP. Moreover, an ErP layer exists underneath the surface about 2 ML and the surface roughness does not depend on the ErP thickness in the range of our experiments (2.2–13.7 ML).     

Optical and Structural Properties of In_(0.52)Al_(0.48)As/InP Structures Grown at Very High Arsenic Overpressures by Molecular Beam Epitaxy

Growth of ln0.52Al0.48As epitaxial layers on lnP(100) substrates by molecular beam epitaxy at a wide range of arsenic overpressures (V/III flux ratios from 30 to 300) has been carried out. Analysis performed using low-temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) shows a strong and prominent dependence of the PL and XRD linewidths on the V/III flux ratio. Under our growth conditions, both the PL and XRD linewidths exhibit a minimum point at a V/III flux ratio of 150 which corresponds to a maximum in the PL intensity and XRD intensity ratio. Flux ratios exceeding 150 result in an increase in both the PL and XRD linewidths corresponding to a reduction in their associated intensities. Room temperature Raman scattering measurements show a narrowing in the lnAs-like and AlAs-like longitudinal-optic (LO)phonon linewidths which broaden at high flux ratios, while the LO phonon frequencies exhibit a gradual reduction as the flux ratio is increased. PL spectra taken at increasing temperatures show a quenching of the main emission peak followed by the evolution of a broad lower energy emission which is possibly associated with deep lying centres. This effect is more prominent in samples grown at lower V/III flux ratios. Hall effect measurements show a gradual reduction in the mobility in correspondence to an increase in the electron concentration as the flux ratio is increased.     

Anisotropic distribution of crystalline defects along [011] and [011] directions in In0.52AI0.48As buffer layers grown on InP

Abstract

Layers of In_0.48Al_0.52As grown by molecular beam epitaxy (MBE) on InP (100) substrates have been examined by transmission electron microscopy (TEM). At a low growth temperature (Tg=300°C) a <disp-formula><graphic href="splitsection1-m2.tif"/></disp-formula> microtwinned structure was observed, the origin of which has been explained taking into account the limited kinetics of group III atoms and the differences in the propagation speed of the surface steps during MBE growth. For growth temperatures in the range 440–530°C, the defect densities decrease monotonically; threading dislocations and stacking faults on the <disp-formula><graphic href="splitsection1-m2.tif"/></disp-formula> and <disp-formula><graphic href="splitsection1-m3.tif"/></disp-formula> planes are the prevailing types of defect. The asymmetry of fault densities between the <disp-formula><graphic href="splitsection1-m2.tif"/></disp-formula> and <disp-formula><graphic href="splitsection1-m4.tif"/></disp-formula> planes has been discussed on the basis of the different mobilities of the partial dislocations bordering the faults.     

Characterization of In0.48Ga0.52P-based thin-layer structures using spectroscopic ellipsometry

Spectroscopic ellipsometry (SE), a non-destructive optical method, was used for the characterization of In_0.48Ga_0.52P-based thin-layer structures. Two types of sample structures were investigated. One was an In_0.48Ga_0.52P-based single-layer structure and the other was an In_0.48Ga_0.52P-based multi-layer structure. Our objective was to determine the optical properties of In_0.48Ga_0.52P for the single-layer samples and to characterize the structures of the multi-layer samples, such as layer thicknesses. For each sample investigated, the measured spectra were analyzed with an appropriate fitting model, which was constructed based on the sample's nominal structure. In the determination of the optical properties of In_0.48Ga_0.52P, two methods were employed, namely, the harmonic oscillator approximation and the wavelength-by-wavelength fitting method, which is routinely used in SE analysis. The advantages and disadvantages of these two methods are discussed with the results from the chosen samples. In the structural characterization, the thickness results obtained by SE were compared with the corresponding ones determined by cross-sectional transmission electron microscopy. It is shown that, for each sample under study, very good agreement was found between the results obtained by the two methods. This in turn demonstrates that SE is reliable for thickness characterization of the multi-layer samples.     

Temperature dependent model dielectric function of highly disordered Ga0.52In0.48P

We report on the temperature dependence of the dielectric function of Ga_0.52In_0.48P from room temperature to 500°C, and for photon energies from 0.75 eV to 5 eV. The undoped, highly disordered Ga_0.52In_0.48P thin film was grown by metal-organic vapor phase epitaxy lattice matched onto a (001) GaAs substrate. The dielectric function of Ga_0.52In_0.48P was measured by in-situ spectroscopic ellipsometry, and analyzed using Adachi's composite critical point model. We provide a second-order temperature expansion parameter set for calculation of the Ga_0.52In_0.48P dielectric function and its temperature dependence, and which may become useful for in situ growth control or optoelectronic device performance evaluation at elevated temperatures. We discuss the temperature-induced shift of critical point transition energy parameters.     

Tunneling Density of States of Indium Oxide Films Through the Superconductor to Insulator Transition

We present planar tunneling junction spectroscopy measurements on disordered amorphous indium oxide films on both sides of the superconductor–insulator transition. Our measurements directly reveal a superconducting gap in the insulating phase. The measured energy gap has the same energy scale on both sides of the transition. Unlike the case of granular films, the tunneling curves cannot be fitted to the BCS density of state expression, even when introducing a broadening parameter to account for nonthermal broadening sources. The results are consistent with the presence of superconducting islands of which superconducting properties depend on film disorder and on the carrier density of the superconducting material.     

SiCp/Al-Si复合材料中SiC/Al界面处亚晶铝带的研究

通过利用ＴＥＭ研究ＳｉＣｐ／Ａｌ－Ｓｉ昨合材料发现,ＳｉＣ／Ａｌ界面结合紧密,在靠近ＳｉＣ界面的Ａｌａ基体中,有一层厚度小于１μｍ的“亚晶铝带”,它紧靠ＳｉＣ表面形成,与远离ＳｉＣ的Ａｌ基体有几度的位向差,这种“亚晶铝带”在ＳｉＣ／Ａｌ界面上普遍存在,其内有大量位错。     

SiC_p/Al-Si复合材料中SiC/Al界面处亚晶铝带的研究

通过利用 TEM研究 Si Cp/ Al- Si复合材料发现 :Si C/ Al界面结合紧密 ,在靠近 Si C界面的 Al基体中 ,有一层厚度小于 1μm的“亚晶铝带”,它紧靠 Si C表面形成 ,与远离 Si C的 Al基体有几度的位向差 ;这种“亚晶铝带”在 Si C/ Al界面上普遍存在 ,其内有大量位错。     

Observation of e2/h Conductance Steps in a Side-Gate Point Contact on In0.75Ga0.25As/In0.75Al0.25As Heterostructure

In 1996, it was suggested by K. J. Thomas et al. (Phys. Rev. Lett. 77, 135 (1996)) that 0.7(2e²/h) conductance structure in Quasi-1DEG (Q1DEG) at GaAs/AlGaAs heterostructure might be related to spin polarization at zero magnetic field. We have recently studied spontaneous spin-splitting in the 2DEGs formed at normal metamorphic In_0.75Ga_0.25As/In_0.75Al_0.25As heterojunctions grown on GaAs substrates and obtained the value of ?10 meV as the zero-field splitting at Fermi level (Y. Sato et al., J. Appl. Phys. 89, 8017 (2001)). In this work, we attempted to observe spin-related phenomena in this heterojunction Q1DEGs at zero magnetic field. We observed e²/h conductance steps in low electron concentration side-gate point contact.     

Application of selective implantation in Al0.5Ga0.5As/In0.25Ga0.75As/GaAs pseudomorphic single quantum wire structures

A pseudomorphic Al0.5Ga0.5As/In0.25Ga0.75As/GaAs asymmetric quantum wire (QWR) structure was grown on GaAs V-grooved substrate by low pressure metal organic vapor phase epitaxy. The formation of crescent shaped QWRs at the bottom of the V-grooves was confirmed by both transmission electron microscopy and photoluminescence (PL) spectra. The temperature dependence of PL spectra demonstrated a fast decrease of the sidewall quantum well PL intensity with increasing temperature, which originates from relaxation of carriers from well to wire region. The self-aligned dual implantation technique was successfully used to selectively disable the adjacent quantum structures. Decrease of the PL intensity of QWR at 8 K was observed after selective implantation, which resulted from a decreased number of carriers relaxed from adjacent quantum structures.     

Positive delayed photoconductivity in double heterostructures Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As of the p-type

Positive delayed photoconductivity was observed for the first time in double p-type heterostructures Al_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5 As upon exposure to the radiation of a red light-emitting diode. In this state, the concentration and mobility of two-dimensional holes are increased 1.5 and 1.7 times, respectively, as compared to the initial dark values. The delayed photoconductivity can be explained by the presence of deep electron traps located above the Fermi level at the inverted heterointerface.     

激光脉冲外延生长Pb(Zr0.52Ti0.48)O3薄膜及其特性研究

利用激光脉冲法在LaAlO3衬底上沉积制备LaNiO3薄膜作为底电极并外延生长(100) Pb(Zr0.52Ti0.48)O3铁电薄膜,系统研究了生长温度对PZT外延结构和电学特性的影响.研究发现当生长温度高于550℃时即可得到外延(100)PZT薄膜.在对所制备的PZT薄膜的结构和性能测试表明,650℃下生长的PZT薄膜外延性最佳,并且表现出优异的介电和铁电性能,介电常数ε、剩余极化Pr和矫顽场Ec分别为900、26.5 μC/cm2和52.1kV/cm.试验还证实这种外延PZT薄膜具有优良的抗疲劳特性,可用于铁电存储器的制备中去.     

Al0.15Ga0.85As／GaAs与In0.15Ga0.85As／GaAs甚长波QWIPs响应率的仿真对比

对In0.15Ga0.85As／GaAs和Al0.15Ga0.85As／GaAs两种甚长波段量子阱红外探测器（QwIP）响应率进行计算。采用物理模型与等效电路模型，结合Crosslight和Spice等软件详细表征了这两种QWIPs的吸收系数、暗电流、响应率、量子效率等物理特性。结果表明随外加偏压的升高QWIP的响应率增加，T=40K时，In0.15Ga0.85As／GaAs QwIP的响应率明显比Al0.15Ga0.85As／GaAs QWIP高出2倍以上，通过对量子效率的对比，使仿真结果得到验证。     

Low thermal drift in highly sensitive doped channel Al0.3Ga0.7As/GaAs/In0.2Ga0.8As micro-Hall element

Micro-Hall sensors with high sensitivity, low noise, and high thermal stability, 5 μm square, are fabricated using pseudomorphic Al_0.3Ga_0.7As/GaAs/In _y Ga_1-y As (0.2 ≤ y ≤ 0.3) heterostructures with Si-doped channels. The structures were optimized for thermal stability using a calculation of the self-consistent solution of Schrödinger-Poisson equations and Fermi-Dirac statistics in Hartree approximation. The optimized structure based on a Si-δ-doped 144 Å In_0.2Ga_0.8As quantum well embedded into uniformly doped GaAs channel showed thermal drifts of only 90 ppm·K^?1 in current drive mode and 192 ppm K^?1 in voltage drive mode. The measurements of the absolute magnetic sensitivity and the low frequency noise were done. The micro-Hall sensor, optimized for thermal drift, is able to resolve the magnetic field of 438 nT.