Acoustoelectric measurements of minority and majority carrier mobilities in semiconductors including Hg1−x Cd x Te

Acoustoelectric voltages versus absorbed surface acoustic wave (SAW) power measurements are used to nondestructively determine carrier mobilities in bulk silicon, GaAs and epitaxial Hg_1−x Cd _x Te employing a separate medium convolver structure. The longitudinal component of the acoustoelectric signals (LAV) has been used in the past to determine the carrier mobilities in semiconductor films. In the present work, it is shown that the transverse component of the acoustoelectric signals (TAV) can also be used to measure the carrier mobilities. TAV and LAV measurements yield mobilities in perpendicular directions. Hence, these measurements can be used to study the electron mobilities of a two-dimensional electron system in superlattices. A new delay line structure is introduced to invert the semiconductor surface through the field effect to measure the minority carrier mobilities. Carrier mobilities in graded epitaxial Hg_1−x Cd _x Te are measured after subsequent etching of the surface to obtain the mobility values versus depth. The findings of the above measurements and Hall measurements are in satisfactory agreement. Partially supported by Night Vision Lab, through Contract No. DAAG 29-81-D-0100     

半导体超晶格声子激光器的研究进展

太赫兹频率的相干声子在纳米尺度器件的探测和操控领域具有重要的应用价值。半导体超晶格声子激光器是实现太赫兹频率相干声子源稳定输出的重要途径。本文首先回顾了GHz到THz频率范围声学放大的多种方法,然后详细阐述了超晶格声子放大、超晶格声学布拉格镜的工作原理与设计方法以及声子激光器的阈值条件,同时总结了电抽运和光抽运结构器件的研究现状,最后简要讨论了亚太赫兹声子激光器在声-电子领域的应用。分析表明,这种能够产生强相干太赫兹声子的半导体超晶格声子激光器在纳米尺度器件的探测与成像等方面具有广阔的发展前景。     

Enhancement of the nonlinear acoustoelectric interaction in a photoexcited plasma in a quantum well

Nonlinear interaction of an intense surface acoustic wave (SAW) with a 2D electron-hole plasma generated by light in a semiconductor quantum well near a piezoelectric crystal is investigated. It is shown that, in a strongly nonlinear regime, the acoustoelectric interaction is enhanced because of the accumulation of carriers in the field of an intense SAW. In addition, in a strongly nonlinear regime, the dissipation of the acoustic wave energy increases and the sound velocity decreases. These dependences fundamentally differ from those observed in a unipolar plasma. For high sound intensities, analytical results are obtained.     

MBE[(GaAs)l(Ga1-λAlxAs)m]n/GaAS(001)一维超晶格的X射线双晶衍射测量

本文着重介绍了MBE[(GaAs)l(Ga1-xAlxAs)m]n/GaAs(001)一维超晶格的X射线双晶衍射测量方法。根据卫星峰的出现,证明超晶格的存在。基于超晶格的台阶模型和X射线衍射的运动学理论,推导出超晶格多结构参数的计算方法。并对X射线双晶给出的其他信息做了必要的讨论。     

The acoustic method of the surface potential investigation in GaP:Te (110) real surface

The acoustic method of the surface potential investigation in semiconductors has been described. The method is based on the transverse acoustoelectric effect TAV in layered structure: piezoelectric waveguide – semiconductor. The paper presents experimental results of the surface potential investigations obtained after various surface treatments in the GaP:Te (110) single crystals. Strong impact of mechanical and chemical surface treatments upon the surface potential values are observed. It follows from the measurements that the acoustic method may give interesting information about the surface potential of the semiconductor monocrystals in the high frequency range.     

半导体中的输运过程

半导体的输运性质直接决定了半导体器件的性能，如响应时间、截止频率等，因此与半导体器件发展的同时，人们对半导体的输运性质进行了广泛的实验和理论研究。文章根据半导体物理的发展历史，分体半导体输运、调制掺杂异质结输运、超晶格微带输运、弹道输运以及介质系统输运等几个方面来讨论这一问题。     

Transverse acoustoelectric voltage inversion and its application to semiconductor surface study: CdS

The transverse acoustoelectric voltage inversion has been observed in CdS. It is found to be due to the inversion of the semiconductor surface. The inversion layer results from a high magnitude of the dc transverse acoustoelectric voltage developed on the semiconductor surface. The acoustoelectric voltage inversion is strongly dependent on the wavelength and intensity of light illuminating the semiconductor surface, and the power input of the SAW. The sub bandgap spectral response of the transverse acoustoelectric voltage determines the positions of the surface states in the energy gap. The above bandgap spectrum determines the photon energy in which transition from bulk to surface absorption takes place and the photon energy for complete surface absorption.     

Observation of acoustically induced space charge gratings in CdS

Static space charge gratings, produced via a nonlinear acoustoelectric interaction, have been directly observed in CdS by means of laser diffraction. Spatial and temporal filtering techniques were used to separate the required optical information from extraneous signals due to background and acoustic diffraction effects.     

半导体微结构物理效应及其应用讲座第三讲半导体的激子效应及其在光电子器件中的应用

人们对半导体中的电子空穴对在库仑互作用下形成的激子态及其有关的物理性质进行了深入研究.激子效应对半导体中的光吸收、发光、激射和光学非线性作用等物理过程具有重要影响,并在半导体光电子器件的研究和开发中得到了重要的应用.与半导体体材料相比,在量子化的低维电子结构中,激子的束缚能要大得多,激子效应增强,而且在较高温度或在电场作用下更稳定.这对制作利用激子效应的光电子器件非常有利.近年来量子阱、量子点等低维结构研究获得飞速的进展,已大大促进了激子效应在新型半导体光源和半导体非线性光电子器件领域的应用.     

A microscopic model of sequential resonant tunneling transport through weakly coupled superlattices

A microscopic model is developed for resonant tunneling transport in weakly coupled semiconductor superlattices in a constant external electric field. The model takes into account multiple subbands and electric-field dependence of scattering by acoustic and optical phonons, charged impurities, and interface roughness. The model is used as a basis for computing the resonant-tunneling profiles for structures with small size-quantization energies. The computed results are in good agreement with experiment. In structures of this type, an important role is played by electric-field dependence of scattering processes and the threshold behavior of elastic processes is strongly manifested. A substantial asymmetry is predicted not only for the first tunneling resonance, but also for higher order resonant tunneling processes.     

Effect of conduction electrons on interaction of ultrasound with Mössbauer gamma rays in piezoelectri ic semiconductors

The interaction of Mössbauer gamma rays with acoustic waves generated in the thin platelet of Fe⁵⁷ doped A²B⁶ group piezoelectric semiconductor is studied as a function of crystal conductivity. It is shown that the intensity of the unshifted resonant absorption line in some case is very sensitive to the value of conductivity and thus could be utilized as a probe for acoustoelectric bulk effects.     

半导体纳米材料和物理

半导体纳米材料是纳米材料的一个重要组成部分，纳米结构的电子和光子器件将成为下一代微电子和光电子器件的核心。文章介绍了半导体纳米材料研究的新进展，包括四个方面：半导体自组织生长量子点，纳米晶体，微腔光子晶体和纳米结构中的自旋电子学。本世纪开始的半导体纳米材料的研究是上世纪半导体超晶格量子阱研究的延续，同时又开辟了一些新的领域，如：单电子的电子学、单光子的光子学，微腔和光子晶体，稀磁半导体和自旋电子的相干输运等，这些研究将为研制在新原理基础上的新器件和实现量子计算、量子通信打下基础。     

Quantization accuracy of the acoustoelectric current

By deriving analytical formulae for the quantization accuracy of the acoustoelectric current, we reveal that: (1) the flatness of the current plateau for the typical present devices has reached the theoretical limit of about 100 ppm over a 1/1000 change of the gate voltage; (2) increasing the transport channel length, and counterintuitively, increasing the acoustic wavelength as well, would improve the quantization accuracy, and very promisingly up to 0.01 ppm as required for a quantum current standard.     

Direct and interwell excitons in magnetic nanostructures

The energies of direct and interwell excitons in superlattices based on europium and lead sulfides have been calculated. It is established that these excitons have higher oscillator strengths and binding energies due to the indirect exchange. This circumstance can be used in semiconductor devices operating on exciton transitions.     

Dielectric superlattices for nonlinear optical effects

Dielectric superlattices show a lot of new phenomena that are promising in applications, such as nonlinear optical frequency conversion and optical bistability. This paper reviews the main achievements in this field. Much has been focused on the work done in our Lab. Since 1980, we have extended the concept of superlattice from semiconductor to dielectrics. When quasi-phase-matching technique is introduced into a quasiperiodic dielectric superlattice, more interesting phenomena can occur. For example, multiwavelength second-harmonic generation and coupled parametric processes such as direct third-harmonic generation have been realized with high efficiency. A new mechanism for optical bistability in a 2-dimensional dielectric superlattice, i.e. a 2-dimensional nonlinear photonic crystal, has been proposed theoretically had proved experimentally.     

Monte Carlo Simulation of THz-Pulse Generation from Bulk GaAs Surface

An ensemble Monte Carlo simulation method has been used to study THz-pulse generation from semiconductor GaAs surface excited by a femtosecond laser pulse and biased in high electrical field near 100kV/cm. Electron transport is simulated using the three-valley conduction band model and taking into account acoustic, optical (polar and nonpolar) and intervalley phonon scattering mechanisms. Our simulations show that the THz temporal waveforms have a close relationship with the biased external field and the THz radiation is saturated with the increase of the biased field, these findings have not been exploited by the existing theoretical analyses. Power spectra show that the higher biased electrical field benefits the frequency extension for the THz radiation.     

太赫兹场和倾斜磁场对超晶格电子动力学特性调控规律研究

微带超晶格在磁场和太赫兹场调控下表现出丰富而复杂的动力学行为, 研究微带电子在外场作用下的输运性质对于太赫兹器件设计与研制具有重要意义. 本文采用准经典的运动方程描述了超晶格微带电子在沿超晶格生长方向(z方向)的THz场和相对于z轴倾斜的磁场共同作用下的非线性动力学特性. 研究表明, 在太赫兹场和倾斜磁场共同作用下, 超晶格微带电子随时间的演化表现出周期和混沌等新奇的运动状态. 采用庞加莱分支图详细研究了微带电子在磁场和太赫兹场调控下的运动规律, 给出了电子运行于周期和混沌运动状态的参数区间. 在电场和磁场作用下, 微带电子将产生布洛赫振荡和回旋振荡, 形成复杂的协同耦合振荡. 太赫兹场与这些协同振荡模式之间的相互作用是导致电子表现出周期态、混沌态以及倍周期分叉等现象的主要原因.     

Molecular tuning of quantum Hall edge states

Hybrid organic/inorganic devices may find applications as sensors and in futuristic molecular-electronic devices. Here, we demonstrate molecular control of vertical transport in semiconductor superlattices in strong magnetic fields by adsorption of organic molecules onto the sidewalls of a GaAs/AlGaAs device. The molecules have identical attachment groups functionalized by end groups with different electronegativities. For magnetic fields in quantized Hall states, we find that the adsorbate substantially modifies the network of edge states that carries the electrical current. The data indicate that molecules with appropriately chosen end groups can enhance or decrease the vertical conductivity of the edge state system.     

Ultrafast carrier dynamics in semiconductor nanostructures: interplay between coherence and relaxation

The strong coupling between coherent and incoherent ultrafast phenomena in the electro-optical response of semiconductor nanostructures is discussed theoretically within a density matrix formalism. In particular, the problem of scattering-induced damping of Bloch oscillations in superlattices is reviewed. Moreover, a generalization to ‘open systems’ of the conventional semiconductor Bloch equations is discussed. The presence of spatial boundary conditions manifests itself through self-energy corrections and additional source terms in the kinetic equations. As an example, some simulated experiments of quantum transport phenomena through double-barrier structures are reviewed.     

近周期超晶格中的声学声子及其光散射特性

利用转移矩阵方法计算了近周期超晶格体系（包括有限周期数的超晶格、耦合超晶格、层厚起伏和层厚渐变的超晶格）中声学声子的喇曼散射谱．结果表明上述近周期超晶格的光散射特性与理想严格周期的体系和完全无序的体系都不相同，呈现出许多独特的性质．对有限周期数的超晶格，由于边界的存在，喇曼谱中除了理想超晶格中存在的折叠声学声子峰（主峰）外，还会出现一系列等间距分布的卫星峰．对耦合超晶格体系，理想超晶格中存在的主峰将出现分裂．对层厚起伏变化的超晶格，主峰呈现非对称展宽，展宽主要出现在高波数端．计算结果和实验测得的谱线作了比 关键词：