Compound semiconductor MOSFETs

Enhancement mode, high electron mobility MOSFET devices have been fabricated using an oxide high-κ gate dielectric stack developed using molecular beam epitaxy. A template layer of Ga₂O₃, initially deposited on the surface of the III-V device unpins the GaAs Fermi level while a (Gd_xGa_1−x)₂O₃ bulk ternary layer forms the highly resistive layer to reduce leakage current through the dielectric stack. A midgap interface state density of ∼2 × 10¹¹ cm⁻² eV⁻¹ and a dielectric constant of 20 are determined using electrical measurements.. N-channel MOSFETs with a gate length of 1 μm and a source-drain spacing of 3 μm show a threshold voltage, saturation current and transconductance of 0.11 V, 380 mA/mm and 250 mS/mm, respectively.     

On the term “activation energy” in accelerated lifetime tests of plastic encapsulated semiconductor components

It is shown that the energy characterizing the temperature dependence of chemical reaction rates and of component failure rates at constant relative humidity is not an activation energy. A thorough contemplation of the behaviour of electrolytic corrosion leads to the conclusion that an application of Arrhenius' law to this type of failure mechanism without any reservations is not allowed.     

Exciton binding energy in semiconductor quantum dots

In the adiabatic approximation in the context of the modified effective mass approach, in which the reduced exciton effective mass μ = μ(a) is a function of the radius a of the semiconductor quantum dot, an expression for the exciton binding energy E _ex(a) in the quantum dot is derived. It is found that, in the CdSe and CdS quantum dots with the radii a comparable to the Bohr exciton radii a _ex, the exciton binding energy E _ex(a) is substantially (respectively, 7.4 and 4.5 times) higher than the exciton binding energy in the CdSe and CdS single crystals.     

Compound semiconductor equipment manufacturers perform well in VLSI survey

Compound semiconductor equipment manufacturers are well represented in this year’s VLSI customer satisfaction survey. Conducted annually, the survey looks at equipment performance and customer service, and asks semiconductor manufacturing equipment users to rank suppliers on a 10 point scale. Equipment performance is measured in terms of: build quality, cost of ownership, uptime, software, usable throughput, quality of results, and product performance. For customer service, the measures are: process support, field engineering support, spares support, support after sales, technical leadership in the supplier’s field and the supplier’s overall commitment to supporting its customers’ needs.This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news.     

Compound semiconductor research at the University of Washington in Seattle,Washington

The electronic materials program at the University of Washington is a research collaboration involving three departments: Chemical Engineering, Electrical Engineering, and Materials Science and Engineering. The program addresses current important issues in three areas: superlattices and artificially structured materials, epitaxial deposition of electronic materials on dissimilar substrates, and use of surface chemistry and atomic layer growth to achieve epitaxial deposition at reduced temperatures. A key enabling technology for these research areas is the development and use of non-invasive process monitoring and real-time control. Research in these areas is leading to new concepts in materials processing and epitaxial growth technologies for the semiconductor industry.     

界面效应对半导体量子点异质结的电子能级扰动的分析

提出采用壳状结构和渐变有限深势阱模型的方法来分析界面效应对半导体量子点异质结的束缚态电子能级的扰动。模拟计算表明，对于处于强受限的量子点，界面效应明显。随着量子点的表面区域增大和量子点尺寸的减小，能级移动增加，在低能级时近似呈线性变化关系。     

Threshold energy effect on avalanche breakdown voltage in semiconductor junctions

The band bending for avalanche breakdown in semiconductor junctions and its temperature dependence are predicted taking account of threshold energy effects on the ionization process in semiconductors. Where experimental results exist, the theoretical predictions and experimental results are in excellent agreement. In the high electric field region inclusion of both bulk and boundary threshold energy effects is essential. The predictions were based on exact solutions in the nonlocalized ionization coefficient formulation developed by Okuto and Crowell who showed that ionization coefficients as usually understood are functions of both electric field and position in a device. Predictions for abrupt and p-i-n junctions in Ge, Si, GaAs and GaP are presented.     

半导体极性膜中束缚磁极化子的自陷能

采用线性组合算符法和幺正变换方法,研究极性晶体膜中束缚磁极化子的自陷能随膜厚d的变化关系。得出束缚磁极化子的自陷能由两部分组成：第一部分是由于电子—体LO声子相互作用所引起的（ ）极化子效应;第二部分则是电子－SO声子相互作用引起的。后者又包含两部分,分别是电子与极性膜中两支表面声子相互作用的贡献（ ）。通过对KCl半导体膜的数值计算表明, 和磁极化子的振动频率 随膜厚d的增加而减少;当膜厚大于5nm时,总自陷能 趋于一稳定值。另外,由于稳恒磁场的存在,使磁极化子的自陷能增大,这主要是由于稳恒磁场的存在,使电子—声子间的相互作用增强,极化子效应增大而引起的。     

精确确定半导体材料临界点的能量值

分析表明波长调制反射谱的实质,是介电函数对能量的一级微商。导出了弱电场调制反射谱与介电函数对能量的三级微商成正比,将ＭＯＣＶＤ方法生长的ＧａＩｎＰ以及掺Ｓｉ和掺Ｚｎ三个样品,用椭偏光谱法测量得到可见光区的介电函数谱,并求其一级和三级微商谱。将用于分析电反射谱的三点法推广用于分析介电函数的一级和三级微商谱,得到波长调制和弱电场调制反射谱的实验结果,并与介电函数谱的结果加以比较,使灵敏度和分辨率有很大提高     

Hot-electron trapping activation energy in PMOSFET's undermechanical stress

Mechanical stress-induced change in hot-electron trapping activation energy (E_a) was observed in PMOSFET's for the first time. E_a was found to continuously decrease from 80 meV to 44 meV under compressive mechanical stress (|σ|<100 MPa). From the detrapping behavior after hot-electron injection, E_a is determined by an Arrhenius plot. The new finding thus indicates that the Si-H or Si-SiO₂ interface dangling bonds are distorted by mechanical stress, resulting in E_a lowering     

Influence of electron energy on the characteristics of electron-beam-pumped semiconductor lasers

The influence of electron energy on the characteristics of electron-beam-pumped GaAs lasers is studied experimentally. Increases in the electron energy lead to increases in output power and decreases in beam divergence. Above radiation-damage threshold, a degradation of the laser output with time is observed due to bulk defects created by the beam. These defects are partially self-annealing if radiation is stopped.     

Activation energy determination from low-temperature CV dispersion[semiconductor devices]

The response of semiconductor devices at low temperatures to changes in the voltage across the depletion region is limited by the dielectric relaxation time of the majority carriers in the bulk region. This results in a dispersion of the C-V curves at low temperatures. In this paper, we report a study of the dispersion seen in the accumulation and depletion regions of the C-V curve in n- and p-channel MOS transistors as well as in reverse biased one-sided abrupt junctions. From the admittance measured as a function of temperature and frequency, the dopant energy level is determined. The values of the activation energy measured using the diodes agree well with the corresponding values obtained using MOS devices     

Electric field dependence of TDDB activation energy in ultrathin oxides

A study of the electric field dependence of the TDDB activation energy is presented for 12 nm down to 4.7 nm thin oxides. It is shown that the TDDB activation energy depends linearly on the stress electric field and that this behavior depends strongly on the oxide thickness. Moreover, a relationship between the TDDB activation energy attenuation per MV/cm and the oxide thickness has been found. As will be demonstrated, these results are of great importance for the rigorous estimation of the oxide lifetime of both present and future technologies.     

Finite time of carrier energy relaxation as a cause of optical-power limitation in semiconductor lasers

It is shown that the reason why the maximum attainable optical power in semiconductor lasers is limited is the finite time of carrier energy relaxation via scattering by nonequilibrium optical phonons in the quantum-well active region. The power and spectral characteristics of semiconductor lasers are studied experimentally at high excitation levels (up to 100 kA/cm²) in pulsed lasing mode (100 ns, 10 kHz). As the drive current increases, the maximum intensity of stimulated emission tends to a constant value (“saturates”), and the emitted power increases owing to extension of the spectrum to shorter wavelengths. The intensity saturation is due to limitation of the rate of stimulated recombination, caused by a finite time of the electron energy relaxation via scattering by polar optical phonons. It is found that the broadening of the stimulated emission spectrum is related to an increase in carrier concentration in the active region, which enhances the escape of electrons into the waveguide layers. As the drive current increases, the carrier concentration in the waveguide reaches its threshold value and there appears an effective channel of current leakage from the active region. The experiment shows that the appearance of a band of waveguide lasing correlates with a sharp drop in the differential quantum efficiency of a semiconductor laser.     

Pulse energy gain saturation in subpico- and picosecond pulseamplification by a traveling-wave semiconductor laser amplifier

Optical pulses with durations ranging from 0.49 to 21 ps are amplified by a traveling-wave semiconductor laser amplifier. The pulse energy gain is determined by pulse energy only. The dependence of pulse energy gain on output pulse energy does not change in the pulse duration range. The saturation characteristics are successfully explained by a four-level system model     

太阳能供电半导体制冷技术在低温储粮中的实验研究

粮食储藏问题历来至关重要。近几年来,研究表明,低温储藏能够很好地解决传统储粮方法中的虫害、霉变等带来的损失。本文设计一个基于太阳能供电驱动半导体制冷的系统,通过ATMEGA16单片机来控制半导体制冷,实现制冷的目的,采用小型密闭空间来模拟武汉某粮仓的实验,通过对实验数据定性和定量分析的方法,得出当目标温度在22℃和18℃制冷效果较好,当目标温度在14℃时制冷效率降低,误差变大。     

A novel energy filter using semiconductor superlattices and itsapplication to tunneling time calculations

An artificial quantum-mechanical filter using superlattice structures is proposed in this paper. By gradually changing the barrier widths of a superlattice according to a Gaussian function, a broad-band and almost zero sidelobe transmission profile can be obtained. The WKB approximation is applied to demonstrate the phenomena of abrupt change of transmission profile. The proposed structure allows the incident electrons to be nearly totally transmitted when the impinging electron energy is in the passband. On the other hand, a complete reflection occurs when the impinging energy is in the stopband. By adjusting the structure parameters, the desired passband and stopband of such a filter can be obtained. Time evolution of an electron wavepacket moving through the structure is calculated by numerically solving the time-dependent Schrodinger equation. Numerical results clearly demonstrate the characteristics of total transmission and reflection. By simulating the movement of a totally transmitted wavepacket, ambiguity results from the nature of the wavepacket in the determination of electron tunneling time can be avoided. The generalized concept of matched quantum-mechanical wave impedance (QMWI) analogous to transmission line theory is presented to explain the occurrence of total transmission of the proposed structure. The tunneling time (τ_QMWI) calculated based on the concept of QMWI is compared with the accurate tunneling time obtained by our simulation     

Adaptive algorithms for sensor activation in renewable energy based sensor systems

Upcoming sensor networks would be deployed with sensing devices with energy harvesting capabilities from renewable energy sources such as solar power. A key research question in such sensor systems is to maximize the asymptotic event detection probability achieved in the system, in the presence of energy constraints and uncertainties. This paper focuses on the design of adaptive algorithms for sensor activation in the presence of uncertainty in the event phenomena. Based upon the ideas from increase/decrease algorithms used in TCP congestion avoidance, we design an online and adaptive activation algorithm that varies the subsequent sleep interval according to additive increase and multiplicative decrease depending upon the sensor’s current energy level. In addition, the proposed algorithm does not depend on global system parameters, or on the degree of event correlations, and hence can easily be deployed in practical scenarios. We analyze the performance of proposed algorithm for a single sensor scenario using Markov chains, and show that the proposed algorithm achieves near-optimal performance. Through extensive simulations, we demonstrate that the proposed algorithm not only achieves near-optimal performance, but also exhibits more stability with respect to sensor’s energy level and sleep interval variations. We validate the applicability of our proposed algorithm in the presence of multiple sensors and multiple event processes through simulations.