Avalanche breakdown and surface deep-level trap effects in GaAsMESFET's

Time-dependent numerical simulations have been performed to investigate avalanche breakdown and surface deep-level trapping effects in GaAs MESFETs. The model is based on a combination of bipolar drift-diffusion transport, impact ionization, and a dynamic surface charging mechanism. A realistic trapping process is introduced into the surface trap model from which the spatial distribution of surface charge density is determined. The basic breakdown mechanisms, gate-bias-dependent breakdown voltages, and effects of surface charges are demonstrated. It is shown that the surface deep-level traps have a pronounced effect on the breakdown phenomenon     

碲镉汞表面处理中异常现象的分析及控制（英文）

表面处理是碲镉汞（HgCdTe）红外探测器芯片制作流程的开始,其效果会直接影响芯片的良品率。采用金相显微镜、扫描电子显微镜（SEM）和X射线光电子能谱（XPS）分析手段,探究了碲镉汞表面处理工艺中四种典型的表面异常现象的成因,并提出了相应的控制措施。水痕缺陷的形成机理为吸氧腐蚀,通过稳定氮气气流快速将晶片表面吹干可以控制该缺陷的形成;染色现象的成因为腐蚀液被不均匀稀释或腐蚀液被水等杂质污染,工艺中应严格避免杂质的污染,腐蚀结束后快速冲洗表面;圆斑现象是由于缺陷处吸附清洗液引起,采用异丙醇浸泡后再干燥可以降低该缺陷出现的概率;甲苯与HgCdTe表面直接接触时会导致碲镉汞表面粗糙度增大,工艺中需要避免甲苯和HgCdTe表面的直接接触。     

Analysis of the narrow gate effect in submicrometer MOSFET's

The narrow gate effect produces an increasing threshold voltage with decreasing gate width. Our previous approximate formulae, based on shifting the gate-edge position, predicts the variation of the threshold voltage with gate width accurately in the super-micrometer width range, but error begins to increase when the gate width is less than a critical valueW_{min}which is about 1 µm for 200-A gate oxide 7000-A field oxide and2 times 10^{16}cm^-3substrate doping. The physical reason of this error is delineated and combined with two-dimensional numerical analyses to give a new formulae based on shifting the gate-center position as the gate width narrows. The parameters of this new formula may be obtained either from two-dimensional computation or experimental measurements. The error is less than 2 percent at a dc gate bias of 5 V.     

Analysis of surface-state and impact-ionization effects on breakdown characteristics and gate-lag phenomena in narrowly recessed gate GaAs FETs

Effects of surface states and recess structures on breakdown characteristics of GaAs MESFETs are studied by two-dimensional (2-D) analysis. It is shown that the breakdown voltage could be raised when moderate densities of surface states are included. However, in a case with relatively high densities of surface states, the breakdown voltage could be drastically lowered when introducing a narrowly recessed gate structure. Effects of impact ionization on gate-lag phenomena in GaAs MESFETs are also studied. It is shown that the gate-lag becomes weaker when including the impact ionization. This is attributed to the fact that the potential profiles along the surface are drastically changed when the surface states capture generated carriers. It is suggested that there is a tradeoff relationship between raising the breakdown voltage and reducing the gate-lag.     

Temperature effect on gate leakage currents in gate dielectric films of GaAs MOSFET

The gate dielectrics of Ga₂O₃(As₂O₃) of the GaAs MOSFET were prepared by a low-cost and low-temperature liquid-phase chemically enhanced oxidation method. The temperature and oxide thickness dependence of gate dielectric films on GaAs MOSFET have been investigated. The leakage current and dielectric breakdown field were both studied. Both gate leakage current density and breakdown electrical field were found to depend on the oxide thickness and operating temperature. The increasing trend in gate leakage current and the decreasing trend in breakdown electrical field were observed upon reducing oxide thickness from 30 to 12 nm and increasing operating temperature from −50°C to 200°C.     

Charging effect of Si nanocrystals in gate oxide near gate on MOS capacitance

MOS structure with Si nanocrystals embedded in the gate oxide close to the gate has a much larger capacitance compared to a similar MOS structure without the nanocrystals. However, charge trapping in the nanocrystals reduces the capacitance dramatically, and after most of the nanocrystals are charged up the capacitance is much smaller than that of the MOS structure without nanocrystals. An equivalent-capacitance model is proposed to explain the phenomena observed.     

One-dimensional analysis of turnoff phenomena for a gate turnoff thyristor

Turnoff phenomena for a one-dimensional gate turnoff thyristor (GTO) are investigated using exact numerical solutions of a full set of semiconductor device equations. It is shown that the time responses of the hole and the electron densities around the center junction J2 are responsible for the dynamic behavior of the GTO. The storage time almost corresponds to the time period required for J2 to come out of saturation. The fall time is the period from the coming out of saturation of J2 to the point when the cathode emitter junction recovers. Time variations in the rates of replenishment and removal of holes in the p-base during the dynamic turnoff process are discussed, and an understanding of the switching mechanism, which is not obtainable in the generally used static transistor analogy, is obtained. Though a one-dimensional model is employed in this paper, it still provides a great deal of insight into the device's operation.     

Physics of ultrafast phenomena in solid state plasmas

Over the past half-decade measurements of the nonlinear, nonequilibrium optical properties of the germanium solid-state plasma have been carried out in several laboratories. These measurements involve, for example, the ultrafast relaxation of optically-excited electron-hole distributions in semiconductors and the photoluminescence spectrum of Ge at high excitation intensities. Here, we review our present theoretical understanding of these experiments, and we discuss the theoretical limitations. We also extend our previous model, through a simple calculation, to include carrier diffusion.     

Resonant phenomena in laser excitation of surface waves on solids

Excitation of surface waves by a moving laser beam has been studied both theoretically and experimentally. Using periodic surface structures as an example, it is demonstrated that the type of excited wave and the rate of its growth depend resonantly on the beam velocity. Experimental data show that resonant excitation of different periodic surface structures can change the spatial distribution of the absorbed laser energy     

Effects of surface states on relaxation phenomena in MOS capacitors

A numerical simulation of a silicon MOS capacitor pulsed from equilibrium into deep inversion has been performed with a view to accurately investigating the effects associated with surface states. A continuum of acceptor surface states has been assumed across the energy gap but, of course, the conclusions may be extended to the case of donor-like states. The results of the calculations show that soon after application of the voltage step a considerable portion of the trapped electrons is released from the upper half energy gap into the conduction band giving rise to a spike in the external current. The emission of these electrons is so rapid that it cannot be detected by the usual slow response current meter, nor is it able to induce any relevant variation into the depletion layer width and, consequently, into the high-frequency capacitance. At the same time, electrons trapped in the surface states disappear also through recombinations with holes generated in the bulk. During a time interval, which turns out to be small in comparison to the duration of the whole transient, every hole generated recombines at the surface giving rise to a small delay in the formation of the inversion layer. After that this latter begins to build up and surface states behave as if they were in a quasi-equilibrium condition with the valence band.     

Origins and characterization of low-frequency noise in GaAsMESFET's grown on InP substrates

An experimental study of the low-frequency noise in GaAs MESFET's grown on InP substrates is reported. The influence of the biases applied to the gate, backgate, and drain in the ohmic region is investigated in order to identify and characterize the 1/f noise origin. We find that this noise can be explained by carrier number fluctuations in the channel and related to trapping phenomena. The traps responsible for this noise are located near the channel-buffer interface. Moreover, the noise behavior exhibits for a well-defined gate voltage, corresponding to the case where the drain current flows near the channel-buffer interface, a GR-type (Lorentzian) noise spectrum emerging from a quite general 1/f noise. This last spectrum corresponds to a single trap level with a density of N_T=10¹⁶ cm^-3 and a time constant τ=1.8 ms which may be attributed to crystal defects present in the GaAs layers     

Light-triggering phenomena on thyristors with an n-emitter layer over the light-sensitive gate area

Turn-on phenomena of a light-activated thyristor are analyzed using a one-dimensional numerical model that consists of the full set of semiconductor device equations, including the optically generated current and the effect of the shorted emitter. Results indicate that the photocurrent Ipis induced by photovoltaic effects of then_{E}-p_{B}junction and that its flow is in the reverse direction of the anode current IA. Consequently, Ipcirculates through the p-base, the short path placed across then_{E}-p_{B}junction and the n-emitter resulting in a contribution to the light triggering, in addition to that of IAcaused by the conventionalP_{B}-n_{E}-p_{E}transistor action. In order to confirm the predicted behavior of the photocurrents, light-triggered 4-kV devices were fabricated. The experimental results thus obtained confirm the conclusions drawn from the model analysis.     

The relaxation phenomena of positive charges in thin gate oxideduring Fowler-Nordheim tunneling stress

In this study, new relaxation phenomena of positive charges in gate oxide with Fowler-Nordheim (FN) constant current injections have been investigated and characterized. It was found that the magnitudes of applied gate voltage shifts (ΔV_FN) during FN injections, after positive charges relaxed or discharged, have a logarithmic dependence with the relaxation time for both injection polarities. The results can derive the relationship of transient discharging currents, that flow through the oxides after removal of the stress voltage, with the relaxation time. We have shown that the current has a 1/f dependence for both injection polarities which can be also derived from the tunneling front model. The effects of oxide fields (lower than the necessary voltage for FN tunneling) and wafer temperatures (373 and 423 K) for the relaxation of positive charges are also studied     

Hot hole gate current in surface channel PMOSFETs

This paper reports the observation of a new hot hole component of the gate current of p⁺-poly gate pMOS transistors. The phenomenon is characterized as a function of drain, gate, and substrate bias on devices featuring different oxide thickness and drain engineering options. The new hole gate current component is ascribed to injection into the oxide of substrate tertiary holes, generated by an impact ionization feedback mechanism similar to that responsible of CHannel Initiated Secondary ELectron injection (CHISEL) in nMOSFETs     

SnAgCuY钎料表面Sn晶须的旋转生长现象

研究了Sn3.8Ag0.7Cu1.0Y钎料表层上YSn3稀土相表面Sn晶须的生长行为。结果表明:室温时效条件下在YSn3的表面会出现Sn晶须的快速生长现象,生长速度最快可达10–10m/s,长度最长可达200μm。YSn3稀土相氧化的不均匀性是导致Sn晶须在生长时产生各种旋转现象的主要原因。     

Analysis of gate shot noise in MOSFETs with ultrathin gate oxides

The impact of gate shot noise associated with gate leakage current in MOSFETs is studied by means of analytical models and numerical device simulation. The effects of shot noise on the main two-port noise parameters (minimum noise figure, equivalent noise resistance, and optimum source admittance) and their dependence on oxide thickness and on the level of tunneling leakage current are analyzed.     

三态门总线传输电路的Multisim仿真方案

基于探索仿真三态门总线传输电路的目的,采用Multisim10仿真软件对总线连接的三态门分时轮流工作时的波形进行了仿真实验测试,给出了仿真实验方案,即用Multisim仿真软件构成环形计数器产生各个三态门的控制信号、用脉冲信号源产生各个三态门不同输入数据信号,用Multisim仿真软件中的逻辑分析仪多踪同步显示各个三态门的控制信号、数据输入信号及总线输出信号波形,结论是仿真实验可直观形象地描述三态门总线传输电路的工作特性,所述方法的创新点是解决了三态门的工作波形无法用电子实验仪器进行分析验证的问题。