碳纳米管场致发射结构的研究

碳纳米管以其特有的电学性质而成为一种优良的冷阴极材料。在场致发射器件中，真空度是决定发射稳定性的一个重要因素。如果碳纳米管阴极附近的真空度太低，将产生打火、气体电离、离子回轰阴极等问题，将导致阴极发射电流的迅速衰减。本文通过对基于碳纳米管冷阴极的二极管和三极管的场发射特性的实验，分挤了残余气体压强与外加电压、发射体工作时间的关系以及碳纳米管阵列的I-E曲线，利用这些结果可以优化碳纳米管场致发射结构的设计。     

Kilovolt extraction of dense electron beams from synthesized-plasma cathodes

Electron beams with a continuous current density of 800 A/cm²were extracted from a synthesized-plasma hollow cathode. The beams were accelerated up to potentials of 1.2 kV, through the potential of maximum ionization probability at about 16 volts. There was no accompanying oscillation or gas breakdown. This high voltage operation was made possible by collimating the cesium vapor entering the hollow cathode. The collimation, which was accomplished by use of a narrow slit at the "top" of the cathode, caused the vapor to flow along the cathode wall surface and away from the exit aperture. This minimized escape of neutrals into the high voltage region. The cathode was tested for 200 hours without any signs of degradation. The cathode lifetime is predicted to be several thousand hours at the highest cathode temperature (2425°K) employed in these studies. The extracted 0.030-in diameter beam of 0.250-in length had an electron temperature of less than twice cathode temperature. Longer beams, such as would be used in actual microwave tubes, would require magnetic confinement.     

Mechanism of negative transconductance in heterostructurefield-effect transistors

In most heterostructure field-effect transistors the drain current at very large gate voltages drops with an increase of the gate voltage leading to a negative device transconductance. Based on the analysis of the gate and channel current distributions in such devices, it is shown that the negative transconductance at large gate currents is related to the dramatic change in the electric field distribution in the channel and to the saturation of the density of the two-dimensional electron gas in the channel. Under such conditions the electric field increases at the source side of the channel where the gate current primarily flows. When the electric field at the source side exceeds the electric field at the drain side of the channel, the device transconductance becomes negative. This is related to a higher voltage drop near the source side of the channel causing a partial depletion in the channel     

Surface area measurement by diffusion-limited current

The method and equipment discussed here for measuring the surface area of conductors in the electroplating process is based on the diffusion-limited current method (DIM). "Diffusion limited current" means a current limited by the diffusion rate of cations towards the cathode. In electrodeposition, at a certain level of potential, the overall rate-limiting step is the diffusion of cations towards the cathode. The application of the voltage determines the concentration of electroactive ions at the cathode-electrolyte interface. If this voltage is negative enough, the concentration of ions at the interface is zero. At this moment, the current is limited by the diffusion rate of cations towards the cathode. It has an excellent ability to measure rapidly and precisely the surface area of conductors with very complex shapes, especially for bodies with sharp edges.     

Studies on non-thermal atmospheric pressure plasma process conditions for groove formation on silicon nitride for silicon solar cells

Fabrications of narrow electrode grooves for front electrodes on single crystalline silicon solar cells were examined using surface discharges, in which the electrode grooves were formed by etching a silicon nitride (SiN) film on substrates. The surface discharge could effectively etch the SiN film within 10 s and that a high etching rate more than 1800 nm/min was obtained. An optimum ratio of Ar gas, which was enough to maintain the formation of innumerable surface streamers, was 2.3 times larger than that of etching gas, and a short-term etching with the high discharge voltage was effective to narrow groove width.     

铝阴极氧化对同位素氦氖气体放电参数的影响

铝通常用作气体放电装置的阴极,经过表面氧化达到提高电子发射和耐正离子轰击的效果。本文采用自制的理想平行电极放电管对铝阴极做不同时间的放电氧化,模拟环形氦氖激光器的放电过程,研究了铝阴极氧化对气体放电参数(着火电压、灭火电压和正常辉光放电最大电流密度)的影响。根据实验测得的各个参数值,结合辉光放电的公式,计算了每个放电参数相应的阴极次级电子发射系数γ随氧化时间变化的值,结合电镜对氧化表面含氧量的测试分析了实验发现的现象。     

Low-voltage mercury-alkali metal arc

Measurements of the arc voltage and electron temperature were made on low-pressure arcs utilizing a mercury-pool cathode containing various concentrations of alkali metals. The arc-burning voltage was substantially lower than the pure mercury arc and the minimum arc voltage depended on the concentration of the alkali metal and ambient tube temperature. The measurements suggest that there are three processes which collectively are responsible for the arc behavior. These are a lower anode work function, a Penning two-stage ionization process of alkali metal atoms by mercury metastables and an improved electron emission by reliable anchoring of the cathode spot. With the addition of small amounts of alkali metal the cathode spot emission zone was stable on a molybdenum anchor at currents as high as 200 a. The cathode fall potential was the order of 4 v. It is shown that the voltage reduction is mainly in the cathode fall region and that it is lower for rubidium than cesium, potassium or sodium in the preceding order.     

Generation mechanism of gate leakage current due to reverse-voltagestress in i-AlGaAs/n-GaAs HIGFETs

Device degradation characterized as an increase in the gate leakage current due to continuous reverse-voltage stress was investigated for a 0.35-μm WSi gate i-AlGaAs/n-GaAs doped channel HIGFET (heterostructure insulated-gate field-effect transistor). The gate leakage current, which was dominated by a hole current generated by impact ionization, was found to increase after the application of a gate-to-drain voltage of -6 V for a certain period. The occurrence of the impart ionization was evidenced by the generation of a substrate current and by the negative temperature coefficient of the gate current. The degradation was retarded at an elevated temperature, indicative of hot-carrier-related degradation. The degraded device also showed an ohmic-like gate leakage current. Subsequent annealing at temperatures above 300°C significantly restored the current-voltage (I-V) characteristics. From these observations, a degradation model was developed in which hot holes generated by impact ionization are trapped in the insulator/semiconductor interface, contracting the surface depletion region and thereby increasing the electric field near the gate-edge. A surface treatment using CF₄ plasma was used to suppress the degradation. An FET fabricated using this treatment showed a remarkable decrease in degradation     

Semiconductor streamer lasers

A new method of electrically exciting generation of light behind the ionization front in streamers is theoretically and experimentally considered. Light intensity ofsim 10^{9}W/cm²was generated in CdxSe1-xand ZnSe crystals from radiation regions having characteristic dimensions ofsim5 mum, and moving with velocitiessim3.10^{8}cm/s.     

Investigation of the threshold voltage turn-around effect in long-channel n-MOSFETs due to hot-carrier stress

In this paper, we have investigated the turn-around effect of the threshold voltage (V_th) shift in the case of an n-type long channel MOSFET during hot-carrier stress. This effect is explained by the interplay between interface states and oxide traps, i.e. by the partial compensation of the rapidly created oxide charges by the more slowly created interface states. Significant hole trapping is observed from the negative shift of the threshold voltage during the first seconds of stress. Afterwards, V_th has switched to the positive voltage direction due to the negative charging of interface traps after relatively long stress time. To analyze this phenomenon in detail, a refined extraction technique for the defect distribution from charge-pumping measurements has been employed. Additionally, the obtained results have been explained by our physics-based model of hot-carrier degradation which considers not only channel electrons but also secondary holes generated by impact ionization. In spite of the small hole contribution (compared to that of electrons) to the total defect creation, its impact on the threshold voltage shift is comparable with the electronic one. The reason behind this trend is that hole-induced traps are shifted towards the source, thereby more severely affecting the device behavior.     

Vacuum arc ion currents and electrode phenomena

Properties of dc vacuum arcs between copper electrodes are studied in both a vacuum interrupter and a metal walled arc chamber. Maximum ion currents of ∼8 to 20 percent of the arc current (100 to 3000 A) are drawn from the diffuse arc plasma when the bounding metal wall or shield is biased negative. This maximum ion current is a fundamental arc property independent of wall diameter, anode diameter, and electrode spacing. The geometric dependence of the wall ion current, together with observations of isotropic vapor and ion emission from the cathode, indicates that the cathode regions adjacent to the cathode spots are the predominant sources of ionization for the plasma. Assuming single ionization, 55 percent of the vapor leaving these regions is ionized. Starvation phenomena in the anode region remote from the cathode spots lead to anode voltage drop and anode spot formation. Post arc currents reveal a mean ion speed during arcing of ≈8×10⁵cm/s. This mean speed may be acquired in the cathode region by acceleration from a potential maximum.     

Arc structure, arc motion, and gas pressure between laterallyenclosed arc runners

Arc motion along parallel arc runners tightly enclosed by lateral walls was investigated experimentally, both with and without an exhaust barrier at the outlet. High speed movies (33 000 frames/s) were taken and the gas pressure was measured at several locations along the path of arc motion. The measurements show how both arc shape and motion depend on the parameters arc length (5-15 mm) and exhaust constriction. In many cases both arc shape and arc motion were influenced by a plasma volume forming a “nose” in front of the arc next to one of the electrodes. Spontaneous formation of an anode spot and/or a cathode spot in front of the arc may ignite a parallel current path and initiate a commutation process. The plasma volume in front of the arc is less significant at low electrode distance, high arc current, high blast field, and in more realistic chamber geometries with an exhaust barrier. Cold gas shock waves hitting the arc strongly influence both arc motion and shape. Simulation of arc motion may be a helpful tool in order to save expensive experiments when designing low voltage miniature circuit breakers. The high speed movies showed that the arc motion is sometimes strongly influenced by commutation processes requiring a very complex arc model     

Stress voltage polarity dependence of thermally grown thin gateoxide wearout

Gate oxide wearout for thermally grown 57-190-A SiO₂ films in a polycrystalline silicon-SiO₂-Si structure prepared on n-type and p-type wafers was studied by examining time-dependent dielectric breakdown (TDDB) under 1-mA/cm² constant current with positive and negative voltages at 250°C. TDDB lifetimes for positive voltage stress are more than one order longer than those for negative voltage stress. TDDB lifetimes depend on oxide thickness, that is, they increase for positive voltage stress and decreases for negative voltage stress with decreasing oxide thickness. They also depend on whether the oxide films are prepared on n-type or p-type wafers. After the positive voltage TDDB stress, negative charges are predominantly produced in the oxide layer, and the electric field at the cathode in the oxide film slightly decreases. On the contrary, after the negative voltage TDDB stress, positive charges are predominantly produced at the cathode in the oxide layer and the electric field at the cathode is built up, resulting in an increase in Fowler-Nordheim tunnel current flowing though the oxide film     

Plasma addressing for flat-panel displays

An active-matrix technique that is functionally identical to an array of thin-film transistors (TFTs) but does not rely on semiconducting materials or the manufacturing processes normally associated with integrated circuits is described. The approach avoids the manufacturability problems that have hampered the development of large TFT displays. The new addressing technology relies on the properties of a confined, ionized gas, and is called plasma addressing (PA). It uses the gas to perform electrical switching. When the gas is in an ionized state, it is conducting; when in a deionized state, it is nonconducting. The difference between the conductivity of the gas in its conducting and nonconducting states is easily 10 orders of magnitude. When the cathode voltage is switched on and the gas is ionized, a properly located probe electrode appears electrically connected to the anode, which can be at ground potential. When the cathode voltage is reduced below the plasma sustaining voltage, the plasma is extinguished and the probe electrode is no longer connected to the anode. Thus, the cathode connection can be thought of as a control or `gate' electrode. PA has been used to address twisted nematic and polymer-dispersed liquid crystals. The technology's inherently wide voltage range also allows it to be used for addressing thin-film electroluminescent films     

A self-consistent model for negative glow discharge lasers: thehollow cathode helium mercury laser

A model for negative glow metal-vapor ion lasers that self-consistently describes the dynamics of the negative glow and the cathode sheath regions of the discharge has been developed. The model computes the electron energy distribution and the population of relevant excited states in the negative glow self-consistently with the charged particles fluxes and electric field distribution in the cathode sheath. Its application to the study of the helium-mercury charge transfer ion laser is reported. The model accurately depicts the operation of a hollow cathode in the laboratory, where for a defined cathode geometry and material, the discharge characteristics are determined by the selected discharge voltage and the gas pressure. The laser output power calculated as a function of the discharge parameters is in good agreement with experimental measurements reported in the literature. The model can be modified to simulate other negative glow discharge lasers, such as electron-beam pumped CW ion lasers     

Hot electron degradation effects in 0.14 μm AlInAs/GaInAs/InP HEMTs

We report on hot electron stress measurements on 0.14 μm MOCVD grown AlInAs/GaInAs/InP HEMTs. The stress measurements increase the drain-source current and hence induce a temporary negative shift in the threshold voltage in unpassivated HEMTs. A permanent negative shift in the threshold voltage has been obtained in passivated HEMTs. The observed degradation (temporary/permanent) is due to the storage of positive charges (created by the impact ionization in the channel) in the Schottky AlInAs layer (temporary) or at the interface of semiconductor-passivation layer (permanent). For a given drain-source bias, a shift in the threshold voltage is larger in the gate-source bias region where the device has a maximum transconductance value.     

准二维电子系统的远红外栅压比谱

讨论应用快扫描傅里叶变换光谱仪研究异质结表面及量子阱中二维电子气的高频动力学性质，利用制备有金属栅极的异质结样品的肖特基场效应特性，通过光谱仪控制栅压门电源交替选择栅压扫描，获得了二维电子气的吸收栅压比谱，由此观察到该低维系统的几类基本红外激发，包括回旋共振、二维等离子激元及电子子能带间的共振跃迁     

Space-charge striations

The non-local nature of impact ionization is modelled using lucky-drift theory with the assumption that the relevant electric field is the average field, but that the relevant drift velocity is that associated with the local field. The carrier density relevant for impact ionization is also taken to be non-local. The model is applied to the case of a thin film insulator with Fowler-Nordheim injections of electrons at the cathode. For clarity's sake we avoid considering the excitation of holes and limit attention to the ionization of a set of occupied deep-level states present in high concentration. We show that the non-local nature of the ionization process reduces the local field markedly, resulting in a pile-up of free electrons to maintain current continuity in the rest of the film. This is contrasted to the prediction of local-impact-ionization theory, in which the field is reduced merely to that necessary to sustain a small level of ionization. Under certain circumstances space-charge striations are produced analogous to the situation in gas discharge, and for some film thicknesses a NDR occurs.     

相对论电离波前导致的频率上移

介绍了电磁波与相对论电离波前相互作用的理论和实验进展情况。超短脉冲强激光可以使气体在极短时间内完全电离而形成相对论运动的电离波前,电磁波探针与该波前相互作用会导致频率上移,利用这种特性可能实现一种新的大范围激光调谐机制。     

电子枪发射电流的数值计算

本文根据热电子发射的统计理论,运用无穷大平板二极管中考虑电子纵向热速度效应的电位状态与普通电子枪中阴极前面的电位状态相等效的处理方法,编写了电子枪的计算机程序,得到了计算的电子枪发射电流值与实测的电流值相一致的结果,文中还通过计算分析指出,在计算电子束管电子枪的发射电流时,必须考虑电子的纵向热速度效应,其计算的电流值比3/2次方定律的电流值大,且更接近实测结果;微波管强流电子枪中,电子纵向热速度效应在低工作电压下比在高工作电压下影响大些,但总的来说,比在电子束管中的影响小得多;电子纵向热速度效应对发射电流的影响随阴极的发射电流密度与阴极发射本领差别的增大而增加,但当这一差别大于一定值后,这种影响的大小趋于恒值。