Growth conditions to achieve mobility enhancement in AlxGa1?xAs-GaAs heterojunctions by m.b.e.

Modulation doped Al0.25Ga0.75As-GaAs heterojunctions have been prepared by molecular beam epitaxy (m.b.e.). Al0.25Ga0.75As layers were doped with Si to a level of ~ 3 × 1017 cm?3, whereas the GaAs layers were either unintentionally doped, doped lightly n-type with Sn, or doped lightly p-type with Be. Heterojunction structures having single and multiple periods have shown enhanced mobility only with the AlxGa1?xAs layer at the surface and the GaAs layer underlying. These results represent the first report that electrons spill over only into the underlying GaAs layer from the top AlxGa1?xAs layer.     

V.P.E. GaAs m.e.s.f.e.t. structure using oxygen injection during buffer layer growth

GaAs m.e.s.f.e.t. structures with high-resistivity buffer layers were prepared by introducing oxygen into the deposition system during growth. The electrical properties of the buffer layers are independent of the oxygen content of the gas phase over a large range of partial pressures. The characteristics of devices prepared with such layers are excellent.     

Relaxation l.s.a. mode in InP

What are believed to be the first convincing observations of relaxation l.s.a.-mode operation in InP are reported. Devices fabricated from vapour-phase epitaxial material have shown the characteristic `signatures? of the mode in oscillators operated in S- and X-bands. So far, conversion efficiencies have not exceeded those for comparable samples in GaAs, almost certainly owing to remaining material limitations in the relatively thick active layers. The significance of the results lies, in practical terms, in the promise of high-peak-power sources with acceptable efficiencies, and, in diagnostic terms, in the derived information on the magnitude of the fundamental transferred-electron characteristic peak/valley ratio in InP and in achievable material quality factors for thick epitaxial layers.     

Research progress in electrophotography in the U.S.S.R. and Eastern Europe

A review of the latest investigations carried out in Bulgaria, East Germany, Poland, and the U.S.S.R. is presented. The discharge mechanisms both in dark and under illumination are being analyzed for two types of electrophotographic layers--with a binder and without it. In both cases, the discharge mechanism does not only depend on the layer type, its structure and technology, but also on the conditions of charging and discharging. It is shown that the photo-discharge mechanisms of selenium electrophotographic layers and of zinc oxide layers with binder differ in principle. The characteristics of As-Se electrophotographic layers and electrophotographic process with an effective quantum yield exceeding unity have been considered. Some works investigating the prospects of application of organic photoconductors in electrophotography have been reviewed. Information on the electrophotographic copiers and electrophotography for medical purposes is also provided.     

Preparation and properties of GaAs layers for novel f.e.t. structures

N-type GaAs/Ga0.4Al0.6As heterostructures have been grown on semi-insulating GaAs substrates using metal-organic chemical vapour deposition. The GaAs layers were mounted on insulator supports and the substrates and Ga0.4Al0.6As removed using a preferential etching procedure. The preparation and electrical properties of submicrometre thick insulator-supported n-type GaAs layers are described.     

Lossless compression of color map images by context tree modeling.

Significant lossless compression results of color map images have been obtained by dividing the color maps into layers and by compressing the binary layers separately using an optimized context tree model that exploits interlayer dependencies. Even though the use of a binary alphabet simplifies the context tree construction and exploits spatial dependencies efficiently, it is expected that an equivalent or better result would be obtained by operating directly on the color image without layer separation. In this paper, we extend the previous context-tree-based method to operate on color values instead of binary layers. We first generate an n-ary context tree by constructing a complete tree up to a predefined depth, and then prune out nodes that do not provide compression improvements. Experiments show that the proposed method outperforms existing methods for a large set of different color map images.     

在20~#钢表面激光C·N和C·B合金化的研究

一、引言非金属元素合金化就是将含有碳、氮、硼元素的化合物,按一定的比例制备成添加物,涂敷在金属材料的表面上,在激光束的辐照下,使涂层和基体薄层同时达到熔化程度。在熔池中,添加元素和基体元素同处于液体状态下,由于液体表面张力效应和重力的作用,熔池中各种元素之间相互扩散,混合,移去加热的激光束,熔池吸收大量的热量由基体迅速地传走,而表面急剧冷却,凝固后,基体表面便形成含有添加元素的合金层。采用激光C·N和C·B合金化与常规化学共渗处理相比其优点是:激光合金化     

Si间隔层对Al(1wt.%Si)/Zr极紫外多层膜热稳定的作用研究

为了提升Al/Zr多层膜的热稳定性,采用直流磁控溅射方法制备了18个带有不同厚度Si间隔层的Al(1 wt.%Si)/Zr多层膜,并将这些样品分别进行了不同温度(100~500 ℃)的真空退火,退火时间为1 h.利用X射线掠入射反射(GIXR)和X射线衍射(XRD)的方法来研究Si间隔层对Al/Zr多层膜热稳定性的作用.GIXR测量结果表明:随着Si间隔层厚度的增大,Al膜层的粗糙度减小,而Zr膜层的粗糙度增大;XRD测量结果表明:Al和Zr膜层粗糙度的变化是由于退火后膜层中晶粒尺寸不同造成的.相比于没有Si间隔层的Al/Zr多层膜,引入厚度为0.6 nm的Si间隔层可以有效提升Al/Zr多层膜的热稳定性.     

White-emitting a.c. electroluminescent powder layers for flat-panel television

For application in future flat-panel television, where a thin-film transistor matrix on glass addresses a superimposed e.l. powder layer, we have developed e.l. layers which emit white light by using part of the blue e.l. emission to excite the fluorescence of organic dyes which are dissolved in the resinous embedding medium. Using a monograin particle layer and a black back electrode, we have achieved high visual contrast in a bright ambient, and operation at less than 50 V. Fabrication is described. The design can be extended to colour-t.v. panels.     

GaAs m.e.s.f.e.t. prepared by organometallic chemical vapour deposition

GaAs m.e.s.f.e.t.s with gate dimensions of 1.5 ?m × 300 ?m were fabricated in the epitaxial layers grown by organometallic chemical vapour deposition (o.m.c.v.d.) technique. The average saturation velocity in the channel was deduced to be 1.3 × 107 cm/s and is equal to that of epitaxial layers grown by AsCl3 chemical vapour deposition (c.v.d.). The velocity degraded region was confined to within about 350 ? of the interface. A gain of 10 dB and a noise figure of 3 dB with an associated gain of 5.5 dB at 8 GHz were measured.     

n- and p-channel m.o.s.f.e.t.s as Rayleigh-surface-wave detectors

We have studied the piezoresistance effect in an m.o.s.f.e.t. structure used as a Rayleigh-surface-wave transducer. The investigation was carried out over a large frequency range about a central value of 100 MHz. Results for silicon?m.o.s.f.e.t. n- and p- channel inversion layers are given.     

热释电红外探测器吸收层研究

通过在N2气中蒸发金,成功地制备出金黑吸收层,并测试了金黑层的若干性能,结果表明金黑是一种优良的吸收红外线的材料.改进了原工艺流程,提高了金黑层的附着力,使之实用化.     

Very-high-purity InP l.p.e. layers

Very-high-purity l.p.e. InP layers with a ?77 of 67 000cm2/Vs and an n77 of 1.1 × 1015 cm?3, virtually uncompensated, having a low freeze-out ratio of 1.03, and with continuous surfaces with terraces but no inclusions, have been successfully grown, after the residual silicon donor in the melt has been baked away in H2 with trace amounts of H2O.     

Micrometre-gate m.e.s.f.e.t.s on laser-annealed polysilicon

Schottky-barrier field-effect transistors (m.e.s.f.e.t.s) have been fabricated on uniformly doped laser-annealed polycrystalline silicon deposited on a silicon nitride insulator. The devices, which had aluminium Schottky-barrier gates and diffused n+ sources and drains but nonoptimised channel profiles, had about 65% the gm values of similar but optimised devices made on s.o.s. layers. Performance of these devices is considered adequate for certain innovative integrated-circuit technologies.     

MOS Integrated circuits fabricated on multilayer heteroepitaxial silicon-insulator structures for applications to 3-D integrated circuits

Multiple layers of single-crystal silicon and boron phosphide have been grown on silicon and silicon-on-sapphire substrates. Up to four layers have been grown on silicon and two layers on silicon-on-sapphire. The quality of the silicon layers was confirmed by fabricating PMOS integrated circuits on the top silicon layer in all of these structures. The integrated circuits contained individual transistors, p-n diodes, inverters, flip-flops, and ring oscillators. All circuits successfully operated on all of the layers tested. The transistor mobilities tended to drop as more layers were added to the structure. The delay time of the ring oscillators rose as the number of layers increased reflecting the drop in transistor mobilities. By fabricating circuits on the various layers, the quality of the individual layers has been shown to be sufficiently high to consider this material combination as a possible candidate for 3-D integrated circuits. The boron phosphide was used not only as an insulator but also for the fabrication of vertical resistors and p-n junctions.     

Modification of semiconductors with proton beams. A review

Analysis is given of the progress in the modification of semiconductors by proton beams in fields such as proton-enhanced diffusion, ion-beam mixing, and formation of porous layers. This method of modification (doping) is shown to have high potential in monitoring the properties of semiconductor materials and designing devices of micro and nano electronics as compared to the conventional doping techniques such as thermal diffusion, epitaxy, and ion implantation.     

Fabricating the solution-processable inverted photovoltaic devices by the dip-coating method

All solution processable photovoltaic (PV) devices have been great interests in the past decade and different processing methods have been explored to produce the PV devices. In this paper, the dip-coating method was studied to fabricate core layers in the inverted polymer photovoltaic devices, which demonstrates that the dip-coating technology has its potential to produce large area PV devices. The crystallinity of the active layers by the dip-coating method can be improved under the condition of the extended drying rate. Light absorption spectra and X-ray diffraction (XRD) patterns of the active layers were investigated to confirm the improved crystallinity of the active layers. Various morphologies of the dip-coated layers were observed by the atomic force microscopy (AFM). The best PV device achieved ∼3.4% power conversion efficiency.     

Protection of InP EPI-ready wafers by controlled oxide growth

Epitaxy ready InP surfaces for MBE applications have been prepared by either thermal or photochemical oxidation. The composition and thickness of these oxide layers has been determined by XPS. Oval defect densities in GaInAs epitaxial layers have been correlated with the concentration of residual oxygen at the surface after thermal desorption prior to epitaxy. An optimized thermal pretreatment has been evaluated yielding defect free layers. The presence of carbon as a major source of contamination is discussed.     

Electrical and optical properties of lodine doped CdZnTe layers grown by metalorganic vapor phase epitaxy

Electrical and photoluminescence properties of iodine doped CdZnTe (CZT) layers grown by metalorganic vapor phase epitaxy have been studied. Doped layers showed an n-type conductivity from the Zn composition x=0 (CdTe) to 0.07. Above x=0.07, resistivities of doped layers increased steeply up to 10⁶ Ω-cm. Resistivities of doped CZT layers were higher than those of undoped layers above x=0.6. Photoluminescence intensity of doped layers increased compared to undoped layers. Doped CdTe and ZnTe layers showed neutral donor bound exciton emission lines at the exciton related region. Also, these layers showed an increase in emission intensity at the donor acceptor pair recombination bands. Sharp emission lines were observed in doped CZT layers at around 1.49 eV. These emission lines were considered to be originated from GaAs substrates which were optically excited by the intense emission from doped CZT layers.     

Noise investigation of ultraviolet laser induced grain structure in polyimide films

The ultraviolet laser treatment of polyimide films can lead to the formation of conductive area. The conductive layers show a carbon-rich grain structure. The heat treatment was carried out in air and nitrogen atmosphere. Morphology of conductive layers was investigated by scanning electron microscopy and transmission electron microscopy. On laser induced conductive layer, electrical noise investigation was carried out. Our investigation shows that laser induced layers have 1/f noise spectra. According to our results, conductive layers prepared in nitrogen atmosphere have better stability than those prepared in air.