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1.
Chen J.J. Gao G.-B. Chyi J.-I. Morkoc H. 《Electron Devices, IEEE Transactions on》1989,36(10):2165-2172
Avalanche breakdown behavior at the collector junction of the GaAs/AlGaAs HBT (heterojunction bipolar transistor) has been studied. Junction breakdown characteristics displaying hard breakdown, soft breakdown, and negative resistance breakdown behavior were observed and are interpreted by analysis of localized microplasma effects, uniform microplasma-free behavior, and associated current gain measurements. Light emission from the collector-base junction of the GaAs/AlGaAs HBT was observed and used to investigate breakdown uniformity. Using a simple punchthrough breakdown model, the theoretical breakdown curves at different collector doping concentrations and thicknesses were computed and found to be in agreement with maximum breakdown voltages measured from devices displaying the most uniform junction breakdown. The serious current gain degradation of GaAs/AlGaAs HBTs at low current densities was analyzed in connection with the measurement of a large collector-emitter breakdown voltage. The unexpected functional relationship between the collector-emitter breakdown voltage and collector-base breakdown voltage is explained by the absence of a hole-feedback effect for devices not exhibiting transistor action 相似文献
2.
Temperature-dependent current-voltage measurement was employed to study the band offsets of the In0.30Ga0.70As/In 0.29Al0.71As heterojunction. The conduction band discontinuity was determined to be 0.71±0.05 eV which corresponds to a conduction band offset to bandgap difference ratio ~0.66. The comparison between experimental and theoretical results is presented 相似文献
3.
本文介绍了电炉无渣出钢技术在国外的应用与发展现状,结合我国电炉的装备水平,重点讨论了应用虹吸出钢和偏心炉底出钢两种方法的条件、作用和应采取的措施。 相似文献
4.
Unsteady-state periodic operations can improve the optimal steady-state performance of nonlinear chemical processes. To examine if the optimal periodic operation is proper and to obtain the optimal forcing functions subject to various control and state constraints it is suggested in this paper to convert the problems into a form which is suitable for constrained nonlinear programming. The adopted numerical optimization method is based on employing the control parametrization technique and is thus capable of dealing with the problem of multiple input forcings and obtaining optimal forcing functions and/or parameters while subject to general constraints. Besides, it provides information about to what extent the process performance can be improved by adopting the optimal periodic control. 相似文献
5.
The reaction between silicon carbide and aluminium to form silicon and Al4C3 in SiC particle-reinforced aluminium fabricated by liquid aluminium infiltration was most severe near the original interface between liquid aluminium and the SiC preform. This resulted in the highest concentration of Al4C3 and the lowest concentrations of silicon and SiC in the part of the composite near this interface. In particular, the silicon concentration was highest in the bottom centre of the composite when infiltration occurred from the top, because silicon diffused toward the surrounding aluminium melt before solidification. These non-uniform phase distributions, as measured by X-ray diffraction and differential scanning calorimetry, did not cause any non-uniform shear strength distribution. However, excessive reaction between SiC and aluminium, as observed for an infiltration (=mould=liquid metal) temperature of 780° C, caused the tensile strength to decrease. In the case where a steel mould was used during infiltration at 780° C, iron-containing precipitates, such as ternary Al-Fe-Si, were observed in the part of the composite within 5 mm from the above-mentioned interface; their formation was related to the silicon out-diffusion in the form of liquid Al-Si; they caused the shear strength to be lower in this part of the composite; larger such precipitates (up to 100 m) were observed in the excess aluminium adjacent to the cast composite. For pure aluminium as the infiltrating metal, the optimum infiltration temperature for the highest tensile strength was 700° C. An infiltration temperature of 670° C resulted in incomplete infiltration, which was more severe when a steel mould rather than a graphite mould was used because of the higher thermal conductivity of the former. 相似文献
6.
Peng L.-H. Lai C.-M. Shih C.-W. Chuo C.-C. Chyi J.-I. 《IEEE journal of selected topics in quantum electronics》2003,9(3):708-715
We examine the issues of spontaneous and piezoelectric polarization discontinuity on the optical properties of 3.0-nm-thick indium gallium nitride (InGaN) multiple quantum wells (MQWs). A quench of band-edge emission from the cap GaN layer is observed when the photoexcitation source is changed from a 355- to a 248-nm laser. The interband transitions from the InGaN wells exhibit a linear dependence on the 1) spectral blue shift of /spl sim/8.5/spl times/10/sup -18/ meV /spl middot/ cm/sup 3/ and 2) change of the internal field of /spl sim/3/spl times/10/sup -14/ meV /spl middot/ cm/sup 2/ with the injected carrier density up to N/sub inj//spl sim/10/sup 19/ cm/sup -3/ at 77 K. These observations are attributed to the redistribution of photogenerated carriers in the InGaN wells due to the polarization discontinuity at the QW interface and the surface band bending effect. By incorporating an additional boundary condition of surface Fermi-level pinning into the Poisson equation and the band-structure analysis, it is shown the emission from the InGaN-GaN MQWs is dominant by the recombination between the high-lying subbands and the screening of internal field effects. 相似文献
7.
Chyi Hwang 《中国工程学刊》2013,36(6):647-656
Abstract A new mixed method using modified stability array and mean‐square error (MSE) criterion is proposed for deriving reduced‐order 2‐transfer functions for discrete‐time systems. More precisely, the modified Routh stability array is used to obtain the reduced‐order denominator, thus ensuring stability preservation, while the numerator is obtained by minimizing the mean‐square error between the unit step responses of the original system and reduced model. The main feature of the method is that it does not actually evaluate the system and model responses in the step of minimizing mean‐square error. 相似文献
8.
9.
介绍了一种聚丙烯酰胺粉末降尘技术。通过室内评定、工业化降尘应用试验和现场配注应用试验证明,该涂层剂具有很好的降低聚丙烯酰胺粉末扬尘效果。室内对照实验表明涂层后聚丙烯酰胺的抗剪切能力、耐盐能力和热稳定性均有一定程度的提高,说明涂层后的聚丙烯酰胺更适用于三次采油领域。涂层操作简便易行,利用聚丙烯酰胺生产现有工艺设备就可进行工业化生产。采用本降尘技术可在聚丙烯酰胺正常生产中和处理库存细粉中创巨大的经济效益和社会效益,同时,大大改善了生产装置和现场配制的粉尘问题,给生产和应用操作人员创造了更好的工作环境。 相似文献
10.
针对粉煤灰氨含量的测定研究大多考虑单一因素,而忽略了在浸提过程中各因素间的交互作用对粉煤灰氨含量浸提的影响。以浸提剂浓度(A)、固液比(B)、振荡时间(C)作为考察因素,在单因素实验的基础上进行响应面实验,建立回归模型。通过响应面优化确定最佳的浸提工艺并与现有浸提方法的测定结果进行对比。结果表明,影响因素主次顺序为B、A、C、AB、BC、AC。最佳浸提工艺条件:浸提剂浓度为0.125 mol/L、固液比(质量体积比,g/mL,以下简称固液比)为1∶12.8、振荡时间为22 s。通过验证,发现实测值与预测值仅存在-2%的相对误差。相较现有浸提方法,优化后的浸提方法不仅使浸提时间大幅缩短,还使浸出率增加了73%~91%,为粉煤灰中氨含量的准确测定提供了新的方法与思路。 相似文献