Microcrystalline silicon films and tandem solar cells prepared by triode PECVD

This paper investigates the effects of the diphasic structure on the optoelectronic properties of hydrogenated microcrystalline silicon (mu c-Si:H) films prepared in a triode three-chamber plasma-enhanced chemical vapor deposition (PECVD) system. The influences of boron-compensation doping on the dark-and photo-conductivity of mu c-Si:H films are also described. A tandem solar cell with an entirely mu c-Si:H p-i-n bottom cell and an a-Si:H top cell has been prepared with an initial conversion efficiency of 8.91% (0.126 cm(2), AM1.5, 100 mW/cm(2)).

Photodilatation effect of undoped a-Si:H films

A photodilatation effect of undoped a-Si:H films has been discovered by a differential dilatometric method. The film thickness has been found to increase instantaneously when the sample is exposed to light. The dilatation weakens with illumination time, following a stretched exponential law, and finally reaches a saturation value. The dilatation disappears when light is off. The results unambiguously show that the whole structure of the film becomes less compact and less stable under light exposure. The metastable change (Staebler-Wronski effect) could be a redistribution of different configurations after this photodilatation in the a-Si:H films.

Magnetospectroscopy of bound phonons in high purity GaAs

Far infrared magnetophotoconductivity performed on high purity GaAs reveals the existence of fine structures in the resonant magnetopolaron regions. The fine structures are attributed to the presence of bound phonons due to multiphonon processes. We demonstrate that the magnetopolaron energy spectrum consists of bound phonon branches and magnetopolaron branches. Our results also indicate that different phonons are bound to a single impurity, and that the bound phonon in Si-doped GaAs is a quasilocalized mode.

Improvement of the stability of hydrogenated amorphous silicon films by intermittent illumination treatment at elevated temperature

The intermittent illumination treatment by white light at elevated temperature is proved to be a convenient and efficient method for the improvement of the stability of hydrogenated amorphous silicon (a-Si:H) films. The effect of the treatment on electrical properties, light-induced degradation, and gap states of undoped a-Si:H films has been investigated in detail. With the increase of cycling number, the dark- as well as photo-conductivities in annealed state and light-soaked state approach each other, presenting an unique irreversible effect. The stabilization and ordering processes by the present treatment can not be achieved merely by annealing under the same conditions. It is shown that the treatment proposed here results in a shift to higher values of the energy barriers between defects and their precursors, and hence an improved stability of a-Si:H films. (C) 1996 American Institute of Physics.

A new structure of In-based ohmic contacts to n-type GaAs

Electrical, structural and reaction characteristics of In-based ohmic contacts to n-GaAs were studied. Attempts were made to form a low-band-gap interfacial phase of InGaAs to reduce the barrier height at the metal/semiconductor junction, thus yielding low-resistance, highly reliable contacts. The contacts were fabricated by e-beam sputtering Ni, NiIn and Ge targets on VPE-grown n(+)-GaAs film (approximate to 1 mu m, 2 x 10(18) cm(-3)) in ultrahigh vacuum as the structure of Ni(200 Angstrom)/NiIn(100 Angstrom)/Ge(40 Angstrom)/n(+)-GaAs/SI-GaAs, followed by rapid thermal annealing at various temperatures (500-900 degrees C). In this structure, a very thin layer of Ge was employed to play the role of heavily doping donors and diffusion limiters between In and the GaAs substrate. Indium was deposited by sputtering NiIn alloy instead of pure In in order to ensure In atoms to be distributed uniformly in the substrate; nickel was chosen to consume the excess indium and form a high-temperature alloy of Ni3In. The lowest specific contact resistivity (rho(c)) of (1.5 +/- 0.5)x 10(-6) cm(2) measured by the Transmission Line Method (TLM) was obtained after annealing at 700 degrees C for 10 s. Auger sputtering depth profile and Transmission Electron Microscopy (TEM) were used to analyze the interfacial microstructure. By correlating the interfacial microstructure to the electronical properties, InxGa1-xAs phases with a large fractional area grown epitaxially on GaAs were found to be essential for reduction of the contact resistance.

An asymmetric broad waveguide structure for a 0.98-μm high-conversion-efficiency diode laser

A novel asymmetric broad waveguide diode laser structure was designed for high power conversion efficiency (PCE). The internal quantum efficiency, the series resistance, and the thermal resistance were theoretically optimized. The series resistance and the thermal resistance were greatly decreased by optimizing the thickness of the P-waveguide and the P-cladding layers. The internal quantum efficiency was increased by introducing a novel strain-compensated GaAs_0.9P_0.1/InGaAs quantum well. Experimentally, a single 1-cm bar with 20% fill factor and 900 μm cavity length was mounted P-side down on a microchannel-cooled heatsink, and a peak PCE of 60% is obtained at 26.3-W continuous wave output power.The results prove that this novel asymmetric waveguide structure design is an efficient approach to improve the PCE.

用正电子研究原生ZnO单晶中的缺陷

利用正电子寿命谱和多普勒展宽谱技术研究了原生ZnO的缺陷结构及其退火效应. 经900 ℃退火之后,正电子寿命实验显示样品中的空位型缺陷基本被消除,其体寿命为180 ps.通过比较原生和退火样品的符合多普勒展宽谱的商谱曲线,两者有相似的峰型,结合寿命谱的相关数据表明原生ZnO中不存在H原子填充Zn空位.

掺Er／Pr的GaN薄膜深能级的研究

利用深能级瞬态谱（DLTS）、傅里叶变换红外光谱（FT-IR）对GaN以及GaN掺Er／Pr的样品进行了电学和光学特性分析．研究发现未掺杂的GaN样品只在导带下0．270eV处有一个深能级；GaN注入Er经900℃，30min退火后的样品出现了四个深能级，能级位置位于导带下0．300eV，0．188eV，0．600eV和0．410eV；GaN注入Pr经1050℃，30min退火后的样品同样出现了四个深能级。能级位置位于导带下0．280eV，0．190eV，0．610eV和0．390eV；对每一个深能级的来源进行了讨论．光谱研究表明，掺Er的GaN样品经900℃，30min退火后，可以观察到Er的1538nm处的发光。而且对能量输运和发光过程进行了讨论．

带有Bragg反射镜的谐振腔增强型Si光电探测器

采用电子束蒸发和键合技术，制作了具有高反射率的、表面为薄层单晶Si的分布Bragg反射器。用标准光刻工艺在单晶Si薄层上制作出窄带谐振腔增强型（RCE）金属一半导体一金属（MSM）光电探测器，响应峰值波长分别在836、900、965和1030nm处，其中在900nm处峰值半高宽为18nm。该器件具有波长选择特性，可有效抑制相邻频道间的串扰，而且容易制成集成面阵。

大功率GaInP／AlGaInP半导体激光器

制备了大功率实折射率GaInP／AlGaInP压应变分别限制量子阱激光器．所用外延材料在15°偏角的GaAs衬底上由有机金属气相外延一次外延生长得到．制备的激光器具有双沟脊波导结构，条宽和腔长分别为3和900μm，前后端面分别蒸镀5％的增透膜和95％的高反膜．分析了室温连续激射时激光器的光电输出性能．阈值电流的典型值为32mA，光学灾变阈值为88mW，功率为80mW时的工作电流为110mA，斜率效率为1W／A，串联电阻为3Ω．基横模光输出功率可达60mW，60mW时的平行结和垂直结的远场发散角分别为10°和32°，激射波长为658．4nm．器件的内损耗为4．1cm^-1，内量子效率达80％，透明电流密度为648A／cm^2．

1.78 μm Strained InGaAs-InGaAsP-InP Distributed Feedback Quantum Well Lasers

Ridge-waveguide distributed-feedback(DFB) lasers with highly strained InGaAs/InGaAsP active regions,emitting at 1.78 μm were fabricated by low pressure metal-organic vapor phase epitaxy(LP-MOVPE) and tested.The lasers exhibited threshold current of 33 mA for 900 μm long cavities at room temperature.A maximum light output power of 8 mW from one facet and an external differential quantum efficiency of 7% were also obtained.In oddition,the side mode suppression ratio (SMSR) is 27.5 dB.

掺铒GaN薄膜的背散射/沟道分析和光致发光研究

采用背散射(RBS)/沟道(channeling)分析和傅里叶变换红外光谱(FT-IR)研究了掺铒GaN薄膜的晶体结构和光致发光(PL)特性.背散射/沟道分析结果表明:随退火温度的升高,薄膜中辐照损伤减少;但当退火温度达到1000℃,薄膜中的缺陷又明显增加.Er浓度随注入深度呈现高斯分布.通过沿GaN的<0001>轴方向的沟道分析,对于900℃,30min退火的GaN:Er样品,Er在晶格中的替位率约76%.光谱研究表明:随退火温度的升高,室温下样品的红外PL峰强度增加;但是当退火温度达到1000℃,样品的PL峰强度明显下降;测量温度从15K变化到300K时,样品(900℃,30min退火的GaN:Er)的1540nm处PL温度猝灭为30%.

紧缩型SOI多模干涉光开关的设计

提出了一种新的紧缩型SOI多模干涉（MMI）光开关。开关由单模输入输出波导和MMI耦合器组成。通过在多模波导区域引入调制区，利用Si的等离子色散效应（PDE）改变调制区的折射率来实现开关动作。用FD-BPM方法对开关的工作原理和性能进行了模拟与分析。结果表明，光开尖良好的综合性能，而整个开关的长度只有7mm。