Electron irradiation and thermal annealing effect on GaAs solar cells

This paper describes the effect of electron irradiation and thermal annealing on LPE AlGaAs/GaAs heterojunction solar cells with various p/n junction depths. The electron irradiation experiments were performed with energy of 3 MeV, fluences ranging from 1 x 10(14) to 5 x 10(15) e/cm(2). The results obtained demonstrate that the irradiation-induced degradation of performances of the cells is mainly in the short circuit current and could be mostly recovered by annealing at 260 degrees C for 30 min. Four electron traps, E-c - 0.24 eV, E-c - 0.41 eV, E-c - 0.51 eV, E-c - 0.59 eV, were found by DLTS analysis, only two shallow levels of which could be removed by the annealing. (C) 1998 Elsevier Science B.V. All rights reserved.

Growth of GaSb and GaInAsSb layers for thermophotovolatic cells by liquid phase epitaxy - art. no. 68411E

GaSb based cells as receivers in thermophotovoltaic system have attracted great interest and been extensively studied in the recent 15 years. Although nowadays the manufacturing technologies have made a great progress, there are still some details need to make a further study. In this paper, undoped and doped GaSb layers were grown on n-GaSb (100) substrates from both Ga-rich and Sb-rich solutions using liquid phase epitaxy (LPE) technique. The nominal segregation coefficients k of intentional doped Zn were 1.4 and 8.8 determined from the two kinds of GaSb epitaxial layers. Additionally, compared with growing from Ga-rich solutions, the growing processes from Sb-rich solutions were much easier to control and the surface morphologies of epitaxial layers were smoother. Further-more, in order to broaden the absorbing edge, Ga1-xInxAsySb1-y quaternary alloys were grown on both GaSb and InAs substrates from In-rich solutions, under different temperature respectively.

Homoepitaxial growth of 4H-SiC multi-epilayers and its application to UV detection

Homoepitaxial growth of 4H-SiC p(+)/pi/n(-) multi-epilayer on n(+) substrate and in-situ doping of p(+) and pi-epilayer have been achieved in the LPCVD system with SiH4+C2H4+H-2. The surface morphologies, homogeneities and doping concentrations of the n(-)-single-epilayers and the p(+)/pi/n(-) multi-epilayers were investigated by Nomarski, AFM, Raman and SIMS, respectively. AFM and Raman investigation showed that both single- and,multi-epilayers have good surface morphologies and homogeneities, and the SIMS analyses indicated the boron concentration in p+ layer was at least 100 times higher than that in pi layer. The UV photodetectors fabricated on 4H-SiC p(+)/pi/n(-) multi-epilayers showed low dark current and high detectivity in the UV range.

Heavily doped polycrystalline 3C-SiC growth on SiO2/Si(100) substrates for resonator applications

3C-SiC is a promising material for the development of microelectromechanical systems (MEMS) applications in harsh environments. This paper presents the LPCVD growth of heavily nitrogen doped polycrystalline 3C-SiC films on Si wafers with 2.0 mu m-thick silicon dioxide (SiO2) films for resonator applications. The growth has been performed via chemical vapor deposition using SiH4 and C2H4 precursor gases with carrier gas of H-2 in a newly developed vertical CVD chamber. NH3 was used as n-type dopant. 3C-SiC films were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and room temperature Hall Effect measurements. It was shown that there is no voids at the interface between 3C-SiC and SiO2. Undoped 3C-SiC films show n-type conduction with resisitivity, Hall mobility, and carrier concentration at room temperature of about 0.56 Omega center dot cm, 54 cm(2)/Vs, and 2.0x 10(17) cm(-3), respectively. The heavily nitrogen doped polycrystalline 3C-SiC with the resisitivity of less than 10(-3) Omega center dot cm was obtained by in-situ doping. Polycrystalline SiC resonators have been fabricated preliminarily on these heavily doped SiC films with thickness of about 2 mu m. Resonant frequency of 49.1 KHz was obtained under atmospheric pressure.

Micro-raman investigation of defects in a 4H-SiC homoepilayer

Three types of defects, namely defect I, defect 11, defect 111, in the 4H-SiC homoepilayer were investigated by micro-raman scattering measurement. These defects all originate from a certain core and are composed of (1) a wavy tail region, (11) two long tails, the so called comet and (111) three plaits. It was found that there are 3C-SiC inclusions in the cores of defect 11 and defect III and the shape of inclusion determines the type of defect II or defect III. If the core contains a triangle-shaped inclusion, the defect III would be formed; otherwise, the defect 11 was formed. No inclusion was observed in the core of the defect I. The mechanisms of these defects are discussed.

Micro-fabricated Al0.3Ga0.7As pyramids for potential SPM applications

A novel technique of manufacturing Al0.3Ga0.7As pyramids by liquid phase epitaxy (LPE) for scanning probe microscopy (SPM) sensors is reported Four meticulously designed conditions-partial oxidation, deficient solute, air quenching and germanium doping result in defect-free homogeneous nucleation and subsequent pyramid formation. Micrometer-sized frustums and pyramids are detected by scanning electron microscopy (SEM). The sharp end of the microtip has a radius of curvature smaller than 50 nm. It is believed that such accomplishments would contribute not only to crystal growth theory, but also to miniature fabrication technology.

LIQUID-PHASE EPITAXY GROWTH AND PROPERTIES OF GAINASSB/ALGAASSB/GASB HETEROSTRUCTURES

The GaInAsSb/AlGaAsSb/GaSb heterostructures were grown by the liquid phase epitaxy (LPE) technique. The materials were characterized by means of optical microscopy, electroprobe microanalysis (EPMA), double-crystal X-ray diffraction, capacitance-voltage (C-V) and Van der Pauw measurments, infrared absorption spectra, photoluminescence and laser Raman scattering. The results show that the materials have fine surface morphology, low lattice mismatch and good homogeneity. Room-temperature light-emitting diodes with an emission wavelength of 2.2-mu-m were obtained by using the GaInAsSb/AlGaAsSb DH structures.

High efficiency AlxGa1-xAs/GaAs solar cells: Fabrication, irradiation and annealing effect

High efficiency AlxGa1-xAs/GaAs heteroface solar cells have been fabricated by an improved multi-wafer squeezing graphite boat liquid phase epitaxy (LPE) technique, which enables simultaneous growth of twenty 2.3 X 2.3cm(2) epilayers in one run. A total area conversion efficiency of 17.33% is exhibited (1sun, AM0, 2.0 x 2.0cm(2)). The shallow junction cell shows more resistance to 1 MeV electron radiation than the deep one. After isochronal or isothermal annealing the density and the number of deep level traps induced by irradiation are reduced effectively for the solar cells with deep junction and bombardment under high electron fluences.

Structure and device characteristics of AlxGa1-xAs/GaAs solar cells

AlGa1-xAs/GaAs heterostructures have been grown by two different liquid phase epitaxy (LPE) modes, i.e. the supercooled and melt-etch methods, for the fabrication of highly efficient solar cells. Typical structural characteristics observed under a transmission electron microscope (TEM), an Auger energy spectrometer (AES) and corresponding device parameters were presented. The results indicated that the P+PNN+ configuration grown by the melt-etch method could be used to produce high performance, large area solar cells with effectively reducing the defects of the substrate and improving the minority carrier collection by forming a compositionally graded region in the window layer.

高纯外延GaAs中浅施主杂质的光热电离谱研究

利用光热电离谱技术研究了4.5K下高纯n-GaAs外延材料的远红外光电导响应谱。给出CPE法和VPE法生长的高纯GaAs材料残留浅施主杂质分别是S、Sn和Sn、P等杂质。实验结果表明本所高纯GaAs组采用的LPE生长技术能有效抑制杂质Si和Sn的沾污。

1.27μm吸收型部分增益耦合MQW-DFB激光器

采用LP-MOCVD和LPE相结合,成功地研制出了吸收型部分增益耦合MQW-DFB激光器。扫描显微镜照片显示了清晰的被掩埋的吸收型增益耦合光栅,表明光栅掩埋生长前升温过程磷烷的保护是成功的。宽接触(broad area)脉冲电流大范围单纵模工作,条型器件室温连续直流工作阈电流为22mA至35mA,单模成品率高,边模抑制比(SMSR)超过37dB,没有观察到饱和吸收现象。

InGaAs/GaAs应变层量子阱激光器深中心行为

应用深能级瞬态谱(DLTS)技术研究分子束外延(MBE)和二次液相外延(LPE)生长的InGaAs/GaAs应变层量子阱激光器深中心行为,在MBE激光器的n-Al_xGa_(1-x)As组分缓变层和限制层里,除众所周知的DX中心外,还观察到有较大俘获截面的深(空穴、电子)陷阱及其相互转化.这些陷阱可能分布在x从0到0.40和x=0.40的n-Al_xGa_(1-x)As层里x值不连续的界面附近.而在LPE激光器的n-Al_xGa_(1-x)As组分缓变层和限制层里,DX中心浓度明显减少,且深(空穴、电子)陷阱消失,这表明LPE掩埋结构工艺可能对激光器深中心的消除或减少有一定作用.深中心的变化与样品阈值电流密度的改善是相符的.

InP-based optoelectronic devices for optical fiber communications

In this contribution we report the research and development of 1.55 mu m InGaAsP/InP gain-coupled DFB laser with an improved injection-carrier induced grating and of high performance 1.3 mu m and 1.55 mu m InGaAsP/InP FP and DFB lasers for communications. Long wavelength strained MQW laser diodes with a very low threshold current (7-10 mA) have been fabricated. Low pressure MOVPE technology has been employed for the preparation of the layered structure. A novel gain-coupled DFB laser structure with an improved injection-carrier modulated grating has been proposed and fabricated. The laser structures have been prepared by hybrid growth of MOVPE and LPE techniques and reasonably good characteristics have been achieved for resultant lasers. High performance 1.3 mu m and 1.55 mu m InGaAsP/InP DFB lasers have successfully been developed for CATV and trunk line optical fiber communication.

海洋动植物中不饱和脂肪酸的研究

不饱和脂肪酯是人及动物生长发育的必需物质。本论文分析了海洋动植物脂和脂肪酸的组成，并对不饱和脂肪酸的分离提纯方法进行了研究。一、海洋动植物的中性脂主要包括三酰甘油和胆固醇。动物极性脂主要为磷脂，包括磷脂酰丝馆酸（PS）、磷脂酸（PA）、磷脂酰肌醇（PI）、溶解性磷脂酰乙醇胺（LPE）、神经鞘磷脂（CAEP）、磷脂酰胆碱（PC）、磷脂酰乙醇胺（PE），双磷脂酰甘油（DPG）。其中LPE、DPG为动物所特有的磷脂。植物极性脂包括PI、PC、PE、双半乳糖苷地酰甘油酯（DGDG）、硫代6-脱氧葡萄糖苷二酰甘油酯（SQDG）、单半乳糖苷二酰甘油酯（MGDG）、磷脂酰甘油（PG）及植物脑苷脂（Plant Cerebrosides）。其中MGDG、DGDG、SQDG为植物所特有的三种糖脂。二、海洋动植物含有丰富的不饱和脂肪酸，多聚不饱和脂肪酸（PUFA）含量尤为显著。灰凹贻贝（Crenomythilus graiaynus）的二十碳五烯酸（EPA）含量为10.6%,二十碳四烯酸（AA）为3.7%，二十二碳六烯酸（DHA）为14.26%。中间球海胆（Strongylocentrotus intermedius）的AA含量为7.36%，EPA为15.98%。内枝多管藻（Polysiphonia morroωii)PUFA含量非常高，AA占2.43%，20:4ω3占4.97%，EPA占45.03%。裙带菜（Undaria pinnatifida）的PUFA中，十八碳二烯酸占6.16%，AA占12.99%，EPA占7.83%这些PUFA大都为人及动物生长发育的必需脂肪酸。三、尿素诱导法是大量提取混合PUFA的有效方法。在产品中，饱和脂肪酸的含量可以忽略不计，单烯脂肪酸含量降低很多；高吸附能力的柱层析是提取PUFA单体的较好方法，其产物的纯度达98%以上。