Light-splitting photovoltaic system utilizing two dual-junction solar cells

There are many difficulties limiting the further development of monolithic multi-junction solar cells, such as the growth of lattice-mismatched material and the current matching constraint. As an alternative approach, the light-splitting photovoltaic system is investigated intensively in different aspects, including the energy loss mechanism and the choice of energy bandgaps of solar cells. Based on the investigation, a two-dual junction system has been implemented employing lattice-matched GaInP/GaAs and InGaAsP/InGaAs cells grown epitaxially on GaAs and InP substrates, respectively.     

Diffuse diffracted features and ordered domain structures in GalnP layers grown by organometallic vapor phase epitaxy

Transmission electron diffraction (TED) and transmission electron microscope (TEM) studies have been made of organometallic vapor phase epitaxial Ga_xIn_1−xP layers (x ≈ 0.5) grown at temperatures in the range 570–690°C to investigate ordering and ordered domain structures. TED and TEM examination shows that the size and morphology of ordered domains depend on the growth temperature. The ordered domains change from a fine rod-like shape to a plate-like shape as the growth temperature increases. The domains are of width 0.6∼2 nm and of length 1∼10 nm. Characteristic diffuse features observed in TED patterns are found to depend on the growth temperature. Extensive computer simulations show a direct correlation between the ordered domain structures and such diffuse features. A possible model is suggested to describe the temperature dependence of the ordered domain structure.     

Growth characteristics of hydride-free chemical beam epitaxy and application to GaInP/GaAs heterojunction bipolar transistors

We report on the complete characterization of a hydride- and hydrogen-free chemical beam epitaxy (CBE) process for the realization of GaAs/GaInP heterojunction bipolar transistors. Alternative group V sources tertiarybutylarsine, tertiarybutylphosphine, and trisdimethylaminoarsenic are used instead of traditionally employed AsH₃ and PH₃. A very high degree of reproducibility of growth parameters (fluxes, substrate temperature, doping levels) is demonstrated. Total defect densities lower than 10 def/cm² are routinely obtained. Large-area GaInP/GaAs heterojunction bipolar transistors (HBTs) show a high current gain of 225 for base sheet resistance of 400 ohm/sq. The devices also exhibit excellent high-frequency characteristics. A cut-off frequency of 48 GHz and a maximum oscillation frequency of 60 GHz have been obtained. These results demonstrate the high potential capability of CBE for high-throughput GaInP/GaAs HBT production.     

Control of ordering in GaInP and effect on bandgap energy

Ga_xIn_1-x P layers with x ≈ 0.5 have been grown by atmospheric pressure organometallic vapor phase epitaxy on GaAs substrates with 10 micron wide, [110]-oriented grooves produced photolithographically on the surface. The [110] steps and the misorientation produced at the edges of the grooves have been found to have important effects on the formation of the Cu-Pt ordered structure (ordering on {111} planes) in the GaInP layers during growth. In this work, the groove shape is demonstrated to be critically important. For the optimum groove shape, with a maximum angle to the (001) surface of between 10 and 16°, single domains of the (-111) and (1-11) variants of the Cu-Pt ordered structure are formed on the two sides of the groove. Shallow (≤0.25 μm deep) grooves, with maximum angles of <10°, are less effective. Within the large domains on each side of the groove, small domains of the other variant are observed. The boundary between the two domains is seen to wander laterally by a micron or more during growth, due to the change in shape of the groove during growth. For deep (1.5 μm) grooves, with maximum angles to the (001) plane of 35°, only a single variant is formed on each side of the groove. However, the domains are small, dispersed in a disordered matrix. For substrates with deep grooves on a GaAs substrate misoriented by 9° toward the [-110] direction, an interesting and useful pattern is produced. One half of the groove is a single domain which shrinks in size as the growth proceeds. The other half of the groove, where the misorientation is larger, is disordered. Thus, every groove contains large (>1 μm² cross-sectional area and several mm long) regions of highly ordered and completely disordered material separated by no more than a few microns. This allows a direct determination of the effect of ordering on the bandgap of the material using cathodoluminescence (CL) spectroscopy. The 10K photoluminescence (PL) consists of three distinct peaks at 1.94, 1.88, and 1.84 eV. High resolution CL images reveal that the peaks come from different regions of the sample. The high energy peak comes from the disordered material and the low energy peak comes from the large ordered domains. Electron microprobe measurements of the solid composition demonstrate that the shift in emission energy is not due to changes in solid composition. This is the firstdirect verification that ordering causes a reduction in bandgap of any III/V alloy. Decreasing the Ga_0.5In_0.5P growth rate from the normal 2.0 to 0.5 μ/h is found to enhance ordering in layers grown on planar GaAs substrates. Transmission electron diffraction results show that the domain size also increases significantly. For material grown on exactly (001)-oriented substrates, a pronounced [001] streaking of the superlattice spots is observed. This is correlated with the presence of a dense pattern of fine lines lying in the (001) plane in the transmission electron micrographs. The PL of this highly ordered material consists of a single peak that shifts to higher energy by > 110 meV as the excitation intensity is increased by several orders of magnitude.     

Thermal analysis of multi‐finger GaInP collector‐up heterojunction bipolar transistors with miniature heat‐dissipation packaging structures

We build up a finite element modeling (FEM) approach to analyze the thermal performance of collector‐up (C‐up) heterojunction bipolar transistor (HBTs) with a heat‐dissipation via configuration. Highly compact heat‐dissipation packaging structures of GaInP/GaAs C‐up HBTs have been designed and evaluated systematically. In this work, we devise the 2‐D and 3‐D models to simulate the actual devices and to investigate the temperature distribution behavior. Results from 2‐D model indicate that the large heat‐dissipation via configuration can be further reduced by 29% to meet the requirement of HBT‐based small high‐power amplifiers (HPAs) for the cellular phones. Furthermore, the demonstrated results show that the maximum temperature within the collector calculated from 3‐D model is lower than that from 2‐D model. In the 3‐D analysis, it is revealed that the configuration can be reduced by 32%. Therefore, thinning the heat‐dissipation via constructed underneath the GaInP/GaAs C‐up HBT should be helpful for miniaturization of HBT‐based HPAs in future mobile communication systems. Copyright © 2009 John Wiley & Sons, Ltd.     

界面复合效应对 Ⅲ-Ⅴ族叠层太阳电池性能的影响研究

界面复合是影响串联叠层太阳能电池效率的主要因素之一,详细分析和计算界面复合效应对理解光伏器件的性能是必要的.本文给出一个典型的GaInP/GaInAs/Ge 叠层太阳电池结构,在AM0辐照光谱工作条件下,通过包括光学和电学模块的理论模型计算了三个子电池正面、背面复合速率对叠层电池电流-电压特性曲线的影响.研究表明,GaInP顶电池界面复合是获得高效率叠层太阳能电池的主要限制因素。     

国产高效GaInP/GaAs/Ge三结太阳电池的低能质子辐射效应

运用2×1.7MV串列静电加速器提供的质子束,对MOCVD方法制备的GaInP/GaAs/Ge三结电池进行低能质子辐射效应研究.选质子能量为0.28,0.62和2.80MeV,辐照注量为1×1010,1×1011,1×1012和1×1013cm-2.对电池的辐射效应用I-V特性和光谱响应测试进行分析.研究结果表明:随辐照注量的增加,太阳电池性能参数Lsc,Voc和Pmax的衰降幅度均增大;但随质子辐照能量的增加,Lsc,Voc和Pmax的衰降幅度均减小.实验中0.28MeV质子辐照引起电池Lsc,Voc,Pmax衰降最显著,三结电池中光谱响应衰降最明显的是中间GaAs电池.     

Strain induced lateral ordering in Ga0.22In0.78As/Ga0.22In0.78P short period superlattices on (001) InP

The application of the strain induced lateral ordering process to the strain-compensated (Ga_0.22In_0.78As)_m (Ga_0.22In_0.78P)_m short period superlattices is investigated. The superlattices have been grown at low temperatures by solid source molecular beam epitaxy (MBE) on (001) InP. These superlattices have been used in multiquantum well heterostructures using InP as barriers. The anisotropic polarization of photoluminescence shows the existence of lateral modulation. Dark-field images using the 220 reflection gives modulated contrast in the superlattice layers. High-resolution transmission electron microscopy shows local variations of the interplanar spacing of the (200) planes as well as the angles they form with the (002) planes.