Photocurrent anisotropy in compositional modulated superlattice of long-range ordered Ga0.5In0.5P

Photocurrent anisotropy of long-range ordered Ga_0.5In_0.5P alloys has been sys-tematically investigated. The ordered Ga_0.5In_0.5P is a compositional modulated superlattice of Ga_0.5+η/2In_0.5-η/2P and Ga_0.5-η/2In_0.5+η/2P monolayer planes, where η is a long-range order parameter. The photocurrent edge of the [110] polarization is lower than that of the . The observed anisotropy in the photocurrent spectra is due to a crystal-field splitting at the valence-band maximum in ordered Ga_0.5In_0.5P. The anisotropy shows a continous variation as a function of η. In order to make clear the effects of the valence-band splitting on the polarized photocurrent spectra, we performed theoretical calculations in which a distribu-tion of η in the epitaxial film and an order-parameter dependence of oscillator strength were considered. From these calculations, it is found that oscillator strength is a key parameter in the anisotropic character. The calculated results moderately agree with the measured data. Furthermore, the epitaxial thickness dependence of the anisotropic character in photocurrent was investigated.     

Determination of ordering induced birefringence in (Al)GaInP

In this paper, the first measurement of the ordering induced birefringence in GaInP and (Al_0.33Ga_0.67)InP is presented. It is found that these ordered crystals are positively birefringent far below the bandgap and become negatively birefringent at the bandgap. The method to measure the birefringence is based on the modifications introduced by ordering to the mode structure of planar waveguides. The change of the sign of birefringence at the bandgap is due to the highly anisotropic interband matrix element. The dispersion of the measured birefringence is in good agreement with six-band k·p calculations.     

GaInP气相外延中Si的掺杂行为及发光二极管材料的制备

用MOCVD方法生长GaInP及其掺杂材料，并对Si的掺杂行为进行了较详细的研究。采用低温度冲层技术可有效地控制高温（＞700℃）生长GaInP及其掺杂材料的组分，从而使得GaInP掺Si的电子浓度达8×1018cm－3。在此基础上，进行了GaInP发光二极管材料的生长，所得器件具有良好的I－V曲线。     

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.     

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.     

MOVPE grown Ga1−xInxAs solar cells for GaInP/GaInAs tandem applications

Lattice-mismatched Ga_1−xIn_xAs solar cells with an absorption edge between 900 and 1150 nm have been grown on GaAs substrates. Different graded Ga_1−xIn_xAs buffer layers and solar cell structures were evaluated to achieve a good electrical performance of the device. External quantum efficiencies comparable to our best GaAs solar cells were measured. The best 1 cm² cell with a bandgap energy of 1.18 eV has an efficiency of 22.6% at AM1.5g and a short circuit current density of 36.4 mA/cm². To our knowledge, this is the highest reported efficiency for a Ga_0.83In_0.17As solar cell.     

Theoretical modeling of the interface recombination effect on the performance of Ⅲ-Ⅴtandem solar cells

A typical GaInP/GaInAs/Ge tandem solar cell structure operating under AM0 illumination is proposed, and the current-voltage curves are calculated for different recombination velocities at both front and back-surfaces of the three subcells by using a theoretical model including optical and electrical modules. It is found that the surface recombination at the top GaInP cell is the main limitation for obtaining high efficiency tandem solar cells.     

MOCVD制备的ZnO薄膜及其在太阳电池背电极应用

研究了利用LP-MOCVD技术制备的不同B掺杂浓度对ZnO薄膜的微观结构和光电特性影响.对XRD和SEM的研究结果表明,B掺杂对ZnO薄膜的微观结构有重大影响.通过优化工艺,当B2H6流量为17sccm(约1%掺杂浓度)时,在20cm×20cm大面积衬底上生长出厚度为700nm,方块电阻为38Ω/□,透过率大于85%,迁移率为17.8cm2/(V·s)的绒面结构ZnO薄膜.其应用于太阳电池背反射电池后,可使电池短路电流提高将近3mA,使20cm×20cm面积的a-Si集成电池效率高达9.09%.     

MOCVD制备的ZnO薄膜及其在太阳电池背电极应用

研究了利用LP-MOCVD技术制备的不同B掺杂浓度对ZnO薄膜的微观结构和光电特性影响.对XRD和SEM的研究结果表明,B掺杂对ZnO薄膜的微观结构有重大影响.通过优化工艺,当B2H6流量为17sccm(约1%掺杂浓度)时,在20cm×20cm大面积衬底上生长出厚度为700nm,方块电阻为38Ω/□,透过率大于85%,迁移率为17.8cm2/(V·s)的绒面结构ZnO薄膜.其应用于太阳电池背反射电池后,可使电池短路电流提高将近3mA,使20cm×20cm面积的a-Si集成电池效率高达9.09%.     

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。     

Optimization of Multi-layer AR Coatings for GaInP／GaAs Tandem Solar Cells

The AR coatings for GaInP/GaAs tandem solar cell are simulated. Results show that, under the condition of the lack of suitable encapsulation, a very low energy loss could be reached on MgF2/ZnS system;in the case of glass encapsulation,the Al2O3/ZrO2 and Al2O3/TiO2 systems are appropriate choice; for AlInP window layer,the thickness of 30nm is suitable.     

GaInP/GaAs/Ge叠层太阳电池的研制及其温度依赖性分析

利用MOCVD方法制备了GaInP/GaAs/Ge叠层太阳电池。测试了I-V特性,并测试分析了该电池性能在30℃至170℃温度范围内的变化情况。测试结果表明,随着温度的升高,短路电流密度略微增大,温度系数为9.8 (μA/cm2)/℃;开路电压以系数-5.6mV/℃急剧下降;填充因子也随之下降（-0.00063 /℃）;电池的转换效率随温度升高线性减小,温度从30℃升高至 130℃时,效率从28%下降至22.1%。最后,本文对该叠层电池随着温度变化的特性给予了详细的理论分析。     

Growth of direct bandgap GalnP quantum dots on GaP substrates

GaInP has a direct bandgap for In concentrations higher than approximately 30%, and the band-lineup between GaInP and GaP is type-II for In concentrations less than 60%. Therefore, in order to use GaInP as the active light-emitting layer in an optoelectronic device grown on GaP, the strain induced by the lattice mismatch between GaInP and GaP has to be somehow managed such that formation of crystal defects is suppressed. One method is to grow the layer thinner than the critical thickness. Another method that recently received much attention is to grow strain-induced Stranski-Krastanov islands (sometimes referred to as self-assembled quantum dots). Small droplets of highly latticmismatched materials have been embedded into single crystals without generating defects such as threading dislocations and stacking faults using this method. We have grown a series of GaInP/GaP layers by metalorganic chemical vapor deposition and have studied the light emission from them. Ordered GaInP islands were found to be responsible for the light emission. We present the light emission characteristics of these ordered GaInP/GaP islands, and their dependence on various growth parameters.     

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.     

Localized deposition of GaAs/GaInP heterostructures using LP-MOVPE

GaInP layers were grown selectively by low pressure MOVPE in patterned SiO₂ masks on GaAs (100) substrates. The variation of the composition and spontaneous ordering phenomena were analysed by Raman spectroscopy and photoluminescence. In contrast to GaInAs, the composition of GalnP shows only a very weak dependence on the size of the structures. On the other hand, there is a shift of the bandgap energy up to 40 meV with decreasing size of the stripes caused by ordering of the Ga and In atoms. Based on these findings lattice matched GaAs/GalnP multilayers were grown to delineate the growth history of the structures. It was demonstrated that the growth habit of deposition in narrow slits (>1μm) can be used to produce mesa-like stripes with dimensions below 100 nm on top of the mesa. Results of GaAs/GaInP quantum wells selectively grown on top of a mesa are presented.     

Transmission electron microscopy study of the effect of selenium doping on the ordering of GalnP2

Selenium doped Ga_0.51In_0.49P films have been grown by metalorganic chemical vapour deposition at 600, 670 and 740° C. The extent of ordering of the Group III sublattice has been monitored by transmission electron microscopy. Ordering disappears at carrier concentrations on the order of 10¹⁸ cm⁻³ for samples grown at 600 and 740° C although a small degree of ordering persists in the samples grown at 670° C up to a carrier concentration of 10¹⁹ cm⁻³. At each growth temperature, the ordering observed decreased and the bandgap measured increased with increasing Se doping.