Studies of the Ga1-xInxAs1-ySby quaternary alloy system I. liquid-phase epitaxial growth and assessment

The liquid phase epitaxial (LPE) growth of Ga_1-xIn_xAs_1-ySb_y alloys lattice-matched to InAs and GaSb substrates has been investigated in the temperature range 520 to 600° C. Theoretical phase diagram calculations have been used to obtain good predictions of the liquid phase compositions required to obtain lattice-matched growth as a function of growth temperature. The relative merits of InAs and GaSb as substrates are discussed. The layers were assessed by single and double-crystal X-ray diffraction, electron beam microprobe analysis and photoresponse of electrolyte Schottky barriers. Good agreement between alloy composition(x, y) measured by microprobe analysis and that deduced from combined lattice parameter and band-gap measurements. The problem of compositional grading in thicker layers due to depletion of arsenic in the growth solution is discussed. To overcome this problem it is necessary to reduce the growth rate of the layer by reducing the cooling rate to ∼1° C hr^-1.     

Infrared reflectivity studies of gax in1-x asy p1-y quaternary compounds

Reflectivity spectra have been measured on Ga_xIn_1-xAS_yP_1-y quaternary alloys, lattice-matched to InP substrates, covering the complete composition range from y = 0 (InP) to y = 1 (Ga_0.47 In_0.53 As). The spectra have been analysed to obtain parameters of both the free carriers and lattice vibrations. The reflectivity method has been used to measure the carrier density and mobility, the relatively low mobilities obtained confirming the electrical measurements explained previously by the presence of strong alloy scattering in this system. Four phonon modes, corresponding to InAs-, GaAs-, InP- and GaP-like vibrations, were observed over most of the composition range, except for y ≲ 0.25 where the GaAs mode was not observed and the GaP mode was a weak mode within the reststrahlen band of the InP mode. Thus the behaviour of the system may be termed "two"-four mode. The oscillator strengths of the four modes are consistent with this behaviour and their variation may be explainable by assuming that Ga_xIn_1-xAS_yP_1-y is a random alloy.     

MOVPE growth of (Al, Ga)InP-based laser structures monitored by real-time reflectance anisotropy spectroscopy

Using a specially-designed spectrometer enabling combined reflectance anisotropy spectroscopy (RAS) and reflectance measurements on rotating substrates in a commercial MOVPE reactor, we report the first full-spectroscopic RAS-monitoring of (Al,Ga)InP-based 650 nm laser growth. First, a spectral database was built up from systematic studies of AlGaInP RAS signatures for different Al compositions, doping levels and growth temperatures. These data are subsequently used for the interpretation of characteristic RAS fingerprints taken throughout the entire laser growth process. From the analysis of characteristic changes in the RAS spectra even small deviations from the optimum process (doping levels, composition, etc.) which would effect the performance of the final device can be detected.     

MOVPE growth of (Al,Ga)InP-based laser structures monitored by real-time reflectance anisotropy spectroscopy

Using a specially-designed spectrometer enabling combined reflectance anisotropy spectroscopy (RAS) and reflectance measurements on rotating substrates in a commercial MOVPE reactor, we report the first full-spectroscopic RAS-monitoring of (Al,Ga)InP-based 650 nm laser growth. First, a spectral database was built up from systematic studies of AlGaInP RAS signatures for different Al compositions, doping levels and growth temperatures. These data are subsequently used for the interpretation of characteristic RAS fingerprints taken throughout the entire laser growth process. From the analysis of characteristic changes in the RAS spectra even small deviations from the optimum process (doping levels, composition, etc.) which would effect the performance of the final device can be detected. (This paper previously appeared in Vol. 29, No. 1, 2000, with Fig. 5 inadvertantly printed in black and white. It is reprinted here with Fig. 5 in color.)     

Evaluation of low-temperature interdiffusion coefficients in Hg-based superlattices by monitoring the E1 reflectance peak

We show that variations of the E₁ reflectance peak in Hg-based superlattices can be used to probe low-temperature interdiffusion by monitoring the shift of the E₁ peak with time over extended periods. Little evidence of interdiffusion was detected for a number of HgTe/CdTe and HgCdTe/CdTe superlattices stored at room temperature for approximately two years. Two HgTe/CdTe superlattices and one HgCdTe/CdTe superlattice were subsequently annealed in a dry nitrogen atmosphere at 100°C for approximately six months, and then at 150°C for 24 days. During these intervals, the superlattices were periodically removed from the anneal for reflectance measurements to assess the extent of the interdiffusion. Comparison of these results with calculations of superlattice bandgaps and interdiffusion profiles has led to an evaluation of the low temperature interdiffusion coefficients. These extend previous results to lower temperatures and confirm that the degradation of Hg-based superlattices devices due to thermal interdiffusion under normal processing, storage, and operating conditions should not be an issue of concern.     

Influence of alloy composition,substrate temperature,and doping concentration on electrical properties of Si-doped n-Alx Ga1−x As grown by molecular beam epitaxy

Capacitance and Hall effect measurements in the temperature range 10-300 K were performed to evaluate the deep and shallow level characteristics of Si-doped n-Al_xGa_-xAs layers with 0 × 0.4 grown by molecular beam epitaxy. For alloy compositions × 0.3 the overall trap concentration was found to be less than 10⁻² of the carrier concentration. In this composition range the transport properties of the ternary alloy are comparable to those of n-GaAs:Si except for lower electron mobibities due to alloy scattering. With higher Al content one dominant electron trap determines the overall electrical properties of the material, and in n-Al_0.35Ga_0.65As:Si the deep trap concentration is already of the order of the free-carrier concentration or even higher. For the composition × = 0.35 ± 0.02 the influence of growth temperature and of Si dopant flux intensity on the deep trap concentration, on shallow and deep level activation energy, and on carrier freeze-out behaviour was studied and analyzed in detail. Our admittance measurements clearly revealed that the previously assumed deepening of the shallow level in n-Al_x Ga_1-x As of alloy composition close to the direct-indirect cross-over point does actuallynot exist. In this composition range an increase of the Si dopant flux leads to a reduction of the thermal activation energy for electron emission from shallow levels due to a lowering of the emission barrier by the electric field of the impurities. The increasing doping flux also enhances the concentration of the dominant electron trap strongly, thus indicating a participation of the dopant atoms in the formation of deep donor-type (D,X) centers. These results are in excellent agreement with the model first proposed by Lang et al. for interpretation of deep electron traps in n-Al_x Ga_1-x grown by liquid phase epitaxy.     

C_(60)对DNA光动力学作用的FT-Raman光谱研究

采用傅里叶变换激光Ｒａｍａｎ光谱术从分子水平研究了富勒烯Ｃ６０对小牛胸腺ＤＮＡ的光动力学作用。结果表明光激发Ｃ６０对ＤＮＡ各组分基团均有不同程度的损伤，其中ＤＮＡ的空间构像破坏显著，腺嘌呤次之，骨架磷酸基团、脱氧核糖、嘧啶环等也遭到破坏并导致ＤＮＡ链断裂。这种结果并非由于Ｃ６０与ＤＮＡ分子之间直接的电子相互作用，而是通过单线态氧（１Ｏ２）或·ＯＨ，Ｏ２·－等多自由基作用所致     

用介电函数的三级微商谱精确确定GaxIn1—xP临界点的能量值

本文导出了弱电场则反射谱与电函数对能量的三级微商成正比。将ＭＯＣＶＤ方法生长的ＧａＩｎＰ以及掺Ｓｉ和掺Ｚｎ３个样品，用椭圆偏振光谱法测量得到了可见光区的介电函数谱，并求其三级微商谱，把用一分析电反射谱的三点法推广到分析介电函数的三级微商谱，得到弱电场调制反射谱的实验结果，并与介电函数谱的结果加以比较，使灵敏度和分辨率有很大提高。     

ZnO layers deposited by the ion layer gas reaction on Cu(In,Ga)(S,Se)2 thin film solar cell absorbers—impact of ‘damp‐heat’ conditions on the layer properties

Cu(In,Ga)(S,Se)₂ (‘CIGSSe’) based solar cells with a ZnO window extension layer (WEL) deposited by the ion layer gas reaction (ILGAR) reach competitive efficiencies compared to corresponding references with CdS buffer and lead to a simplified device structure. The WEL replaces not only the CdS buffer, but also the undoped part of the usually applied rf‐sputtered ZnO window bi‐layer. The long‐term stability of CIGSSe‐based solar modules is currently under investigation. In order to pass the respective stability tests, which include exposure to ‘damp‐heat’ (DH) conditions (85% relative humidity at 85(C) to accelerate possible aging effects, a good intrinsic material stability is required. In Reference¹ it was revealed, that ILGAR‐ZnO contains a certain amount of meta‐stable hydroxide, which can be directly tuned by the ILGAR process parameters (number of process cycles and process temperature). In order to determine the ILGAR process parameters, which result in intrinsically stable WELs, ILGAR‐ZnO/CIGSSe test structures were investigated by means of scanning electron microscopy (SEM) and x‐ray photoelectron spectroscopy (XPS) before and after a DH‐test. It was found that, induced by the DH‐conditions, a continuous dehydration of the WELs together with a disintegration of the ILGAR‐ZnO layers takes place. This supports an earlier suggested mechanism of a DH‐induced degradation by a release of water at the most critical location in a solar cell, at the heterointerface between window and absorber. By a systematic variation of the ILGAR process parameters it was possible to reduce the hydroxide content in the ILGAR‐ZnO layers resulting in intrinsically more stable samples. Copyright © 2006 John Wiley & Sons, Ltd.     

Impurities in hydride gases part 1: Investigation of trace moisture in the liquid and vapor phase of ultra-pure ammonia by FTIR spectroscopy

Trace moisture in ammonia is a critical impurity in the growth of epitaxial nitride films. Because moisture is very soluble in the liquid phase of ammonia, moisture in the vapor phase increases dramatically with cylinder use, and is often far higher than the nominal purity specification. A reliable method was developed for sampling and analyzing trace moisture in both liquid-and vaporphase ammonia using FTIR. Analysis of liquid-phase ammonia gives a stable and representative moisture value whereas gas-phase moisture levels strongly depend on sampling time, flow rate, temperature, mixing, and extent of cylinder use. The variation of vapor-phase moisture is discussed in terms of a variable vaporization model with applications to high flow.     

Single Molecular Wells–Dawson‐Like Heterometallic Cluster for the In Situ Functionalization of Ordered Mesoporous Carbon: A T 1‐ and T 2‐Weighted Dual‐Mode Magnetic Resonance Imaging Agent and Drug Delivery System

Developing a feasible way to prepare highly dispersed heterometallic nanoparticles incorporated in porous carbon composites is of significant importance for multifunctional materials. In this work, heterometallic γ‐Fe₂O₃ and GdPO₄ nanoparticles that are incorporated in ordered mesoporous carbon composites are facilely prepared by a one‐pot in situ method using a Wells–Dawson‐like cluster of [Fe₆Gd₆(μ₃‐O)₂(CO₃)(O₃PPh)₆(O₂C ^t Bu)₁₈] ({Fe₆Gd₆P₆} for short) as the precursor. It is verified that the γ‐Fe₂O₃ and GdPO₄ nanoparticles are highly dispersed and embedded into the carbon matrix with a particle size smaller than 5 nm, even when the carbon matrix is changed from 2D hexagonal P6mm to 3D body‐centered cubic Im‐3m symmetry. Additionally, a formation mechanism is proposed. Furthermore, dual‐mode magnetic resonance (MR) imaging and drug carrier properties are evaluated by in vitro experiments, which show a satisfactory T ₁‐ and T ₂‐weighted MR imaging effect with r ₁ and r ₂ relaxivity values of 2.7 and 183.7 mM^?1 s^?1, respectively, and doxorubicin hydrochloride carrier amount of 102 mg g^?1, identifying a combined function for potential diagnostic and therapy.     

应用GM(1,1)模型研究军用电子元器件的长期贮存寿命

现代武器装备“长期贮存,一次使用”的特性,要求装备的各个部件和元器件都具有良好的环境适应性与长期贮存寿命。根据灰色系统理论,以某电阻器为例,应用GM(1,1)模型及其改进模型预测了其长期贮存寿命,所建立的模型具有较好的精度,有一定的参考价值。实践证明：灰色预测方法简单、实用,具有一定的工程应用价值。     

Layer by layer characterisation of the degradation process in PCDTBT:PC71BM based normal architecture polymer solar cells

This work demonstrates the stability and degradation of OSCs based on poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′ benzothiadiazole)] (PCDTBT): (6,6)-Phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) photoactive blend layers as a function of ageing time in air. Analysis of the stability and degradation process for the OSCs was conducted under ambient air by using current-voltage (I-V) measurements and x-ray photoelectron spectroscopy (XPS). The interface between photoactive layer and HTL (PEDOT:PSS) was also investigated. Device stability was investigated by calculating decay in power conversion efficiency (PCE) as a function of ageing time in the air. The PCE of devices decrease from 5.17 to 3.61% in one week of fabrication, which is attributed to indium and oxygen migration into the PEDOT:PSS and PCDTBT:PC₇₁BM layer. Further, after aging for 1000 h, XPS spectra confirm the significant diffusion of oxygen into the HTL and photoactive layer which increased from 3.0 and 23.3% to 20.4 and 35.7% in photoactive layer and HTL, respectively. Similarly, the indium content reached to 17.9% on PEDOT:PSS surface and 0.4% on PCDTBT:PC₇₁BM surface in 1000 h. Core-level spectra of active layer indicate the oxidation of carbon atoms in the fullerene cage, oxidation of nitrogen present in the polymer matrix and formation of In₂O₃ due to indium diffusion. We also observed a steady fall in the optical absorption of the active layer during ageing in ambient air and it reduced to 76.5% of initial value in 1000 h. On the basis of these experimental results, we discussed key parameters that account for the degradation process and stability of OSCs in order to improve the device performance.     

用电子束工艺反转制造1:1精密掩模的工艺技术研究

本文主要描述了用电子束工艺反转技术制造1：1精密掩模的新方法，给出了从基本原理入手来确定工艺流程和选定工艺条件的过程，并给出制作实例说明了该项技术所取得的经济效益和社会效益。     

用后向SBS压缩电光调Q Cr:LiSAF激光脉冲宽度的研究

在抽运能量一定的条件下，采用强聚焦短焦距透镜提高焦点处的光功率密度，将Cr:LiSAF电光调Q激光器的输出脉冲聚焦于装有CS2介质的受激布里渊散射(SBS)池中，实现了宽线宽、多横模Cr:LiSAF激光脉冲的后向SBS，并观察到对激光脉宽的有效压缩。     

Improvements in the crystalline quality of PbxSn1−xTe crystals grown by vapor transport in a closed system

The quality of Pb_xSn_1−xTe crystals to be used in infrared detectors was improved by elimination or reduction in the number of holes, linear voids, strains and dislocations during growth. This was accomplished by use of stoichiometric or slightly Te-rich charges preheat treated before use to reduce the number of holes. Linear voids and strains were reduced by using constant diameter growth tubes of 25 mm diameter. The number of dislocations was reduced by the use of a slow cooling rate and limited contract with the walls of the growth tube.     

Comparison of spatial compositional uniformity and dislocation density for organometallic vapor phase epitaxial Hg1−x CdxTe grown by the direct alloy and interdiffused growth processes

Etch pit density and spatial compositional uniformity data are presented for organometallic vapor phase epitaxial Hg_1−x Cd_x Te grown by the direct alloy and interdiffused growth methods. For alloy growth, composition variation is as low as Δx=0.004 and 0.02 over 2- and 3-in diam areas, respectively; while for growth on CdZnTe substrates, etch pit density values lower than 2×10⁵ cm⁻² have been achieved. For interdiffused growth on CdZnTe, etch pit density values lower than 5×10⁵ cm⁻² have been obtained, while the composition variation is usually Δx≤0.004 and 0.014 over 2- and 3-in diam areas, respectively. Data demonstrate that the choice of particular CdZnTe substrate strongly affects the subsequent etch pit density measured in the layer. Reasonably uniform n-type doping over 3-in diam area using the source triethylgallium is also reported for both growth methods.     

Structure analysis of the system Hafnium/Silicon by means of X-ray photoelectron spectroscopy and X-ray photoelectron diffraction (XPD)

Due to the ongoing miniaturization of semiconductor devices new gate dielectrics are required for future applications. In this work we investigated hafnium silicide as a pre-system for hafnium oxide, one of the most promising candidates. One of the major problems of HfO₂-films on silicon is the formation of hafnium silicide at the HfO₂/Si interface. Therefore, ultrathin films of the system HfSi on with a systematic varied thickness from 3 to 30 Å were prepared. Measurements were conducted by means of X-ray photoelectron spectroscopy and low energy electron diffraction (LEED). Also full 2π X-ray photoelectron diffraction (XPD) patterns with high spectral resolution were recorded. Against other reports related to thicker films, several heating cycles showed no phase transitions of the ultrathin films. However, above temperatures of an island formation is strongly indicated. The experimental XPD patterns are compared to simulated patterns of model structures. For the first time we present a modification of the C49 structure a possible structure for ultrathin HfSi₂-films on bulk Si. As an outlook possibilities for preparing the system are introduced.     

The effect of Zn1‐xMgxO buffer layer deposition temperature on Cu(In,Ga)Se2 solar cells: A study of the buffer/absorber interface

The effect of atomic layer deposition temperature of Zn_1‐xMg_xO buffer layers for Cu(In,Ga)Se₂ (CIGS) based solar cell devices is evaluated. The Zn_1‐xMg_xO films are grown using diethyl zinc, bis‐cyclopentadienyl magnesium and water as precursors in a temperature range of 105 to 180°C. High efficiency devices are produced in the region from 105 up to 135°C. At a Zn_1‐xMg_xO deposition temperature of 120°C, a maximum cell efficiency of 15·5% is reached by using a Zn_1‐xMg_xO layer with an x‐value of 0·2 and a thickness of 140 nm. A significant drop in cell efficiency due to large losses in open circuit voltage and fill factor is observed for devices grown at temperatures above 150°C. No differences in chemical composition, structure and morphology of the samples are observed, except for the samples prepared at 105 and 120°C that show elemental selenium present at the buffer/absorber interface. The selenium at the interface does not lead to major degradation of the solar cell device efficiency. Instead, a decrease in Zn_1‐xMg_xO resistivity by more than one order of magnitude at growth temperatures above 150°C may explain the degradation in solar cell performance. From energy filtered transmission electron microscopy, the width of the CIGS/Zn_1‐xMg_xO chemical interface is found to be thinner than 10 nm without any areas of depletion for Cu, Se, Zn and O. Copyright © 2008 John Wiley & Sons, Ltd.     

Improvement of the cell performance in the ZnS/Cu(In,Ga)Se2 solar cells by the sputter deposition of a bilayer ZnO : Al film

ZnS is a candidate to replace CdS as the buffer layer in Cu(In,Ga)Se₂ (CIGS) solar cells for Cd‐free commercial product. However, the resistance of ZnS is too large, and the photoconductivity is too small. Therefore, the thickness of the ZnS should be as thin as possible. However, a CIGS solar cell with a very thin ZnS buffer layer is vulnerable to the sputtering power of the ZnO : Al window layer deposition because of plasma damage. To improve the efficiency of CIGS solar cells with a chemical‐bath‐deposited ZnS buffer layer, the effect of the plasma damage by the sputter deposition of the ZnO : Al window layer should be understood. We have found that the efficiency of a CIGS solar cell consistently decreases with an increase in the sputtering power for the ZnO : Al window layer deposition onto the ZnS buffer layer because of plasma damage. To protect the ZnS/CIGS interface, a bilayer ZnO : Al film was developed. It consists of a 50‐nm‐thick ZnO : Al plasma protection layer deposited at a sputtering power of 50 W and a 100‐nm‐thick ZnO : Al conducting layer deposited at a sputtering power of 200 W. The introduction of a 50‐nm‐thick ZnO : Al layer deposited at 50 W prevented plasma damage by sputtering, resulting in a high open‐circuit voltage, a large fill factor, and shunt resistance. The ZnS/CIGS solar cell with the bilayer ZnO : Al film yielded a cell efficiency of 14.68%. Therefore, the application of bilayer ZnO : Al film to the window layer is suitable for CIGS solar cells with a ZnS buffer layer. Copyright © 2012 John Wiley & Sons, Ltd.