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. (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.)     

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.     

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     

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.     

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。     

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.     

Realization of in-situ sub two-dimensional quantum structures by strained layer growth phenomena in the InxGa1- xAs/GaAs system

We confirm that as the misfit strain in pseudomorphic epitaxial layer increases, surface thermodynamics controlled growth modes can change from a layer-by-layer to a three-dimensional (3-D) island mode. Both in-situ reflection high energy electron diffraction studies and in-situ scanning tunneling microscopy studies are utilized to demonstrate this transition to 3-D growth. This concept allows one to grow GaAs/In_xGa_1-xAs/GaAs heterostructures where the electrons in In_xGa_1-xAs are possibly confined in lower dimensions.     

Structural characterization of GaAs<Subscript>1−x</Subscript>Bi<Subscript>x</Subscript> alloy by rutherford backscattering spectrometry combined with the channeling technique

Rutherford backscattering spectrometry (RBS) combined with the channeling technique has been applied to a GaAs_1−xBi_x epilayer to investigate concentration and lattice location of Bi atoms and crystalline quality of the epilayer. The metastable GaAs_1−xBi_x alloy layer was grown on a GaAs substrate at a temperature as low as 365°C. The GaBi mole fraction obtained was 2.6 ± 0.2%. Angular scans for [100] and [111] crystal directions reveal that the incorporated Bi atoms exactly occupy substitutional sites in the GaAs crystal lattice. Crystal perfection of the GaAs_1−xBi_x metastable alloy is fairly good in spite of the low growth temperature.     

Optical and electrical properties of epitaxial (Mg,Cd)xZn1−xO, ZnO, and ZnO:(Ga,Al) thin films on c-plane sapphire grown by pulsed laser deposition

A consistent set of epitaxial, n-type conducting ZnO thin films, nominally undoped, doped with Ga or Al, or alloyed with Mg or Cd, was grown by pulsed laser deposition (PLD) on single-crystalline c-plane sapphire (0 0 0 1) substrates, and characterized by Hall measurement, and UV/VIS optical transmission spectroscopy.The optical band gap of undoped ZnO films at nearly 3.28 eV was shifted by alloying with Mg up to 4.5 eV and by alloying with Cd down to 3.18 eV, dependent on the alloy composition. In addition, highly doped ZnO:Al films show a blue-shifted optical absorption edge due to filling of electronic states in the conduction band.The Hall transport data of the PLD (Mg,Zn,Cd)O:(Ga,Al) thin films span a carrier concentration range of six orders of magnitude from 3 × 10¹⁴ to 3 × 10²⁰ cm⁻³, which corresponds to a resistivity from 5 × 10⁻⁴ to 3 × 10³ Ω cm. Structurally optimized, nominally undoped ZnO films grown with ZnO nucleation and top layer reached an electron mobility of 155 cm²/V s (300 K), which is among the largest values reported for heteroepitaxial ZnO thin films so far.Finally, we succeeded in combining the low resistivity of ZnO:Ga and the band gap shift of MgZnO in MgZnO:Ga thin films. This results demonstrate the unique tunability of the optical and electrical properties of the ZnO-based wide-band gap material for future electronic devices.