GaAs/Ge/GaAs Heterostructures for Use in Nonlinear Optics

GaAs/Ge/GaAs heterostructures with sublattice reversed GaAs on Ge epilayers grown via molecular beam epitaxy (MBE) for periodic domain inverted structures are presented. For the first time, such structures are grown in separate MBE machines for GaAs and Ge with atmospheric wafer transfer. The high quality of the heterostructures is confirmed via X-ray diffraction and photoluminescence. It is proposed that the surfactants (Bi, Sb) be used to control the nucleation of GaAs epilayers on a Ge epilayer.     

Homoepitaxial superlattices with nonoriented barrier layers

Stimulation possibilities of epitaxial film growth on amorphous and polycrystal layers covering the surface of the orienting substrate are shown. Multilayer periodical structures of superthin (L < 100 Å) single-crystal InSb or PbTe films alternating with nonoriented GaAs, C or Ge layers have been obtained and investigated.     

Far infrared absorption of amorphous GaAs and Ge

Far infrared reflection spectra of amorphous GaAs and Ge have been obtained in the frequency region from 30–600 cm^?1. For each material, curves of ω?₂ vs frequency have been obtained whose corresponding reflectivity curves give a best fit to the data. The peak value of the abdorption coefficient is about 4000 cm^?1 for GaAs and 160 cm^?1 for Ge. The results are compared with Raman spectra and with theoretical calculations.     

Growth and properties of GaAs and GaN films and low-dimensional GaAs/QWsInGaAs structures on Si substrates with a Ge buffer layer

The conditions for producing mirror-smooth Ge buffer layers of uniform size on Si(100) and Si(111) substrates by means of hot wire chemical vapor deposition (HW-CVD) at a low temperature (350°C) are determined. Single-crystal GaN and GaAs films and low-dimensional GaAs/QWInGaAs/ GaAs/QWInGaAs/GaAs/Ge/Si structures of uniform smoothness are obtained via MOVPE at reduced pressures. Their quantum wells are found to be characterized by intense photoluminescence comparable in intensity to that produced on GaAs substrates.     

GaAs(111)表面硅烯、锗烯的几何及电子性质研究

基于密度泛函理论的第一性原理计算方法, 系统研究了硅烯、锗烯在GaAs(111) 表面的几何及电子结构. 研究发现, 硅烯、锗烯均可在As-中断和Ga-中断的GaAs(111) 表面稳定存在, 并呈现蜂窝状六角几何构型. 形成能计算结果证明了其实验制备的可行性. 同时发现硅烯、锗烯与GaAs表面存在共价键作用, 这破坏了其Dirac电子性质. 进一步探索了利用氢插层恢复硅烯、锗烯Dirac电子性质的方法. 发现该方法可使As-中断面上硅烯、锗烯的Dirac电子性质得到很好恢复, 而在Ga-中断面上的效果不够理想. 此外, 基于原子轨道成键和杂化理论揭示了GaAs表面硅烯、锗烯能带变化的物理机理. 研究结果为硅烯、锗烯在半导体基底上的制备及应用奠定了理论基础.     

Surface structure of GaAs(211)

The atomic structures of the two inequivalent (211) surfaces of GaAs have been investigated by LEED. Both surfaces, prepared by etching and heat-cleaning or ion-sputtering and annealing, are unstable and develop large (110) facets which exhibit the atomic geometry of the (110) GaAs surface. These facets entirely cover the surface. Three sets of facets, making 30°, 30° and 54° angles with the (211) plane, are detected on one surface. Only two sets, making 30° angles with the (211) plane, are detected on the other. The reasons for this difference are not understood at this time. The LEED study of Si(211) and Ge(211) shows that the Si surface is flat whereas the Ge surface exhibits reconstructed (311) facets. The structural difference between the (211) surfaces of GaAs and Ge and the facetting of the compound are invoked to explain the problems encountered in the MBE growth of GaAs on Ge(211).     

Valence band state densities of tetrahedrally coordinated amorphous semiconductors

A novel technique, for obtaining the valence band state densities (VBSD's) of tetrahedrally coordinated amorphous semiconductors from normal incidence reflectance data, is applied to Si and Ge and GaP, GaAs and GaSb. The VBSD's of Si and Ge are similar to other published results, obtained by conventional techniques, and cannot be described by broadened crystalline VBSD's. On the other hand, the VBSD's of the 3–5's contain many of the crystalline features. The relation of these results to the structure of the amorphous phase is discussed.     

Molecular beam epitaxy growth of GaAs on an offcut Ge substrate

Molecular beam epitaxy growth of GaAs on an offcut Ge (100) substrate has been systemically investigated. A high quality GaAs/Ge interface and GaAs film on Ge have been achieved. High temperature annealing before GaAs deposition is found to be indispensable to avoid anti-phase domains. The quality of the GaAs film is found to strongly depend on the GaAs/Ge interface and the beginning of GaAs deposition. The reason why both high temperature annealing and GaAs growth temperature can affect epitaxial GaAs film quality is discussed. High quality In_0.17Ga_0.83As/GaAs strained quantum wells have also been achieved on a Ge substrate. Samples show flat surface morphology and narrow photoluminescence line width compared with the same structure sample grown on a GaAs substrate. These results indicate a large application potential for III--V compound semiconductor optoelectronic devices on Ge substrates.     

Bandstruwre dependence of impact ionisation in semiconductors from high pressure studies

Abstract

Hydrostatic pressure has been used to study the bandstructure dependence of impact ionisation in Si, GaAs and Ge photodiodes. The results were modeled using lucky drift and Monte Carlo calculations, with ionisation threshold energies calculated from model pseudopotential bandstructures. The results for Si, GaAs and Ge were significantly different, and were interpreted in terms of the different band structures. For Si, multiplication is dominated by electron ionisation in the A valleys due to the large intervalley separations. However for GaAs and Ge ionisation gives rise to final electron states which are not only in the lowest conduction-band valley as previously assumed, but throughout the Brillouin zone. This has important implications for our understanding of impact ionisation and for modelling of avalanche multiplication in semiconductor alloys and multilayers.     

镶嵌型纳米锗的制备新方法及其光致发光研究

报道了通过热氧化氢化非晶锗硅薄膜和氢化非晶硅／氢化非晶锗多层膜以制备镶嵌于二氧化硅中纳米锗材料的新方法。研究结果表明：在经过氧化处理后,薄腊在的Ｓｉ与Ｏ结合形成氧化硅同时单晶Ｇｅ被析出形成了镶嵌型的纳米Ｇｅ颗粒;在Ａｒ＾＋激光（４８８ｎｍ）的激发下,观察到了室温下的光致民光现象。发光峰中心位于２．２ｅＶ。由多层腊制备出的样吕其发光强度相对加强,且半高宽也显著变窄,表明利用多层膜可较好地控制尺寸分布     

Orientation-patterned templates GaAs/Ge/GaAs for nonlinear optical devices. I. Molecular beam epitaxy

GaAs/Ge/GaAs heterostructures in which the GaAs layer lattice on Ge is rotated at a right angle to the substrate plane are grown by molecular-beam epitaxy (MBE). Such heterostructures are grown in different epitaxial setups for GaAs and for Ge with wafer transfer through air tor the first time. It is proposed to use surfactants (Bi, Sb) to control GaAs layer nucleation on Ge.     

FDTD法对二维正方格子光子晶体带隙的数值计算

通过optiFDTD模拟软件对二维椭圆柱构造的正方格子光子晶体的禁带特性进行了数值模拟。分别研究了在空气中椭圆介质(Ge,Si,GaAs)柱和在介质(Ge,Si,GaAs)中椭圆空气柱构造的二维正方格子光子晶体中椭圆柱的横轴半径和纵轴半径的大小,以及椭圆柱的不同旋转角度对光子禁带的影响;并计算出了在上述两种情况下的空气和介质中的最优结构参数。     

GaInP/GaAs/Ge三结太阳电池不同能量质子辐照损伤模拟

以GaInP/GaAs/Ge三结太阳电池为研究对象,开展了能量为0.7, 1, 3, 5, 10 MeV的质子辐照损伤模拟研究,建立了三结太阳电池结构模型和不同能量质子辐照模型,获得了不同质子辐照条件下的I-V曲线,光谱响应曲线,结合已有实验结果验证了本文模拟结果,分析了三结太阳电池短路电流、开路电压、最大功率、光谱响应随质子能量的变化规律,利用不同辐照条件下三结太阳电池最大输出功率退化结果,拟合得到了三结太阳电池最大输出功率随位移损伤剂量的退化曲线.研究结果表明,质子辐照会在三结太阳电池中引入位移损伤缺陷,使得少数载流子扩散长度退化幅度随质子能量的减小而增大,从而导致三结太阳电池相关电学参数的退化随质子能量的减小而增大.相同辐照条件下,中电池光谱响应退化幅度远大于顶电池光谱响应退化幅度,中电池抗辐照性能较差,同时中电池长波范围内光谱响应的退化幅度比短波范围更大,表明中电池相关电学参数的退化主要来源于基区损伤.     

GaAs/Ge的MOCVD生长研究

用常压MOCVD在Ge衬底上外延生长了GaAs单晶层,研究了GaAs和6e的极性与非极性材料异质外延生长,获得了质量优良的GaAs/Ge外延片,GaAs外延层X射线双晶衍射回摆曲线半高宽达16弧秒.10K下PL谱半峰宽为7meV.讨论了极性与非极性外延的界面反相畴问题和GaAs-Ge界面的Ga、Ge原子互扩散问题.     

Electrophysical properties of gallium arsenide in combination with impurity-doped germanium and isovalent indium and antimony impurities

The temperature dependence of the charge carrier concentration and mobility in n-type GaAs monocrystals doped jointly by Ge and isovalent In and Sb impurities is investigated. The observable charge carrier concentration and mobility changes in the GaAs:Ge:In and GaAs:Ge:Sb are compared with the corresponding characteristics in GaAs:Ge, and the change in properties along the ingots can be explained by the Ge impurity redistribution in the gallium and arsenic sublattices in the presence of an isovalent impurity.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 3–8, September, 1987.     

Nonexistence of localized band tail states in substitutional semiconductor alloys and some other disordered systems

A recent theory of semiconducting glasses seems to imply a substantial density of localized band tail states in substitutional semiconductor alloys, such as Sie or GaAsP, and also in homogenous strain-free amorphous Si and Ge. Experimental evidence against the existence of such states in these non-glassy disordered materials is overwhelming. The paradox is resolved by noting that if the material is in thermodynamic equilibrium, the disorder of the atomic potentials will not result in disorder of the valence or conduction band energy levels.     

Ab Initio computer simulation of the early stages of crystallization: application to Ge(2)Sb(2)Te(5) phase-change materials

By virtue of the ultrashort phase-transition time of phase-change memory materials, e.g., Ge(2)Sb(2)Te(5), we successfully reproduce the early stages of crystallization in such a material using ab initio molecular-dynamics simulations. A stochastic distribution in the crystallization onset time is found, as generally assumed in classical nucleation theory. The critical crystal nucleus is estimated to comprise 5-10 (Ge,Sb)(4)Te(4) cubes. Simulated growth rates of crystalline clusters in amorphous Ge(2)Sb(2)Te(5) are consistent with extrapolated experimental measurements. The formation of ordered planar structures in the amorphous phase plays a critical role in lowering the interfacial energy between crystalline clusters and the amorphous phase, which explains why Ge-Sb-Te materials exhibit ultrafast crystallization.     

高温处理工艺对低压MOCVD外延GaAs/Ge太阳电池的影响

采用自制的低压金属有机化学汽相淀积LP-MOCVD设备,在Ge衬底(100)面向(111)偏9°外延生长出GaAs电池结构,对电池材料进行了X射线衍射分析另外,对由此材料制成的太阳电池进行了性能测试,测试结果表明,Ge衬底的高温处理工艺对GaAs/Ge太阳电池的电流电压特性有一定的影响试验表明,在600～700℃之间高温处理效果较好。     

Electrical and ellipsometry study of sputtered SiO2 structures with embedded Ge nanocrystals

SiO₂ layer structures with a middle layer containing Ge nanocrystals were prepared by sputtering on n- and p-type Si substrates, and by consecutive annealing. Ge content in the middle layer was varied in the range of 40-100%. Most of the structures exhibited low breakdown voltages. The current through the structures became Schottky-like after breakdown. However, some p-type samples showed a considerable memory effect. It was obtained by spectroscopic ellipsometry that the middle layer contains amorphous Ge phase as well. The results also suggest intermixing of the layers during the sputtering and/or the annealing process.     

Crystallization of isolated amorphous zones in semiconductors

Thermal annealing, irradiation with electrons (25-300 keV), and irradiation with photons (hν = 2.33-3.88 eV) have been used to stimulate the crystallization of isolated amorphous zones in Si, Ge, GaAs, GaP and InP. Transmission electron microscopy and computer image analysis were used to determine the crystallization processes. For all materials, thermally stimulated crystallization occurred only at temperatures above 373 K. The electron-stimulated crystallization rate is sensitive to the electron energy. Initially, the rate decreases with increasing energy until it reaches a minimum at about one half the threshold displacement energy and then it increases. It is insensitive to the irradiation temperature between 90 and 300 K and to the crystal orientation. The effective diameter of the amorphous zone initially shrinks linearly with increasing electron dose. For the laser-induced crystallization experiments the crystallization rate in Si, but not in Ge, was sensitive to the temperature, with a faster rate occurring at 300 K than at 90 K. The photon and electron stimulated crystallization results indicate that a non-displacive mechanism causes bond breakage at the amorphous-crystalline interface. The re-formation of these interfacial bonds is responsible for the amorphous-to-crystalline transition.