Existence and atomic arrangement of microtwins in CdTe epilayers grown on GaAs (211) B substrates

Selected area electron diffraction pattern (SADP) and high-resolution transmission electron microscopy (HRTEM) measurements were carried out to investigate the existence and the atomic arrangement of microtwins in CdTe epilayers grown on GaAs (211) B substrates by using molecular beam epitaxy. The SADP results showed that an epitaxial relationship between the CdTe epilayer and the GaAs substrate was formed. The lattice of the CdTe (211) tilts about 2° with respect to the GaAs (211) B substrate about the CdTe [110]∥GaAs [110] common zone axis. The HRTEM images showed that microtwins were formed in the CdTe epilayers. A possible atomic arrangement of the microtwins is presented on the basis of the HRTEM result. The present observations can help to improve understanding of the microstructural properties in CdTe epilayers grown on GaAs substrates.     

Dependence of the microstructural properties on the substrate temperature in strained CdTe (1 0 0)/GaAs (1 0 0) heterostructures

CdTe thin films were grown on GaAs (1 0 0) substrates by using molecular beam epitaxy at various temperatures. The bright-field transmission electron microscopy (TEM) images and the high-resolution TEM (HRTEM) images showed that the crystallinity of CdTe epilayers grown on GaAs substrates was improved by increasing the substrate temperature. The result of selected-area electron diffraction pattern (SADP) showed that the orientation of the grown CdTe thin films was the (1 0 0) orientation. The lattice constant the strain, and the stress of the CdTe thin film grown on the GaAs substrate were determined from the SADP result. Based on the SADP and HRTEM results, a possible atomic arrangement for the CdTe/GaAs heterostructure is presented.     

分子束外延生长Sb薄膜及其量子尺寸效应

在GaAs(001)衬底上，用分子束外延生长Sb(111)薄膜，用反射式高能电子衍射仪原位监控生长过程，用透射电子显微镜观察薄膜结构，并用van der Pauw方法测量了电阻率随生长温度的变化，观察到Sb薄膜半金属/半导体转变及其量子尺寸效应． 关键词：     

Electron microscopy investigation of GaAs(100)-(Ga2Se3)-GaAs nanostructures

The GaAs(100)-Ga₂Se₃ heterostructures have been investigated by transmission and scanning electron microscopy. The sequence of structural transformations at the GaAs(100) surface during treatment in selenium vapor has been determined. It has been found that the preliminary treatment of the GaAs(100) surface in selenium vapor increases the orienting effect of the GaAs(100) substrate on the GaAs film growth.     

Nanoscale spatial phase modulation of GaAs growth in V-grooved trenches on Si(001) substrate

This letter reports the nanoscale spatial phase modulation of Ga As growth in V-grooved trenches fabricated on a Si(001) substrate by metal–organic vapor-phase epitaxy. Two hexagonal Ga As regions with high density of stacking faults parallel to Si {111} surfaces are observed. A strain-relieved and defect-free cubic phase Ga As was achieved above these highly defective regions. High-resolution transmission electron microscopy and fast Fourier transforms analysis were performed to characterize these regions of Ga As/Si interface. We also discussed the strain relaxation mechanism and phase structure modulation of Ga As selectively grown on this artificially manipulated surface.     

关于RHEED振荡技术优化GaAs(110)量子阱生长的研究

在GaAs(110)衬底上生长的半导体材料有诸多优良性能，使得在非极性GaAs(110)衬底上获得高质量各类异质结材料，成为近年来分子束外延生长关注的课题.考虑GaAs(110)表面是Ga和As共面，最佳生长温度窗口很小；反射式高能电子衍射的(1×1)再构图案对生长温度和V/Ⅲ束流比不敏感，难于通过观察再构图案的变化，准确地找到最佳生长条件.作者在制备GaAs(110)量子阱过程中，观察到反射式高能电子衍射强度振荡呈现出的单双周期变化.这意味着不同工艺条件下，在 GaAs(110)衬底上量子阱有单层和双层两种生长模式.透射电子显微镜和室温光致荧光光谱测量结果表明：在双层生长模式下量子阱样品光学性能较差，而在单层生长模式下量子阱光学性能较好，但是界面会变粗糙.利用这一特点，我们采用反射式高能电子衍射强度振荡技术，找到了一种在GaAs(110)衬底上生长高质量量子阱的可行方法. 关键词： 反射高能电子衍射 量子阱 分子束外延     

GaAs(001)表面外延生长Mn薄膜的XPS研究

利用x射线光电子能谱的深度剖面技术,对不同衬底温度下分子束外延生长的Mn薄膜及其与GaAs(001)衬底间的界面进行了元素组分和化学结合状态随深度变化的研究。实验发现衬底温度等于400K时制备的fcc-Mn/GaAs(001)体系中,fcc-Mn层与GaAs衬底之间存在一层较厚的Mn-Ga-As的缓冲层;衬底温度等于300K(室温)时制备的a-Mn/GaAs(001)体系中也存在类似的缓冲层,但它的厚度与fcc-Mn的情形相比要小得多;而当衬底温度等于450K时制备的体系在GaAs衬底之上全部是Mn-Ga     

The surface plasmon resonance of metal-film nanohole arrays

In this paper we investigated the enhanced transmission and surface plasmon resonance through a thin gold film with a periodic array of subwavelength nanoholes. Both freestanding gold-film nanohole arrays and gold-film nanohole arrays deposited on a gallium arsenide (GaAs) substrate are considered. Periodic arrays of nanoholes exhibit two different surface plasmon resonance features: localized waveguide resonance and the well-recognized photonic crystal resonance. The tangential electric field component $Ey$ is nonzero only in the hole region for a freestanding gold-film nanohole array, but it can exist in the hole region and in the metallic region for a gold-film nanohole array deposited on a GaAs substrate.     

Unusual role of the substrate in droplet‐induced GaAs/AlGaAs quantum‐dot pairs

The structural complexity of GaAs quantum‐dot pairs has been revealed by cross‐sectional transmission electron microscopy. As a result of high‐temperature droplet epitaxy, the AlGaAs substrate beneath the quantum‐dot pairs is no longer immobile and its reconstruction is observed to define the crystallization of gallium droplets under an arsenic flux. The GaAs quantum‐dot pairs are immersed into the substrate and further confined by the re‐distributed AlGaAs materials above the substrate plane. There are two underlying mechanisms responsible for the final nanostructure configuration, melt‐back etching by the gallium droplets and preferential crystallization of gallium around reconstructed sidewalls. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Growth and characterization of oriented CdSe nanobelts and nanorods

Oriented CdSe nanobelts and nanorods were grown successfully on GaAs and Si substrates by metal organic chemical vapor deposition. The thickness of Au film coated on the substrate plays an important role in determining the orientation, size, and density of these one-dimensional CdSe nanostructures. Preferred orientation was observed for nanostructures grown on the GaAs substrate coated with thick Au film, but not for the nanostructures grown on the Si substrate. Photoluminescence, transmission electron microscope, and X-ray diffraction measurements show that the CdSe nanostructures could have either wurtzite or zinc-blende structures, and there are more nanostructures with wurtzite structure than with zinc-blende structure.     

Optical and structural characterization of a self-aligned single electron transitor structure by cathodoluminescence microscopy

We report about optical and structural investigations of a self-aligned single electron transistor (SET) structure using cathodoluminescence-(CL) and transmission electron microscopy (TEM). The SET structures were fabricated by MBE growth of GaAs/AlAs on different prepatterned GaAs (1 0 0) substrates. This technique for the in situ formation of nanoscopic semiconductor heterostructures is presently a widely used and promising approach for the fabrication of low-dimensional systems like quantum wires and quantum dots (QD). The active region of the SET structure consists of a GaAs/AlGaAs-QD formed by thickness modulation of a single quantum well (SQW) during the MBE growth. The position and the size of the QD is defined by the design of the substrate pattern. The thickness modulation of the GaAs-SQW is evidenced by TEM investigations. The lateral confinement potential given by the thickness modulation of GaAs-SQW is directly imaged by CL microscopy.     

空间用GaInP/GaAs/In0.3Ga0.7 As(1 eV)倒装三结太阳电池研制

采用阶变缓冲层技术 (step-graded) 外延生长了具有更优带隙组合的倒装GaInP/GaAs/In_0.3Ga_0.7As(1.0 eV) 三结太阳电池材料, TEM和HRXRD测试表明晶格失配度为2%的In_0.3Ga_0.7As 底电池具有较低的穿透位错密度和较高的晶体质量, 达到太阳电池的制备要求. 通过键合、剥离等工艺制备了太阳电池芯片. 面积为 10.922 cm² 的太阳电池芯片在空间光谱条件下转换效率达到32.64% (AM0, 25 ℃), 比传统晶格匹配的 GaInP/GaAs/Ge(0.67 eV) 三结太阳电池的转换效率提高3个百分点. 关键词： 太阳电池 三结 倒装结构     

Strain relaxation in epitaxial GaAs/Si (0 0 1) nanostructures

Abstract

Crystal defects, present in ~100 nm GaAs nanocrystals grown by metal organic vapour phase epitaxy on top of (0 0 1)-oriented Si nanotips (with a tip opening 50–90 nm), have been studied by means of high-resolution aberration-corrected high-angle annular dark-field scanning transmission electron microscopy. The role of 60° perfect, 30° and 90° Shockley partial misfit dislocations (MDs) in the plastic strain relaxation of GaAs on Si is discussed. Formation conditions of stair-rod dislocations and coherent twin boundaries in the GaAs nanocrystals are explained. Also, although stacking faults are commonly observed, we show here that synthesis of GaAs nanocrystals with a minimum number of these defects is possible. On the other hand, from the number of MDs, we have to conclude that the GaAs nanoparticles are fully relaxed plastically, such that for the present tip sizes no substrate compliance can be observed.     

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.     

Generation and propagation of a picosecond acoustic pulse at a buried interface: time-resolved x-ray diffraction measurements

We report on the propagation of coherent acoustic wave packets in (001) surface oriented Al0.3Ga0.7As/GaAs heterostructure, generated through localized femtosecond photoexcitation of the GaAs. Transient structural changes in both the substrate and film are measured with picosecond time-resolved x-ray diffraction. The data indicate an elastic response consisting of unipolar compression pulses of a few hundred picosecond duration traveling along [001] and [001] directions that are produced by predominately impulsive stress. The transmission and reflection of the strain pulses are in agreement with an acoustic mismatch model of the heterostructure and free-space interfaces.     

Al/GaAs界面反应的XPS研究

用XPS研究了清洁无序GaAs表面沉积超薄Al膜后的界面反应,结果表明,原沉积于GaAs表面的Al能进入GaAs衬底取代Ga形成AlAs,而通过Al-Ga替位反应释放出来的Ga则残留在衬底表面,提出了Ga/AlAs+GaAs/GaAs三层结构模型。 关键词：     

Stranski–Krastanow growth of multilayer In(Ga)As/GaAs QDs on Germanium substrate

We have described Stranski–Krastanow growth of multilayer In(Ga)As/GaAs QDs on Ge substrate by MBE. The growth technique includes deposition of a thin germanium buffer layer followed by migration-enhanced epitaxy (MEE) grown GaAs layer at 350°C. The MEE layer was overgrown by a thin low-temperature (475°C) grown GaAs layer with a subsequent deposition of a thick GaAs layer grown at 590°C. The sample was characterized by AFM, cross-sectional TEM and temperature-dependent PL measurements. The AFM shows dense formation of QDs with no undulation in the wetting layer. The XTEM image confirms that the sample is free from structural defects. The 8 K PL emission exhibits a 1051 nm peak, which is similar to the control sample consisting of In(Ga)As/GaAs QDs grown on GaAs substrate, but the observed emission intensity is lower. The similar slopes of Arrhenius plot of the integrated PL intensity for the as-grown QD sample grown on Ge substrate as well as for a reference QD sample grown on GaAs substrate are found to be identical, indicating a similar carrier emission process for both the samples. This in turn indicates coherent formation of QDs on Ge substrate. We presume due to the accumulated strain associated with the self-assembled growth of nanostructures on Ge that nonradiative recombination centers are introduced in the GaAs barrier in between the QD layers, which in turn degrades the overall optical quality of the sample.     

An investigation of misfit dislocations in Al on (001) GaAs grown by chemical beam epitaxy

We report a transmission electron microscope study of the morphology and interfacial structure of Aluminium grown on (001) GaAs by chemical beam epitaxy (CBE). The Al grows in islands for all thicknesses deposited, and exhibits four distinct orientation relationships with respect to the substrate. One of these orientation relationships becomes dominant as growth progresses, with (011)_Al parallel to (001)_GaAs. Misfit dislocations can be seen in the interface between this orientation and the substrate with Burgers vector 1/4(110)_GaAs, and a crystallographic analysis shows that these dislocations are associated with interfacial steps of height 1/2[001]_GaAs. In (001)Al on (001)GaAs, the existence of these dislocations has in the past been regarded as evidence for the existence of a rigid-body shift of the Al in the interfacial plane. Using cross-sectional high-resolution TEM, it is shown that this shift is not present in the (011) orientation. The similarity in the microstructure and crystallography of the (001) and (011) orientations leads us to suggest that there is also no shift in (001) Al on (001)GaAs. This is in conflict with previous investigations of this system using a wide variety of techniques.     

GaAs/AlAs super-flat interfaces in GaAs/AlAs and GaAs/(GaAs) (AlAs) quantum wells grown on (4 1 1)A GaAs substrates by MBE

Effectively atomically flat GaAs/AlAs interfaces over a macroscopic area (“super-flat interfaces”) have been realized in GaAs/AlAs and GaAs/(GaAs) (AlAs) quantum wells (QWs) grown on (4 1 1)A GaAs substrates by molecular beam epitaxy (MBE). A single and very sharp photoluminescence (PL) peak was observed at 4.2 K from each GaAs/AlAs or GaAs/(GaAs) (AlAs) QW grown on (4 1 1)A GaAs substrate. The full-width at half-maximum (FWHM) of a PL peak for GaAs/AlAs QW with a well width ( ) of 4.2 nm was 4.7 meV and that for GaAs/(GaAs) (AlAs) QW with a smaller well width of 2.8 nm (3.9 nm) was 7.6 meV (4.6 meV), which are as narrow as that for an individual splitted peak for conventional GaAs/AlAs QWs grown on (1 0 0) GaAs substrates with growth interruption. Furthermore, only one sharp peak was observed for each GaAs/(GaAs) (AlAs) QW on the (4 1 1)A GaAs substrate over the whole area of the wafer (7 7 mm ), in contrast with two- or three-splitted peaks reported for each GaAs/AlAs QW grown on the (1 0 0) GaAs substrate with growth interruption. These results indicate that GaAs/AlAs super-flat interfaces have been realized in GaAs/AlAs and GaAs/(GaAs) (AlAs) QWs grown on the (4 1 1)A GaAs substrates.