Suppression of twin formation in CdTe(111)B epilayers grown by molecular beam epitaxy on misoriented Si(001)

CdTe(lll)B layers have been grown on misoriented Si(001). Twin formation inside CdTe(lll)B layer is very sensitive to the substrate tilt direction. When Si(001) is tilted toward [110] or [100], a fully twinned layer is obtained. When Si(001) is tilted toward a direction significantly away from [110], a twin-free layer is obtained. Microtwins inside the CdTe(111)B layers are overwhelmingly dominated by the lamellar twins. CdTe(111)B layers always start with heavily lamellar twinning. For twin-free layers, the lamellar twins are gradually suppressed and give way to twin-free CdTe(111)B layer. The major driving forces for suppressing the lamellar twinning are the preferential orientation of CdTe[11-2] along Si[1-10] and lattice relaxation. Such preferential orientation is found to exist for the CdTe(111)B layers grown on Si(001) tilted toward a direction between [110] and [100].     

Optical anisotropy and photoluminescence temperature dependence for self-assembled InAs quantum islands grown on vicinal (001) InP substrates

In this paper, we report on a detailed investigation of the effect of misorientated InP(001) substrates on the optical properties of InAs quantum islands grown by molecular beam epitaxy in the Stranski-Krastanow regime. Temperature-dependent photoluminescence and polarization of photoluminescence (PPL) are studied. PPL shows a high degree of linear polarization, near 40%, for the sample grown on the substrate with 2° off miscut angle towards [110] direction (2°F) and only 16% for the sample grown on the substrate with 2° off miscut angle towards [010] direction (2°B). This result pointing out the growth of InAs quantum wires (QWr) on 2°F substrate and of quasi-isotropic InAs quantum dots (QD) on 2°B substrate. The luminescence remains strong at 300 K as much as 36% of that at 8 K, indicating a strong spatial localization of the carriers in the InAs QIs grown on InP(001).     

GaAs(001)基底取向误差对GaAs/Al_(0.3)Ga_(0.7)As中局域声子的影响(英文)

We have studied the confined phonons in GaAs/Al0 3Ga0.7As superlat-tice grown by molecular beam epitaxy on oriented and misoriented GaAs (001) substrates. Raman scattering measurements have been performed at room- and low-temperatures. The results show that the phonon features in the superlattice-grown on GaAs(001) misoriented 4° toward the [110] direction are significantly different from those in the precisely oriented sample. The difference is discussed in terms of misorientation induced atomic-steps at GaAs-Al0.3Ga0.7As interfaces.     

Photoluminescence of InAs quantum dots grown on disoriented GaAs substrates

The photoluminescence spectra in an external magnetic field of an ensemble of InAs quantum dots grown by molecular beam epitaxy on a (001) GaAs substrate with a disorientation in the [010] direction are studied. A redistribution of the photoexcited carriers among different groups of dots under the influence of the magnetic field is observed. The concentration of quantum dots is determined by analyzing the data. Fiz. Tekh. Poluprovodn. 33, 1084–1087 (September 1999)     

Local lattice parameter determination of a silicon (001) layer grown on a sapphire (1102) substrate using convergent-beam electron diffraction

All the six lattice parameters (a, b, c, alpha, beta and gamma) of a Si (001) layer grown on a sapphire (1102) substrate were determined by convergent-beam electron diffraction with no assumption of crystal lattice symmetry. A lattice compression in the Si (001) plane and an elongation in the [001] direction were revealed. An anisotropic lattice compression in the (001) plane was clearly detected for the first time. That is, the lattice compression in the Si [100] direction, which is parallel to the sapphire [1101] direction, was larger than that of the Si [010] direction, which is parallel to the sapphire [1120] direction. It was also revealed that the lattice parameters of the Si-layer depend on the distance from the interface. Anisotropy of carrier mobility was reasonably explained in terms of the anisotropy of the lattice parameters determined.     

Growth of InAs quantum dots on vicinal GaAs(001) surfaces misoriented in the [010] direction

Atomic-force microscopy (AFM) is used to study InAs quantum-dot structures grown by molecular-beam epitaxy (MBE) on vicinal GaAs(001) surfaces misoriented in the [010] direction by 1, 2, 4, and 6°. It is shown for a chosen misorientation direction that a vicinal GaAs(010) surface is covered with a network of stepped terraces. The thickening of the network of terraces with increasing misorientation angle leads to the suppression of adatom surface diffusion and makes it possible to achieve higher densities and more uniform ensembles of quantum dots, while simultaneously decreasing the probability of their coalescence. Fiz. Tekh. Poluprovodn. 32, 860–865 (July 1998)     

Molecular beam epitaxy—Grown ZnSe nanowires

Molecular beam epitaxy (MBE) via the vapor-liquid-solid (VLS) reaction was used to grow ZnSe nanowires (NWs) on (111), (100), and (110) oriented GaAs substrates. Through detailed transmission electron microscopy (TEM) studies, it was found that 〈111〉 orientation is the growth direction for NWs with size ≥30 nm, while NWs with size around 10 nm prefer to grow along the 〈110〉 direction, with a small portion along the 〈112〉 direction. These observations have led to the realization of vertical ZnSe NWs with size around 10 nm grown on a GaAs (110) substrate. An ordered ZnSe NW array fabricated on a GaAs (111) substrate with a novel prepatterning method associated with plasma etching shows a high degree of ordering and a good size uniformity of the as-grown NWs. The diameter of the NWs in the array is around 80 nm and most of them are found to orient vertically, but some tilt to one of the six possible directions of the 〈111〉 family.     

N-型ZnSe:Cl的分子束外延生长

本文报道利用分子束外延(MBE)技术,采用高纯ZnCl_2作掺杂源,成功地进行了n—型ZnSe:Cl的分子束外延生长。n-ZnSe:Cl/p-GaAs异质结构的伏-安(I—V)特性和热探针测试显示外延层呈n型导电特性。反射高能电子衍射(RHEED)和x射线衍散谱测量表明ZnSe:Cl外延层具有较好的晶体质量。     

Growth of high quality CdTe on Si substrates by molecular beam epitaxy

We have systematically studied the growth of CdTe (lll)B on Si(001)with different atomic step structures, defined uniquely by miscut tilt angle and direction. X-ray double crystal rocking curve (DCRC) analysis has been used to evaluate the crystalline quality and twin content of the films. High-resolution electron microscopy has been used to examine the CdTe(lll)B/Si(001) interface and to follow the microstructural evolution as a function of distance from the interface. Our results show that the formation of double domains and twins is very sensitive to the tilt parameters. When growth conditions are optimized, twins are not observed at distances greater than about 2.5 microns from the substrate surface. The best quality films exhibit a DCRC FWHM of 60 arc sec, for a film thickness of 17 μm, the lowest value ever reported for heteroepitaxial growth of CdTe on Si or GaAs. In efforts to improve the nucleation process, precursors such as Te and As have been used, and we have shown that they improve the stability of the heterointerface.     

Epitaxial Growth of Large‐Scale Orthorhombic CsPbBr3 Perovskite Thin Films with Anisotropic Photoresponse Property

Inorganic cesium lead halide perovskite (CsPbX₃, X = Cl, Br, I) is a promising material for developing novel electronic and optoelectronic devices. Despite the substantial progress that has been made in the development of large perovskite single crystals, the fabrication of high‐quality 2D perovskite single‐crystal films, especially perovskite with a low symmetry, still remains a challenge. Herein, large‐scale orthorhombic CsPbBr₃ single‐crystal thin films on zinc‐blende ZnSe crystals are synthesized via vapor‐phase epitaxy. Structural characterizations reveal a “CsPbBr₃(110)//ZnSe(100), CsPbBr₃[?110]//ZnSe[001] and CsPbBr₃[001]//ZnSe[010]” heteroepitaxial relationship between the covering CsPbBr₃ layer and the ZnSe growth substrate. It is exciting that the epitaxial film presents an in‐plane anisotropic absorption property from 350 to 535 nm and polarization‐dependent photoluminescence. Photodetectors based on the epitaxial film exhibit a high photoresponsivity of 200 A W^?1, a large on/off current ratio exceeding 10⁴, a fast photoresponse time of about 20 ms, and good repeatability at room temperature. Importantly, a strong polarization‐dependent photoresponse is also found on the device fabricated using the epitaxial CsPbBr₃ film, making the orthorhombic perovskite promising building blocks for optoelectronic devices featured with anisotropy.     

Determining the [001] crystal orientation of CdTe layers grown on (001) GaAs

We discuss various possibilities for determining the orientation of CdTe layers grown on (001) GaAs and in particular, determining the (001) orientation. This growth orientation is characterized by a three dimensional growth mechanism which controls the growth in the (111) orientation. We show that a thin layer of ZnTe deposited directly on the oxide free GaAs surface can be used to determine the (001) orientation, eliminate (111) phases and enhance a two dimensional growth of the CdTe layer, resulting in an improved crystalline quality and a smooth surface morphology. CdTe layers grown in the (111) direction on oxide free (001) GaAs substrates contain (111) microtwins and an intermixed (001) phase. This work is a part of a Ph.D. thesis to be submitted to the Weizmann Institute of Science.     

InP/InGaAs double-heterojunction bipolar transistors grown on (100)Si by metalorganic chemical vapor deposition

The authors report the successful fabrication of InP/InGaAs double-heterojunction bipolar transistors (DHBTs) grown by metalorganic chemical vapor deposition (MOCVD) on Si substrates. The Si substrates used were p-type (boron doped) FZ grown wafers with a resistivity of 5000 Ω×cm, oriented 2° off the (100) plane toward the [110] direction. Epitaxial layers for DHBTs were grown on the Si substrate with a thin GaAs buffer layer. A two-step growth process was applied for the InP layers on GaAs-on-Si wafers. The transistors exhibit high current gains over 200, which is comparable to those in transistors grown on InP substrates. The dislocations are found to increase the recombination current very little in the neutral base region, but increase in generation-recombination current at the emitter-base interface     

Ordering in InGaAs/InAlAs layers

The structure of InCaAs/InAlAs layers lattice matched to an InP substrate, grown on either (100) or on (110) with a 4° tilt toward [111] at 500 and 300°C has been investigated by transmission electron microscopy. High perfection resulted for the layers grown on [001] oriented substrates whereas growth on the near [110] substrates resulted in compositional nonuniformities, macrosteps formation, and ordering of the group III elements. This difference in structural perfection between the two sets of samples was also reflected in differences in electrical properties.     

Effect of Epilayer Tilt on Dynamical X-ray Diffraction from Uniform Heterostructures with Asymmetric Dislocation Densities

In this work we extend the dynamical theory of Bragg x-ray diffraction to account for a tilted, asymmetrically defected, uniform-composition epitaxial layer atop a (001) substrate. In a zincblende semiconductor there are eight active slip systems, within which two distinct types of dislocations exist. These two types are distinguished by their misfit segments, which are oriented along either the [110] or $[1\bar{1}0]$ direction. The two threading dislocation densities can be measured by observing the variation of the x-ray rocking curve width with the incident beam azimuth. However, the tilting of the epilayer also has a measurable and potentially conflicting effect on the rocking curve as a function of azimuth. First, the peak position varies by (nominally) twice the layer’s absolute tilt within a full azimuthal rotation. Second, the tilting of the layer affects the epilayer rocking curve width. Through use of the modified dynamical diffraction theory, we show that the peak width’s azimuthal dependence on tilt is of only second order, so that the layer misorientation with respect to the substrate need not be considered for the purpose of determining the two dislocation populations by x-ray diffraction. Dynamical simulations were performed and compared with experimental measurements for a ZnSe/GaAs(001) structure grown by photoassisted metalorganic vapor-phase epitaxy, and in this way the two dislocation density populations were found to be D _A = 1.6 × 10⁸ cm^?2 and D _B = 2.0 × 10⁸ cm^?2.     

［（Cdse）_m（ZnSe）_n］_p－Znse多量子阱中的多声子散射

对用原子层外延方法，在［００１］晶向ＧａＡｓ衬底上生长的［（Ｃｄｓｅ）ｍ（Ｚｎｓｅ）ｎ］ｐ－ＺｎＳｅ应变量子阱结构，在１０～３００Ｋ温度范围内测量了喇曼散射光谱，观察到两种类ＺｎＳｅＬＯ声子限制模．利用改变样品温度和入射光能量实现了共振喇曼散射，观察到高达７阶的类ＺｎＳｅＬＯ声子模．并讨论了多声子喇曼散射和热萤光过程的区别．     

Influence of Substrate Misorientation on the Composition and the Structural and Photoluminescence Properties of Epitaxial Layers Grown on GaAs(100)

The influence of the degree of misorientation and treatment of a GaAs substrate on the structural and optical characteristics of homoepitaxial GaAs/GaAs(100) structures grown by metal–organic chemicalvapor deposition is studied. From the data obtained by a series of structural and spectroscopic techniques, it is shown that the degree of deviation of the substrate from the exact orientation towards the [110] direction by an angle of up to 4° brings about stepwise growth of the GaAs film in the initial stage and a further increase in the degree of misorienration towards the [110] direction to 10° results in an increase in the number of structural defects in the epitaxial film. At the same time, the samples of homoepitaxial structures grown by metal–organic chemical-vapor deposition on GaAs(100) substrates misoriented by 4° towards the [110] direction possess the highest photoluminescence efficiency; it is ~15% higher than the corresponding quantity for structures grown on precisely oriented GaAs(100) substrates. Preliminary polishing of the GaAs substrate (removal of an oxide layer) also yields the intensification of photoluminescence emission compared to emission in the case of an unpolished substrate of the same type. For samples grown on substrates misoriented by 4°, such an increase in the photoluminescence efficiency is ~30%.     

Structure of CdTe(111)B grown by MBE on misoriented Si(001)

Single domain CdTe(111)B has been grown on Si(001) substrates tilted 1^o 2^o, and 4^o toward [110]. All the layers started with a double-domain structure, then a transition from a double- to a single-domain was observed by reflection high energy electron diffraction. A microscopic picture of this transition is presented. We also measured the tilt between CdTe(111)B and Si(001). The result does not follow the tilt predicted by the currently existing model. A new model of the microscopic mechanism of CdTe(111)B growth is presented. New evidence indicates that optimizing the tilt of the substrate surface is very crucial in improving the CdTe(111)B crystal quality.     

Evaluation of Zn{N[Si(CH3)3]2}2 as ap-type dopant in OMVPE growth of ZnSe

We have grown nominally undoped ZnSe on GaAs from the precursors H₂Se and Et₂Zn. Replacement of Et₂Zn by Zn[N(TMS)₂]₂ produced crystalline ZnSe of a lesser quality. Data indicate incorporation of nitrogen into the films when Et₂Zn is utilized as the main zinc source with Zn[N(TMS)₂]₂ being introduced at dopant levels. Characterization techniques employed include NMR, XRD, SIMS, SEM, PL, RGA, GC/MS, and Raman spectroscopy.     

Scanning force microscopy studies of GaAs films grown on offcut Ge substrates

The surface morphology of GaAs films grown on offcut Ge substrates is studied using a scanning force microscope (SFM). We investigated the effects of the Ge buffer layer, growth temperature, film thickness, and prelayer on the GaAs surface morphology. The starting Ge substrates are offcut 6° toward the [110] direction to minimize single steps on the substrates before molecular beam epitaxial film growth. We find that comparing with GaAs samples grown without Ge buffer layers or with unannealed Ge buffer layers, samples with annealed Ge buffer layers are much smoother and contain no antiphase boundaries (APBs) on the surface. For thick (≥1 μm) GaAs films with an annealed Ge buffer layer, the surfaces display crosshatch lines and elongated mounds (along , which are associated with the substrate offcut direction. As the film thickness increases, the crosshatch lines become shorter, denser and rougher, and the mounds grow bigger (an indication of GaAs homoepitaxial growth). We conclude that annealed Ge buffer layers are crucial for growing high quality GaAs films with few APBs generated during the growth. In addition, under optimal conditions, different prelayers make little difference for thick GaAs films with annealed Ge buffer layers.     

ZnSe heteroepitaxy on GaAs (110) substrate

ZnSe heteroepitaxial layers have been grown on GaAs (100), (110) on axis, and (110) 6° miscut substrates by molecular beam epitaxy. ZnSe on GaAs (110) shows smooth and featureless spectra from Rutherford backscattering channeling measurements taken along major crystalline directions, whereas ZnSe on GaAs (100) without pre-growth treatments exhibit large interface disorder in channeling spectra. ZnSe films grown on GaAs (110) on axis show facet formation over a wide range of growth conditions. The use of (110) 6° miscut substrates is shown to suppress facet formation; and under the correct growth conditions, facet-free surfaces are achieved. Etch pit density measurements give dislocation densities for ZnSe epitaxial layers grown on GaAs (100), (110) on axis, and (110) 6° miscut substrates of 10⁷/cm², 3 × 10⁵/cm² and 5 × 10⁴/cm², respectively. These results suggest that with further improvements to ZnSe growth on GaAs (110)-off substrates it may be possible to fabricate defect free ZnSe based laser devices.