Resistive Switching in Memristors Based on Ge/Si(001) Epitaxial Layers

Semiconductors - The Ag/Ge/Si(001) stacks with threading dislocations growing through the Ge epitaxial layers (ELs) manifested bipolar resistive switching (RS) between two metastable resistance...     

Comparison of MBE Growth of InSb on Si (001) and GaAs (001)

We describe the epitaxial growth of InSb films on both Si (001) and GaAs (100) substrates using molecular-beam epitaxy and discuss the structural and electrical properties of the resulting films. The complete 2 μm InSb films on GaAs (001) were grown at temperatures between 340°C and 420°C and with an Sb/In flux ratio of approximately 5 and a growth rate of 0.2 nm/s. The films were characterized in terms of background electron concentration, mobility, and x-ray rocking curve width. Our best results were for a growth temperature of 350°C, resulting in room-temperature mobility of 41,000 cm²/V s.  For the growth of InSb on Si, vicinal Si(001) substrates offcut by 4° toward (110) were used. We investigated growth temperatures between 340°C and 430°C for growth on Si(001). In contrast to growth on GaAs, the best results were achieved at the high end of the range of T _S =  C, resulting in a mobility of 26,100 cm²/V s for a 2 μm film. We also studied the growth and properties of InSb:Mn films on GaAs with Mn content below 1%. Our results showed the presence of ferromagnetic ordering in the samples, opening a new direction in the diluted magnetic semiconductors.     

A metal/Insulator/semiconductor (MIS) photocathode

A field-assisted photocathode based on the metal/alumina/ silicon (MAS) structure is described. Emission currents as large as 10 percent of the photoelectric current in the silicon have been demonstrated with spectral response only limited by the bandgap of the semiconductor. This suggests that MIS structures employing narrower band-gap semiconductors would be useful when response beyond 1 µm is desired. The MAS time response to a change in light is inversely proportional to the light level. Under illumination equivalent to moonlight (2 × 10¹¹absorbed photons/cm²/s) a time response of 4 s has been measured. In the simple planar structure described, charge spreading occurs in the inversion well. For imaging, a more complex structure is required.     

A Structural Investigation of CdTe(001) Thin Films on GaAs/Si(001) Substrates by High-Resolution Electron Microscopy

Epitaxial CdTe thin films were grown on GaAs/Si(001) substrates by metalorganic chemical vapor deposition using thin GaAs as a buffer layer. The interfaces were investigated using high-resolution transmission electron microscopy and geometric phase analysis strain mapping. It was observed that dislocation cores exist at the CdTe/GaAs interface with periodic distribution. The spacing of the misfit dislocation was measured to be about 2?nm, corresponding to the calculated spacing of a misfit dislocation (2.6?nm) in CdTe/Si with Burgers vector of a[110]/2. From these results, it is suggested that the GaAs buffer layer effectively absorbs the strain originating from the large lattice mismatch between the CdTe thin film and Si substrate with the formation of periodic structural defects.     

CoSi2薄膜与Si(001)界面的高分辨电子显微镜观察

利用高分辨透射电镜研究了经过550℃退火处理的共溅射CoSi2非晶结构薄膜与Si基体的界面.结果表明,550℃退火后薄膜已经发生晶化转变;同时CoSi2薄膜与Si基体发生反应扩散,在界面上生成了形状规则的CoSi2化合物,并与Si基体保持着相同的位向关系或孪晶位向关系.结合以上电镜观察,对这些界面化合物的生长机制进行了讨论.     

Stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells,grown on GaAs and Ge/Si(001) substrates

We report the observation of stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on Si(001) substrates with the application of a relaxed Ge buffer layer. Stimulated emission is observed at 77 K under pulsed optical pumping at a wavelength of 1.11 μm, i.e., in the transparency range of bulk silicon. In similar InGaAs/GaAsSb/GaAs structures grown on GaAs substrates, room-temperature stimulated emission is observed at 1.17 μm. The results obtained are promising for integration of the structures into silicon-based optoelectronics.     

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.     

MBE In_xGa_(1-x)As/GaAs(001)系统晶格失配的研究

本文利用X射线双晶衍射和电子探针显微分析方法,研究了MBE In_xGa_(1-x)As/GaAs(001)系统的晶格失配与In含量x值的关系.在外延层厚度t_(?)～2μm的情况下,获得范性应变临界组份x_c=0.114.当xx_c时,外延层出现范性形变.     

GaN/GaAs(001)外延薄膜的湿法腐蚀特性

对在GaAs (001) 衬底上用金属有机物气相外延(MOVPE)方法生长的GaN薄膜的湿法腐蚀特性进行了研究.所用腐蚀液包括HCl、H3PO4、KOH水溶液以及熔融KOH,腐蚀温度为90～300℃.实验发现不同的腐蚀液在样品表面腐蚀出不同形状的腐蚀坑.KOH溶液腐蚀出长方形的坑,长边平行于(111)A面,表明沿相互垂直的〈110〉晶向的腐蚀特性不同.用不同晶面相对反应性的差别定性解释了腐蚀的这种非对称性.此外,还发现KOH水溶液更有可能用于显示立方相GaN外延层中的层错.     

Interfacial reactions of cobalt thin films on (001) GaAs

Interfacial reactions between cobalt thin films and (001) GaAs have been studied by transmission electron microscopy, energy-dispersive analysis of x-rays in a scanningTEM, Auger electron spectroscopy and x-ray photoelectron spectroscopy. The completely reacted layer was found to be “β-Ga₂0₃/(CoGa, CoAs)/GaAs.” The formation of a surface layer ofβ-Ga₂O₃ and the use of encapsulated samples minimized As loss from the reacted layer. Both CoGa and CoAs were found to grow epitaxially on (001) GaAs. The orientation relationships between CoGa and GaAs were determined to be [001] CoGa//[001] GaAs and (220) CoGa//(220) GaAs. The Burgers vectors of interfacial dislocations were identified as 1/2 〈101〉 and 1/2 〈011〉 which are inclined to the (001) GaAs surface. Almost all of the CoGa films were found to be epitaxially related to the surface. No interfacial dislocations were observed in most of the epitaxial CoAs films which are considered to be pseudomorphic with respect to GaAs. The orientation relationships between CoAs and GaAs were determined to be [101] CoAs//[011] GaAs and (020) CoAs//(220) GaAs. Two-step annealing was found to be effective in promoting epitaxial growth.     

The interactions between Si/Co films and GaAs(001) substrates

Interfacial reactions of Si/Co films on (001) oriented GaAs substrate, in the temperature range 300–700°C for 30 min, have been investigated using a combination of x-ray diffraction, Auger electron spectroscopy, and transmission electron microscopy. Cobalt starts to react with GaAs and Si at 380°C by formation of Co₂GaAs, and Co₂Si phases, respectively. At 420°C, the entire layer of Co is consumed, and the layer structure is observed with the sequence Si/CoSi/CoGa(CoAs)/Co₂GaAs/GaAs. Contacts produced in this annealing regime are rectifying and the Schottky barrier heights increase from 0.69 eV(as-deposited state) up to 0.81 eV (420°C). In the subsequent reaction, CoSi grows at the expense of the decompositions of CoGa and CoAs at 460°C. In addition, the ternary phase also is decomposed and only the CoSi phase remains upon the GaAs surface at 600°C. Contacts produced at higher temperature regime (>460°C) have low barriers. The interface between CoSi and GaAs is stable up to 700°C. The results of interfacial reactions can be understood from the calculated Si−Co−Ga−As quaternary phase diagram.     

GaN/GaAs(001)外延薄膜的湿法腐蚀特性

对在GaAs (001) 衬底上用金属有机物气相外延(MOVPE)方法生长的GaN薄膜的湿法腐蚀特性进行了研究.所用腐蚀液包括HCl、H3PO4、KOH水溶液以及熔融KOH,腐蚀温度为90～300℃.实验发现不同的腐蚀液在样品表面腐蚀出不同形状的腐蚀坑.KOH溶液腐蚀出长方形的坑,长边平行于(111)A面,表明沿相互垂直的〈110〉晶向的腐蚀特性不同.用不同晶面相对反应性的差别定性解释了腐蚀的这种非对称性.此外,还发现KOH水溶液更有可能用于显示立方相GaN外延层中的层错.     

Electron mobility anisotropy in (Al,Ga)Sb/InAs two-dimensional electron gases epitaxied on GaAs (001) substrates

The electron mobility anisotropy in (Al,Ga)Sb/InAs two-dimensional electron gases with different surface morphology has been investigated. Large electron mobility anisotropy is found for the sample with anisotropic morphology, which is mainly induced by the threading dislocations in the InAs layer. For the samples with isotropic morphology, the electron mobility is also anisotropic and could be attributed to the piezoelectric scattering. At low temperature (below transition temperature), the piezoelectric scattering is enhanced with the increase of temperature, leading to the increase of electron mobility anisotropy. At high temperature (above transition temperature), the phonon scattering becomes dominant. Because the phonon scattering is isotropic, the electron mobility anisotropy in all the samples would be reduced. Our results provide useful information for the comprehensive understanding of electron mobility anisotropy in the (Al,Ga)Sb/InAs system.     

Domain epitaxial growth of TiN/Si(001), TiN/GaAs(001), and Si/TiN/Si(001) heterostructures by laser physical vapor deposition: Theory and experiment

We have successfully deposited epitaxial titanium nitride films on (001) silicon and (001) gallium arsenide substrates and multilayer Si/TiN/Si(001) epitaxial heterostructures using pulsed laser (KrF: λ = 248 nm, τ = 25 ns) physical vapor deposition. The deposition of TiN was carried out at a substrate temperature of 600°C on Si(001) and 400°C on GaAs(00l). The interfaces were sharp without any indication of interfacial reaction. The epitaxial relationships were found to be <001> TiN ‖<001> Si on the silicon substrate, <001> Si ‖<001> TiN |<001> Si on the heterostructure, and [1-10] TiN‖[110] GaAs and [001] TiN ‖[110] GaAs on the GaAs substrate. The growth in these large-mismatch systems is modeled and the various energy terms contributing to the growth of these films are determined. The domain matching epitaxy provides a mechanism of epitaxial growth in systems with large lattice mismatch.The epitaxial growth is characterized by domain epitaxial orientation relationships with m lattice constants of epilayer matching with n of the substrate and with a small residual domain mismatch present in the epilayer. This residual mismatch is responsible for a coherent strain energy. The magnitude of compression of Ti-N bond in the first atomic layer, contributing to the chemical free energy of the interface during the initial stages of growth, is found to be a very important factor in determining the orientation relationship. This result was used to explain the differences in the orientaion relationships between TiN/Si and TiN/GaAs systems. The various energy terms associated with the domain epitaxial growth are evaluated to illustrate that the domain epitaxial growth is energetically favorable compared to the lattice mismatched epitaxial growth. The results of this analysis illustrate that the observed variations in the epitaxial growth are consistent with the minimum energy configurations associated with the domain epitaxial growth.     

Molecular-Beam Epitaxy of Two-Dimensional GaSe Layers on GaAs(001) and GaAs(112) Substrates: Structural and Optical Properties

Semiconductors - The results of studies of the structural and optical properties of two-dimensional GaSe layers grown by molecular-beam epitaxy on GaAs(001) and GaAs(112) substrates using a valve...     

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.     

快速率生长MBE InAs/GaAs(001)量子点

用快速率(1.0ML/s)生长MBE InAs/GaAs(001)量子点。原子力显微镜观察结果表明,在量子点体系形成的较早阶段,量子点密度N(θ)随InAs沉积量θ的变化符合自然指数形式N(θ)∝ek(θ-θc),这与以前在慢速生长(≤0.1ML/s)条件下出现的标度规律N(θ)∝(θ-θc)α明显不同。另外,在N(θ)随θ增加的过程中,快速率生长量子点的高度分布没有经历量子点平均高度随沉积量θ逐渐增加的过程。这些实验观察说明,以原子在生长表面作扩散运动为基础的生长动力学理论至少是不全面的,不适用于解释InAs量子点的形成。这些观察和讨论说明,即使在1.0ML/s的快速率生长条件下,量子点密度也可以通过InAs沉积量有效地控制在1.0×108cm-2以下,实现低密度InAs量子点体系的制备。