Influence of elastic strains in sublayers on the critical thickness of the Stranski-Krastanow transition for the GeSi/Si(001) system

A novel estimation of the critical thickness of the epitaxial layer in the Stranski-Krastanow (SK) transition is proposed. The transition criterion is based on accumulation of the energy of the effective strain up to a certain critical value. The calculation includes the elastic energy stored in elastically strained layers, takes into account the restriction on the depth of the strained layer still affecting the transition, and a segregation effect described by thermally activated atomic exchange. The equations of growth on the vicinal substrate surface that divide each monolayer into submonolayers parallel to the surface are used. Simulation results are compared with the corresponding experimental data for the heterostructures built of a strained sublayer covered by a spacer layer on which a wetting layer is deposited until the SK transition occurs. The Ge/Si structures of this type are grown by molecular beam epitaxy, and in addition, the experimental results for InAs/GaAs systems, published in the literature, are used. A comparison of experimental and calculated data on the dependence between the critical thickness of the wetting layer and the thickness of the spacer layer shows good agreement for both Ge/Si and InAs/GaAs systems.     

Epoxy bond and stop-etch (EBASE) technique enabling backside processing of (Al)GaAs heterostructures

The epoxy bond and stop-etch (EBASE) technique enables both the frontside and the backside processing of very thin (3000Å) GaAs/AlGaAs epitaxial layer structures. Using this technique, a conventionally processed epitaxial layer structure is inverted and epoxied to a new host substrate. The original substrate is removed leaving only the original epitaxial structure expoxied to the host substrate. The exposed backside of the epitaxial structure may then be processed. Because the structures fabricated using this technique are so thin, mesas, Schottky gates, and ohmic contacts may be defined in close proximity both above and below the active device layers.     

AlGaN/GaN heterostructure grown on 1 -tilt sapphire substrate by MOCVD

AlGaN/GaN epitaxial layers were grown on 0^°-tilt and 1^°-tilt sapphire substrates by metalorganic chemical vapor deposition (MOCVD). With exactly the same growth conditions, it was found that dislocation density was smaller and crystal quality was better for the AlGaN/GaN epitaxial layers prepared on 1^°-tilt sapphire substrate. We also found that AlGaN/GaN epitaxial layers on 1^°-tilt sapphire substrate were grown with step growth mode while those on 0^°-tilt substrate were grown with two-dimensional island growth. From the temperature-dependent mobility, it was found that crystal quality of the AlGaN/GaN epitaxial layer prepared on 1^°-tilt sapphire substrate is better.     

Surface preparation effect of GaAs(110) substrates on the ZnSe epitaxial layer grown by molecular beam epitaxy

The effect of the surface preparation of the GaAs(110) substrate on the ZnSe epitaxial layer grown by molecular beam epitaxy (MBE) was investigated by means of etch-pit density (EPD) measurements, surface morphology observation, and reflection high-energy electron diffraction (RHEED) analysis. The ZnSe epitaxial layer grown on a GaAs(110) surface prepared by cleaving the (001)-oriented wafer in ultrahigh vacuum (UHV) showed about 5×10⁴ cm^-2 of EPD. This value is much lower than that observed from both the samples grown on the mechanically polished surface with and without a GaAs buffer layer. Due to the non-stoichiometric surface after thermal evaporation of the surface oxide, three-dimensional growth can easily occur on the mechanically polished GaAs(110) substrate. These results suggest that the stoichiometric and atomically flat substrate surface is essential for the growth of low-defect ZnSe epitaxial layers on the GaAs(110) non-polar surface. Received: 21 August 1998 / Accepted: 19 October 1998 / Published online: 28 April 1999     

Ensembles of indium phosphide nanowires: physical properties and functional devices integrated on non-single crystal platforms

A new route to grow an ensemble of indium phosphide single-crystal semiconductor nanowires is described. Unlike conventional epitaxial growth of single-crystal semiconductor films, the proposed route for growing semiconductor nanowires does not require a single-crystal semiconductor substrate. In the proposed route, instead of using single-crystal semiconductor substrates that are characterized by their long-range atomic ordering, a template layer that possesses short-range atomic ordering prepared on a non-single-crystal substrate is employed. On the template layer, epitaxial information associated with its short-range atomic ordering is available within an area that is comparable to that of a nanowire root. Thus the template layer locally provides epitaxial information required for the growth of semiconductor nanowires. In the particular demonstration described in this paper, hydrogenated silicon was used as a template layer for epitaxial growth of indium phosphide nanowires. The indium phosphide nanowires grown on the hydrogenerated silicon template layer were found to be single crystal and optically active. Simple photoconductors and pin-diodes were fabricated and tested with the view towards various optoelectronic device applications where group III–V compound semiconductors are functionally integrated onto non-single-crystal platforms.     

Formation of oriented rodlike nickel silicide precipitates during magnetron deposition of carbon and nickel on silicon

Formation of rodlike structures elongated in the 〈100〉 and 〈010〉 directions of silicon crystal was observed during magnetron codeposition of carbon and nickel on (100) silicon substrate with a natural oxide layer. Rodlike structures did not form during deposition in similar conditions on (111) silicon substrate. It has been revealed that the rodlike structures represent epitaxial nickel silicide precipitates. The results of experimental study of the composition, structure, and shape of forming silicide clusters as a function of the silicon substrate orientation and the codeposited layer thickness are presented.     

MBE-grown Si: Er light-emitting structures: Effect of epitaxial growth conditions on impurity concentration and photoluminescence

The technology and properties of light-emitting structures based on silicon layers doped by erbium during epitaxial MBE growth are studied. The epitaxial layer forming on substrates prepared from Czochralski-grown silicon becomes doped by oxygen and carbon impurities in the process. This permits simplification of the Si: Er layer doping by luminescence-activating impurities, thus eliminating the need to make a special capillary for introducing them into the growth chamber from the vapor phase. The photoluminescence spectra of all the structures studied at 78 K are dominated by an Er-containing center whose emission line peaks at 1.542 μm. The intensity of this line measured as a function of the substrate and erbium dopant source temperatures over the ranges 400–700°C and 740–800°C, respectively, exhibits maxima. The edge luminescence and the P line observed in the PL spectra are excited predominantly in the substrate. The erbium atom concentration in the epitaxial layers grown at a substrate temperature of 600°C was studied by Rutherford proton backscattering and exhibits an exponential dependence on the erbium source temperature with an activation energy of ～2.2 eV.     

Growth of magnetic materials and structures on Si(0 0 1) substrates using Co2Si as a template layer

We report in this paper the use of Co₂Si silicide as a template layer for the integration of magnetic materials and structures on silicon substrate. By undertaking Co deposition on silicon at a temperature of about 300 °C, we show that it is possible to obtain a smooth and epitaxial Co₂Si layer, which can act as a template layer preventing the reaction between Co and other transition metals with silicon. Two examples of over-growth of magnetic materials and structures on this template layer will be presented: growth of ferromagnetic Co layers and of magnetic tunnel junctions (Co(Fe)/AlO_x/NiFe).     

Addimer chain structures: Metastable precursors to island formation on Ge-Si(0 0 1)-(2 × n) alloyed surface

We have identified addimer chain structures as metastable precursors to compact epitaxial islands on the (2 × n) reconstructed SiGe wetting layer, using polarity-switching scanning tunneling microscopy (STM). These chain structures are comprised of 2-12 addimers residing in the troughs of neighboring substrate dimer rows. The chain structures extend along equivalent 〈1 3 0〉 directions across the substrate dimer rows in a zigzag fashion, giving rise to kinked and straight segments. We measure a kink-to-straight ratio of nearly 2:1. This ratio corresponds to a free energy difference of 17 ± 4 meV, favoring the formation of kinked segments. The chain structures convert to compact epitaxial islands at elevated temperatures (?90 °C). This conversion suggests that the chain structures are a precursor for compact island formation on the SiGe wetting layer. We digitally process filled- and empty-state STM images to distinguish chain structures from compact islands. By monitoring the populations of both species over time, the chain-to-island conversion rates are measured at substrate temperatures ranging from 90 to 150 °C. The activation energy for the conversion process is measured to be 0.7 ± 0.2 eV with a corresponding pre-exponential factor of 5 × 10^4±2 s⁻¹.     

Characterization of MOVPE-grown GaAs layers by C-V analysis

A computer simulation study of the capacitance of a surface space charge layer in undoped n-GaAs grown by metalorganic vapour phase epitaxy is presented. The effect of the deep donor level EL2 on the surface capacitance of epilayers with an ideal free surface is estimated. In order to approach the as-grown layer surface the model used is extended considering MIS and Schottky-barrier structures and their voltage-capacitance curves are analysed. The theoretical C-V dependences are compared with experimental C-V curves of a real structure including N⁺-GaAs substrate, undoped n-GaAs epitaxial layer containing EL2 levels and thin native oxide. Conditions are determined at which the EL2 levels as well as the native oxide film may influence the capacitance characteristics.     

在6H-SiC衬底上用低压MOVPE法生长AlN和GaN的过程中用(AlN/GaN)多层缓冲层来控制残余应力

人们已提出用BAlGaN四元系材料制备紫外光谱区的光发射器件.GaN和AlN二元系是这种四元材料在器件应用中的基础材料.6H-SiC衬底在氮化物生长中因其晶格失配小是一大优势,而且SiC衬底的热膨胀系数也和AlN的很接近.然而,对于AlN外延层来说,需要控制其中的残余应力,因为在SiC衬底上直接生长的AlN外延层中存在着因晶格失配所产生的压缩应力.另一方面,在SiC衬底上直接生长的GaN外延层中存在着拉伸应力.这种拉伸应力起源于GaN比衬底有着更大的热膨胀系数.本文讨论了在6H-SiC衬底上生长的氮化物外延层中残余应力的类型、数量及控制.为此目的,提出了在6H-SiC衬底上,无论是生长AlN,还是生长GaN,都可以采用(GaN/AlN)多层缓冲层的办法,作为控制残余应力的有效方法.我们还讨论了AlN和GaN外延层的结晶质量和残余应力间的关系.     

椭圆偏振光谱表征单晶硅衬底上生长的非晶硅和外延硅薄膜

本文采用射频等离子体增强化学气相沉积(rf-PECVD)技术在单晶硅衬底上沉积了两个系列的硅薄膜. 通过对样品进行固定角度椭圆偏振测试, 结果表明第一个系列硅薄膜为非晶硅, 形成了突变的a-Si:H/c-Si异质结构, 此结构在HIT电池中有利于形成好的界面特性, 对于非晶硅薄膜采用通常的Tauc-Lorentz摇摆模型(Genosc)拟合结果很好; 第二个系列硅薄膜为外延硅, 对于外延硅薄膜, 随着膜厚增加晶化率降低, 当外延硅薄膜厚度为46 nm时开始非晶硅生长. 对于外延硅通常采用EMA模型(即将硅薄膜体层看成由非晶硅和c-Si构成的混合层)拟合结果较好, 当硅薄膜中出现非晶硅生长时, 将体层分成混合层和非晶硅两层, 采用三层模型拟合结果很好. 本文证实了椭偏光谱分析采用不同的模型可对单晶硅衬底上不同结构的硅薄膜进行有效表征.     

Influence of growth conditions on the surface quality and structural perfection of multicomponent heterostructures based on group A3B5 compounds

The surface quality of epitaxial multicomponent layers based on group A³B⁵ compounds, which are grown under different conditions via floating-zone refining with a temperature gradient, is comprehensively analyzed. The main parameters (temperature gradient, solution-melt composition, supercooling level, matching between lattice parameters and the thermal expansion coefficients of the layer and substrate, and substrate orientation) affecting the surface quality and structural perfection of the heterostructures are determined.     

硅基低位错密度厚锗外延层的UHV/CVD法生长

利用超高真空化学气相淀积系统, 基于低温缓冲层和插入应变超晶格的方法, 在Si(100)衬底上外延出厚度约为880 nm的纯Ge层. 采用X射线双晶衍射、高分辨透射电镜、原子力显微镜和光致发光谱分别表征了其结构及光学性质. 测试结果显示外延Ge的X射线双晶衍射曲线半高宽为273", 表面均方根粗糙度为0.24 nm, 位错密度约为1.5×10⁶ cm². 在室温下观测到外延Ge的直接带跃迁光致发光, 发光峰值位于1540 nm. 表明生长的Si基Ge材料具有良好的结晶质量, 可望在Si基光电子器件中得到应用.     

Characterisation of the interface between GaAs: Cr substrates andn-type epitaxial GaAs layers by infrared multiple interference analysis

Infrared reflectivity measurements on vapour phase grownn-GaAs epitaxial layers (n=7×10¹⁶...5×10¹⁸ cm^–3) deposited on semi-insulating GaAs:Cr substrates show interference structures whose strength cannot be explained by the interference pattern of a simple two layer system. Assuming a third very thin (0.4 m) interfacial layer it is possible to describe the experimental results. For Te doping the carrier concentration in the interfacial film is higher than in the volume of the epitaxial layer; it is lower for Sn doping. The results of this nondestructive optical method were confirmed by conductivity measurements while etching the sample. The origin of the interfacial layer is discussed in terms of non-steady state conditions at the beginning of the epitaxial growth.     

SiO2对多层GaN外延片热应力分布影响的仿真分析

为了研究SiO2对多层结构GaN外延片的热应力的影响,以直径d为40 mm的GaN外延片为研究对象,利用有限元分析法分别对蓝宝石/AlN/GaN和蓝宝石/SiO2/AlN/GaN这两种光阴极组件外延片表面热应力进行理论计算和仿真。在其他结构参数相同的情况下,分别分析了两种光阴极组件外延片径向和厚度方向的应力分布,分析了外延片热应力分布及影响因素。分析结果显示:在1 200 ℃的生长温度下,径向区域内的热应力分布比较均匀,厚度方向的热应力均在衬底和外延层的界面上发生突变。最后分析了外延片生长温度、蓝宝石衬底和GaN、AlN过渡层厚度对表面热应力的影响。     

Rotational epitaxy of a hexagonal layered material on a square substrate: PbI2 on InSb(001)

PbI₂ has been adsorbed on the clean InSb(001)-(4 × 1) reconstructed surface and on the InSb(001)-(1 × 3)-Pb lead covered reconstructed surface. On the clean surface epitaxial growth occurred with the unit mesh of the layered PbI₂ aligning exactly with both the substrate [110] and [1 0] directions. On desorption a reaction occurred between the last layer of PbI₂, and the substrate, forming a series of structures which finished with a well-formed (1 × 3)-Pb structure in which the surface is depleted/enriched in In/Sb compared to the clean (4 × 1). The Pb in this structure is thought to partially replace surface In. Epitaxial adsorption also occurred on the (1 × 3)-Pb surface generating a single, well-formed structure with the hexagonal net of the PbI₂ aligned with just the [1 0] substrate direction. The structures and reactions are discussed and a row matching model is proposed to explain the single epitaxial orientation of PbI₂ on the (1 × 3)-Pb surface.     

Evolution of topological order in Xe films on a quasicrystal surface

We report results of the first computer simulation studies of a physically adsorbed gas on a quasicrystalline surface Xe on decagonal Al-Ni-Co. The grand canonical Monte Carlo method is employed, using a semiempirical gas-surface interaction, based on conventional combining rules, and the usual Lennard-Jones Xe-Xe interaction. The resulting adsorption isotherms and calculated structures are consistent with the results of LEED experimental data. The evolution of the bulk film begins in the second layer, while the low coverage behavior is epitaxial. This transition from epitaxial fivefold to bulklike sixfold ordering is temperature dependent, occurring earlier (at lower coverage) for the higher temperatures.     

Transport properties of epitaxial graphene formed on the surface of a metal

The transport properties of epitaxial graphene formed on the surface of a metal substrate have been considered within the approach based on the model Anderson-Newns Hamiltonian. An analytical expression for the density of states of epitaxial graphene has been obtained and the renormalization of the Fermi velocity in doped epitaxial graphene has been investigated. The real part of the dynamic conductance of epitaxial graphene has been examined and the limiting values of conductance have been analyzed. When there is no interaction between the graphene and the substrate, the static conductance of epitaxial graphene takes on the universal value 2e ²/π² ?. The fundamental problems considered in this study are of crucial importance in the study of optical, magneto-optical, thermoelectric, and thermomagnetic properties of epitaxial graphene. The obtained results are of great interest for practical use of epitaxial graphene as a promising material for microwave technology.     

Study on structural properties of epitaxial silicon films on annealed double layer porous silicon

In this paper, epitaxial silicon films were grown on annealed double layer porous silicon by LPCVD. The evolvement of the double layer porous silicon before and after thermal annealing was investigated by scanning electron microscope. X-ray diffraction and Raman spectroscopy were used to investigate the structural properties of the epitaxial silicon thin films grown at different temperature and different pressure. The results show that the surface of the low-porosity layer becomes smooth and there are just few silicon-bridges connecting the porous layer and the substrate wafer. The qualities of the epitaxial silicon thin films become better along with increasing deposition temperature. All of the Raman peaks of silicon films with different deposition pressure are situated at 521 cm⁻¹ under the deposition temperature of 1100 °C, and the Raman intensity of the silicon film deposited at 100 Pa is much closer to that of the monocrystalline silicon wafer. The epitaxial silicon films are all (4 0 0)-oriented and (4 0 0) peak of silicon film deposited at 100 Pa is more symmetric.