Low-temperature Si epitaxy on large-grained polycrystalline seed layers by electron–cyclotron resonance chemical vapor deposition

The epitaxial thickening of polycrystalline Si films on glass substrates is of great interest for the realization of crystalline Si thin film solar cells and other large-area thin film devices. In this paper we report on the epitaxial growth of Si at temperatures below on polycrystalline seed layers using electron–cyclotron resonance chemical vapor deposition. The Si seed layers were prepared by aluminum-induced crystallization. The quality of the ECRCVD-grown films strongly depends on the orientation of the underlying seed layer grains. Due to a mainly favorable orientation of the seed layers more than 73% of the substrate area were epitaxially thickened. It turned out that a (1 0 0) preferential orientation is favorable for epitaxial thickening. This, however, is not the only requirement for successful low-temperature epitaxial growth of Si.     

Electron microscopy studies of epitaxial MgB2 superconducting thin films grown by in situ reactive evaporation

The morphology and chemistry of epitaxial MgB₂ thin films grown using reactive Mg evaporation on different substrates have been characterized by transmission electron microscopy methods. For polycrystalline alumina and sapphire substrates with different surface planes, an MgO transition layer was found at the interface region. No such layer was present for films grown on MgO and 4-H SiC substrates, and none of the MgB₂ films had any detectable oxygen incorporation nor MgO inclusions. High-resolution electron microscopy revealed that the growth orientation of the MgB₂ thin films was closely related to the substrate orientation and the nature of the intermediary layer. Electrical measurements showed that very low resistivities (several μΩ cm at 300 K) and high superconducting transition temperatures (38 to 40 K) could be achieved. The correlation of electrical properties with film microstructure is briefly discussed.     

Study of ZnSe and CdSe thin film epitaxy on germanium and silicon substrates

The parameters of vaporization, mass-transfer, condensation, and epitaxial growth by hot wall technique (HWT) of ZnSe and CdSe thin films on monocrystalline Ge and Si substrates are studied (Bubnov et al.). It is shown, that the layers structure is improved as the mass transfer mechanism approaches to gasodinamical vapor flow. The influence of condensation temperature of the layers on their crystallographic structure is shown. The increase of the temperature gradient from the source towards the substrate as well as the substrate temperature conditions for growing layers of hexagonal modification. The decrease of the temperature gradient leads to cubic modification. The electron diffraction study revealed the stepwise character of the zinc selenide and cadmium selenide film growth. The knowledge of the parameters of ZnSe and CdSe thin films on monocrystalline Ge and Si by hot wall technique at relatively low substrate temperatures allows to obtain layers, suitable for formation of solid state devices for registration and reflection of optical information.     

Crystalline Properties of Strontium Barium Niobate Thin Films Produced by Pulsed Laser Deposition

Highly oriented strontium barium niobate (SBN) thin films have been grown on MgO {100}substrates by pulsed laser deposition. The films have been characterised by X-ray diffraction (XRD), scanning electron microscopy and atomic force microscopy. XRD theta - 2 theta scans indicate that the single phase crystalline SBN layers with the {001} orientation perpendicular to the plane of the substrate . Because of the difference between the thermal expansion coefficients of the SBN thin film and the MgO {100} substrate, it is necessary to adapt a slow cooling rate after deposition to retain the highly oriented SBN thin film on the substrate. The presence of non-uniform residual strain in SBN thin film has been analysed from broadening of the (00l) SBN film diffraction lines. The influence of oxygen partial pressure on the crystalline properties of SBN thin films have also been investigated.     

Atomistic examinations of the solid-phase epitaxial growth of silicon

The low-temperature vapor deposition of silicon thin films and the ion implantation of silicon can result in the formation of amorphous silicon layers on a crystalline silicon substrate. These amorphous layers can be crystallized by a thermally activated solid-phase epitaxial (SPE) growth process. The transformations are rapid and initiate at the buried amorphous to crystalline interface within the film. The initial stages of the transformation are investigated here using a molecular dynamics simulation approach based upon a recently proposed bond order potential for silicon. The method is used first to predict an amorphous structure for a rapidly cooled silicon melt. The radial distribution function of this structure is shown to be similar to that observed experimentally. Molecular dynamics simulations of its subsequent crystallization indicate that the early stage, rate limiting mechanism appears to be removal of tetrahedrally coordinated interstitial defects in the nominally crystalline region just behind the advancing amorphous to crystalline transition front. The activation barriers for this interstitials migration within the bulk crystal lattice are calculated and are found to be comparable to the activation energy of the overall solid-phase epitaxial growth process simulated here.     

Theoretical stress calculations in polar,semipolar and nonpolar AlGaN/GaN heterostructures of different compositions

The new comprehensive model of the process for matching epitaxial layers to substrates, in dependence of theirs crystallographic orientation, was developed to allow a theoretical prediction of the strain and stress in thin AlGaN epitaxial layers with different composition grown on GaN template. The elements of the continuous anisotropic materials strength theory was applied to develop the model. It was observed that in AlGaN/GaN heterostructures the stress was greater than the upper limit of acceptable tensile stress even for a small Al content and also that the stress could greatly vary, in a value and a direction, depending on substrate crystallographic orientation and an Al content in AlGaN layer. The obtained results theoretically explained the commonly observed technological problems occurring during the growth of AlGaN layers even with a small Al content.     

Characterization of silicon layers epitaxially grown on metallurgical-grade polycrystalline substrates

The structural and electrical properties of silicon layers epitaxially grown on metallurgical-grade polycrystalline silicon substrates are examined to clarify the effect of grain boundaries, crystal defects and impurities in the substrates. Chemical etching of the epitaxial layer reveals that all the grain boundaries continue from the substrate into the epitaxial layer, whereas lines of high density etch pits do not always continue. The polycrystalline thin film solar cells are fabricated on the metallurgical-grade silicon substrates by successive deposition of p and n⁺ layers. These cells show short circuit current densities around 70% of that of the conventional single crystal cell. This reduction of the short circuit current is caused mainly by the short minority carrier diffusion length in the grains probably due to impurities involved in the epitaxial layers. The origins of such impurities are discussed by considering autodoping and solid-state diffusion from the substrate during growth of epitaxial layers.     

沉积温度对磁控溅射BiFeO3薄膜结构和性能的影响

应用磁控溅射法在以SrRuO3 (SRO)薄膜为缓冲层的Pt/TiO2/SiO2/Si(001)基片上制备了多晶BiFeO3 (BFO)薄膜,构架了SRO/BFO/SRO异质结电容器.采用X射线衍射、铁电测试仪等研究沉积温度对BFO薄膜结构和性能的影响.X射线衍射图谱显示BFO薄膜为多晶结构.在2.5 kHz测试频率下,500℃生长的BFO薄膜呈现比较饱和的电滞回线,2Pr为145μC/cm2,矫顽场Ec为158 kV/cm,漏电流密度约为2.4×104 A/cm2.漏电机制研究表明,在低电场区,SRO/BFO/SRO电容器满足欧姆导电机制,在高电场区,满足普尔-弗兰克导电机理.实验发现:SRO/BFO/SRO电容器经过109翻转后仍具有良好的抗疲劳特性.     

Epitaxial growth of ZnO films

After summing up the main physical properties of ZnO and its subsequent applications the aim of this article is to review the growth of ZnO epitaxial films by PLD, MBE, MOCVD and sputtering under their various aspects, substrates, precursors, reaction chemistry, assessment of the layers etc. …, keeping constantly in mind some key issues for the device applications of ZnO in optoelectronics, surface acoustic filters and spintronics, amongst which the growth of high quality epitaxial layers of both n- or p-type conductivity, the possibility of dissolving transition elements in the layers, the growth of ZnO related alloys and heterostructures are of major significance.     

Selective epitaxy and lateral overgrowth of 3C-SiC on Si – A review

This review article attempts to present a comprehensive picture of the progress in selective epitaxial growth (SEG) of cubic silicon carbide (3C-SiC) to make it a cheap and practical material for high temperature and high power, high frequency and MEMS (Micro Electromechanical Systems) applications. Selective epitaxial growth followed by epitaxial lateral overgrowth (ELO) is a suitable approach to minimize the interfacial defects and other planar defects in case of thin film growth. Different techniques of SEG and its application to Si, GaAs and III–V nitrides are reviewed briefly in the first section of this article. Various SEG techniques like epitaxial lateral overgrowth, pyramidal growth and pendeo epitaxial growth, etc. have been discussed extensively for growing 3C-SiC on Si, together with the characterization of the grown films. The influence of various experimental parameters such as temperature of growth, choice of mask material, influence of an etchant, pattern shape and size, etc. is also discussed. On the basis of these data, it is believed that SEG and related techniques are a promising approach for heteroepitaxial growth of 3C-SiC films useful for devices and MEMS applications.     

气相输运沉积制备c轴择优取向的碘化铋薄膜

铋基卤化物材料因其无毒和优良的光电性能而显示出巨大的应用潜力。BiI₃作为一种层状重金属半导体,已被用于X射线检测、γ射线检测和压力传感器等领域,最近其作为一种薄膜太阳能电池吸收材料备受关注。本文采用简单的气相输运沉积(VTD)法,以BiI₃晶体粉末作为蒸发源,在玻璃基底上得到高质量c轴择优取向的BiI₃薄膜。并通过研究蒸发源温度和沉积距离对薄膜物相和形貌的影响,分析了BiI₃薄膜择优生长的机理。结果表明VTD法制备的BiI₃薄膜属于三斜晶系,其光学带隙为~1.8 eV。沉积温度对薄膜的择优取向有较大影响,在沉积温度低于270 ℃时,沉积的薄膜具有沿c轴择优取向生长的特点,超过此温度,c轴择优取向生长消失。在衬底温度为250 ℃、沉积距离为15 cm时制备的薄膜结晶性能最好,晶体形貌为片状八面体。     

Synthesis and epitaxial growth of CdTe films by neutral and ionized beams

The growth of CdTe thin films has been studied by epitaxial processes on the cleavage surface of rock salt in vacuum, using electron microscopic and electron diffraction techniques. The crystallinity and structure of the films depend largely upon the intensities and species of the incident beams. The use of two beams effused separately from the Knudsen cells resulted in the growth of films of good crystallinity when the intensity ratio N_Cd : N_Te was 10 : 1. The epitaxial relationships were studied over the range of substrate temperatures between room temperature and 350°C. The co-existence of α-hexagonal and β-cubic modifications of CdTe and their proportions in the film were revealed as a function of the growth processes and substrate temperature. If two beams were ionized by electron bombardment inside the cells and were incident upon the substrate by applying a dc voltage between source and substrate, the epitaxial temperature can be lowered to near room temperature, giving good epitaxy. The epitaxial relationships in the CdTe/NaCl system have been studied.     

Real structure of the ZnO epitaxial films on (0001) leucosapphire substrates coated by ultrathin gold layers

The real structure of ZnO films formed by magnetron sputtering on (0001) leucosapphire substrates coated by an ultrathin (less than 0.7 nm) Au buffer layer has been studied by high-resolution microscopy. It is shown that modification of the leucosapphire substrate surface by depositing ultrathin Au layers does not lead to the formation of Au clusters at the film–substrate interface but significantly improves the structural quality of ZnO epitaxial films. It is demonstrated that the simplicity and scalability of the technique used to modify the substrate surface in combination with a high (above 2 nm/s) film growth rate under magnetron sputtering make it possible to obtain high-quality (0001) ZnO epitaxial films with an area of 5–6 cm².     

Preparation and Characterization of MBE-grown Si/CaF2 Heterostructures

Growth and fabrication of silicon-on-insulator structures, based on heteroepitaxial growth of insulating films on Si, is an area of research that has rapidly developed in recent years. Thin CaF₂ films and Si/CaF₂ multilayers were prepared on {111}-oriented Si substrates by molecular beam epitaxy (MBE) and were investigated by RHEED and RBS. For epitaxial growth the Si substrates were cleaned using the ultraviolet/ozone surface cleaning method which is an effective tool to remove contaminants from the surface by low-temperature in-vacuo preheating. The growth of CaF₂ on such Si{111} substrates provides epitaxial layers with a high structural perfection. When this layer system, however, is used as a substrate for epitaxial Si growth the Si layers show always twin formation. Si layers without twins could be obtained only after deposition of thin amorphous Si buffer layers at room temperature, immediately followed by Si growth at 700 °C.     

A new graphite boat construction for the LPE growth of thin GaAs layers with a new technique

The characteristics of planar devices made of thin epitaxial GaAs layers on semiinsulating substrates, such as Gunn efect devices and MeSFETs, sensitively depend on the quality of the interface between the epitaxial layer and the substrate. The origin of an n-type, low resistivity interface layer between the epitaxial layer and the semiinsulating substrate is the semiinsulating substrate itself. The measured changes in the substrate-surface layer characteristics occur during the pregrowth heat treatment of the substrate in purified hydrogen. One solution of the problem could be shortening of the pregrowth heat treatment, but a low background doping concentration and a layer surface without any morphological defects only can be obtained after a relatively long pregrowth heat treatment of the melt. In this paper the technique of pregrowth melt preparation by heat treatment of the melt and the melt-back of the substrate prior to the growth is described. A new turnable sliding boat is presented which allows the use of as many melts as necessary for the required device (multilayer structures). Results (change of the electron concentration at the interface epitaxial layer-semiinsulating substrate, trap concentration, Hall mobility) and device characteristics (Gunn device under pulse and dc conditions and MeSFET) obtained with the improved technology are presented.     

Hexagonal AlN films grown on nominal and off-axis Si(0 0 1) substrates

Nucleation and growth of wurtzite AlN layers on nominal and off-axis Si(0 0 1) substrates by plasma-assisted molecular beam epitaxy is reported. The nucleation and the growth dynamics have been studied in situ by reflection high-energy electron diffraction. For the films grown on the nominal Si(0 0 1) surface, cross-sectional transmission electron microscopy and X-ray diffraction investigations revealed a two-domain film structure (AlN¹ and AlN²) with an epitaxial orientation relationship of [0 0 0 1]_AlN || [0 0 1]_Si and AlN¹ || AlN² || [1 1 0]_Si. The epitaxial growth of single crystalline wurtzite AlN thin films has been achieved on off-axis Si(0 0 1) substrates with an epitaxial orientation relationship of [0 0 0 1]_AlN parallel to the surface normal and 0 1 1 0_AlN || [1 1 0]_Si.     

The growth of Pd thin films on a 6H-SiC(0 0 0 1) substrate

Pd thin films, grown on Si-rich 6H-SiC(0 0 0 1) substrates, were studied by atomic force microscopy, electron diffraction and high-resolution transmission electron microscopy. It is concluded that the growth is successful only when all the growth process takes place at room temperature. Under these conditions a very good epitaxial growth of Pd is achieved, despite the large misfit (about 8.6%) between Pd and the substrate and the existence of a semi-amorphous layer between the thin film and the substrate. A large number of twins appear in these films.     

衬底温度对碲化镉薄膜结构及光学性能的影响

碲化镉(CdTe)因具有良好的光电性能和吸收性能经常被作为太阳电池的吸收层材料.以纯度为99.99;的CdTe陶瓷靶为靶材在玻璃衬底上采用射频磁控溅射的方法制备了一系列的CdTe薄膜,研究了衬底温度对样品薄膜的厚度、结构和光学性能的影响.结果表明:随着衬底温度的增加薄膜的厚度在逐渐地减少;制备的薄膜都是立方闪锌矿结构且具有高度的(111)面择优取向;薄膜对可见光有较好的吸收性能,随衬底温度的增加而减小.     

Abscheidung dünner Siliziumschichten durch Zersetzung eines Siliziumtetrahlorid-Wasserstoff-Gemisches in einer Hochfrequenz-Glimmentladung

The paper describes a technique for depositing thin films of silicon on several substrate materials by decomposition of a SiCl₄–H₂ mixture in a h.f. discharge. Depending on the growth conditions and on the substrates used the formed silicon layers are amorphous, polycrystalline or well defined monocrystalline. Vapour etching of differently orientated monocrystalline silicon substrates in the apparatus yields crystal surfaces which can be used as base for consecutive epitaxial growth.     

Growth and optical property characterization of textured barium titanate thin films for photonic applications

We have investigated the growth of barium titanate thin films on bulk crystalline and amorphous substrates utilizing biaxially oriented template layers. Ion beam-assisted deposition was used to grow thin, biaxially textured, magnesium oxide template layers on amorphous and silicon substrates. Growth of highly oriented barium titanate films on these template layers was achieved by molecular beam epitaxy using a layer-by-layer growth process. Barium titanate thin films were grown in molecular oxygen and in the presence of oxygen radicals produced by a 300 W radio frequency plasma. We used X-ray and in situ reflection high-energy electron diffraction (RHEED) to analyze the structural properties and show the predominantly c-oriented grains in the films. Variable angle spectroscopic ellipsometry was used to analyze and compare the optical properties of the thin films grown with and without oxygen plasma. We have shown that optical quality barium titanate thin films, which show bulk crystal-like properties, can be grown on any substrate through the use of biaxially oriented magnesium oxide template layers.