Deposition of bulk GaN from solution in gallium under high N2 pressure on silicon carbide and sapphire substrates

Results of high-pressure directional growth of GaN on foreign substrates: SiC, sapphire and GaN/sapphire MOCVD templates are presented. The role of nitrogen pressure and supersaturation in the growth process is discussed. The conditions for stable growth of the nitride are determined. The results of the crystallization process are compared with those obtained for directional growth on pressure grown GaN crystals.     

Anwendungsmöglichkeiten der Röntgentopographie zur Bestimmung der Oberflächengüte und der Realstruktur von Granateinkristallen

Single crystals of garnets of the rare earth are interesting in the development of bubble memories. Therefore it is necessary to controll the surface quality of the substrates and epitaxial layers during the different steps of preparation. X-ray topographic methods for testing the surfaces will be compared with the etching technique. Loop-configurations at inclusions are described and the mechanism for their formation will be discussed.     

Extrinsic doping of CdxHg1−xTe— A review

Extrinsic doping by elements which are stable to subsequent processing will become increasingly important in future infra-red device structures based on Cd_xHg_1−xTe. This paper reviews the incorporation and activation of dopants in the most widely used bulk and epitaxial growth methods. Stoichiometry at the growth temperature is shown to be the critical factor affecting dopant activation. Various factors, including stoichiometry, can affect the as-grown electrical properties and the importance of determining the type of conduction in the as-grown state, if successful extrinsic doping is to be accomplished, is stressed. Data on dopant segregation behaviour, in growth from liquids, acceptor ionization energies and carrier lifetimes are also presented and their importance is discussed.     

Study of growth and doping of semiconductor films by the method of computer simulation

The possibility of Computer Simulation Monte-Carlo Method for the study of growth and doping regularities of semiconductor films with diamond type lattice and for control of their parameters is considered. The events probabilities of isolation attachment and diffusion displacements of atoms on the growing surface of the basic material and doping impurities are compared. The periodic regional conditions on the boundary of the considered area are presented. It is shown the limitations of the computer simulation methods because of growth processes knowing level and computer possibility. The modeling calculations are made for growth and doping of one-component material films and for growth of two-component compounds. It can be noticed the connection between supersaturation, deposition temperature, time growth rate, surface film roughness (impurity atoms), capture coefficient, doping level, critical thickness of continuous films, defects density. Computer experimental results are compared with experimental data on growth and doping of Si, Ge, GaAs film with the various orientations from vapour or molecular beams in vacuum. The ways of further development of computer simulation method are discussed.     

Vapour phase epitaxy of II–VI compounds: A review

This paper is mainly concerned with a critical review of the present situation in the field of vapour phase epitaxy of II–VI compounds. LPE-methods have been less successful. Single-crystal films have been grown by vacuum deposition, sublimation, chemical transport and chemical vapour deposition (including metalorganic-hydride processes). Remarkable results h have been obtained with the close-spaced technique and the chemical vapour deposition methods. The following topics from the point of view of the most suitable operating conditions for epitaxy will be discussed: preparation of substrates and source materials, chemical equilibria and material transport, supersaturation in the growth zone and growth temperature. The compounds ZnS, ZnSe, ZnTe exhibit systematic connections for the material transport, orientation dependence of growth rates and the crystal structures. Considerable interest is shown in the epitaxy of II–VI compounds, because of interesting properties with regard to opto-electronic applications, as in electro-optic information storage devices, light emitting diodes and electroluminescent displays.     

硅基片上异质外延SiC的机理研究

本文利用低压高温MOCVD系统,成功地在Si(111)基片上外延出了具有高质量的SiC薄膜,并对其反应机理做了一些初步的研究.大部分观点认为,SiC/Si的异质外延,其最初的状态应该为Si衬底中Si的扩散.但是,本文通过在不同流量比的条件下,SiC薄膜在Si基片以及Al2O3基片上外延的比较,发现在SiC/Si的异质外延过程中起重大作用的并非Si衬底中Si的扩散,而是很大程度上作用于C向Si衬底的扩散.同时,还发现反应速率的快慢受SiH4流量所限制.当SiH4流量增加时,反应速率会明显加快,但是结晶质量会相对变差.     

The Problem of a Near Surface Quasi-Gas Transition Layer in MBE

A survey of experimental data related to the problem of a near surface quasi-gas (NSQG) transition layer in molecular beam epitaxy (MBE) has been presented and the arguments suggesting the existence of such a transition layer have been discussed. Subsequently, the application of the NSQG layer concept to morphological stability analyzis of MBE and to the phase-locked MBE has been discussed. The experimental data presented suggest that in growing extremely flat layer structures, e.g., superlattice structures, a growth mode for MBE should be chosen in which the NSQG layer is maximally thin, however, when growing planar epilayers over patterned substrates such MBE growth mode should be chosen in which the creation of a thick (on an atomic scale) NSQG layer would be possible.     

The growth kinetics of (SmY)3(FeGa)5O12 epitaxial layers in the 920–980°C range

The growth kinetics of (SmY)₃(FeGa)₅O₁₂ garnets obtained by liquid phase epitaxy on Gd₃Ga₅O₁₂ substrates are discussed in the 920 to 980°C. range. The experiments have been carried out with the substrates in a horizontal plane and with unidirectional rotation ranging from 30 to 300 rotations per minute (rpm). A sharp increase in the growth velocity at temperatures higher than 960°C is interpreted on the basis of a diffusion-reaction theory. It is found that the diffusion constant increases steeper at higher temperatures and that the linear law of the growth rate as a function of the square root of the rotation rate holds to much higher rotation rates at these temperatures. The influence of the surface incorporation is too small to be detectable. The results are compared with published data concerning other compositions.     

SiC单晶片的取向研磨

优质晶体生长常常需要籽晶或衬底偏离常规结晶取向.为便于按任意偏向角度研磨晶片,本实验室设计并应用了晶片取向研磨夹具及相应的研磨工艺.本文介绍了该夹具和工艺的工作原理、技术要点以及对技术指标的鉴定情况.测试结果表明,研磨取向误差范围可控制在5;之内,研磨片厚度偏差小于5 μm、粗糙度Ra=0.12 μm.     

AgGaSe2 on {100} and {110} GaAs—Special Features of Epitaxial Growth

AgGaSe₂ thin epitaxial layers onto {100} and {110} oriented GaAs substrates were prepared by flash evaporation technique and investigated by the RHEED method (reflection high energy electron diffraction). Special epitaxial relationships were found and the results will be discussed.     

Silicon nanowire growth by electron beam evaporation: Kinetic and energetic contributions to the growth morphology

The vertical and epitaxial growth of long (up to a few microns) silicon nanowires on Si(1 1 1) substrates by electron beam evaporation (EBE) (10⁻⁶–10⁻⁷ mbar) is demonstrated at temperatures between 600 and 700 °C following the vapour–liquid–solid (VLS) growth mechanism from gold nanoparticles. The silicon atoms are provided by evaporating silicon at varying evaporation currents (I_E) between 35 and 80 mA, which results in growth rates between 1 and 100 nm/min. The growth peculiarities in the interaction triangle, evaporation current (I_E), growth temperature (T_S) and gold layer thickness (d_Au) will be reported. Kinetic and energetic contributions to the morphology of silicon nanowires will be discussed.     

Characterization of the silicon-sapphire interface

Two examples of nucleation of silicon on sapphire (SOS) will be discussed as observed during (1) a standard deposition performed on an industrial vertical reactor and (2) a deposition performed in an horizontal reactor working at reduced pressure. The first stages of nucleation have been observed by Transmission Electron Microscopy (TEM). The last stages of nucleation have been studied by Scanning Electron Microscopy (SEM). On thick deposits Secondary Ion Mass Spectroscopy (SIMS) which gives aluminum profiles has been performed. Correlation on nucleation results with electrical measurements on integrated devices will be presented.     

Suppression of phase separation in InGaN layers grown on lattice-matched ZnO substrates

Sapphire and SiC are typical substrates used for GaN growth. However, they are non-native substrates and result in highly defective materials. The use of ZnO substrates can result in perfect lattice-matched conditions for 22% indium InGaN layers, which have been found to suppress phase separation compared to the same growths on sapphire. InGaN layers were grown on standard (0 0 0 2) GaN template/sapphire and (0 0 0 1) ZnO substrates by metalorganic chemical vapor deposition. These two substrates exhibited two distinct states of strain relaxation, which have direct effects on phase separation. InGaN with 32% indium exhibited phase separation when grown on sapphire. Sapphire samples were compared with corresponding growths on ZnO, which showed no evidence of phase separation with indium content as high as 43%. Additional studies in Si-doping of InGaN films also strongly induced phase separation in the films on sapphire compared with those on ZnO. High-resolution transmission electron microscopy results showed perfectly matched crystals at the GaN buffer/ZnO interface. This implied that InGaN with high indium content may stay completely strained on a thin GaN buffer. This method of lattice matching InGaN on ZnO offers a new approach to grow efficient emitters.     

Comparison of photocurrent spectra measured by FTPS and CPM for amorphous silicon layers and solar cells

Fourier Transform Photocurrent Spectroscopy (FTPS) has been recently introduced as a fast and highly sensitive method for the evaluation of the optical absorption coefficient of photoconductive thin films such as microcrystalline silicon layers. This contribution represents the first study of FTPS utilization for amorphous silicon layers and cells. FTPS spectra are compared with results of Constant Photocurrent Method (CPM) and Dual Beam Photoconductivity (DBP) measured at different chopping frequencies. We will concentrate to highlight the appropriate measuring conditions and evaluation procedures for correct data interpretation. Moreover, we will present our novel approach for the interference free determination of absorption coefficients of thin films grown on transparent substrates, which is mainly important for very thin layers where broad interference fringes do not allow correct evaluation of parameters such as a slope of the Urbach tail and the defect density.     

Liquid Phase Epitaxy (LPE) of YB2Cu3O7-δ High Tc Superconductors

YBa₂Cu₃O_7-δ films were grown by liquid phase epitaxy in Y-ZrO₂ crucibles on (110)NdGaO₃ substrates. A change in the preferred crystallographic growth direction was observed reproducibly. The growth mode changes from pure c-axis oriented over mixed c/a-axis oriented films to pure a-axis oriented films with increasing undercooling. X-ray diffraction measurements and atomic force microscopy investigations with c-axis oriented as well as a-axis oriented films are presented. It will be shown that atomically smooth steps with 0.2-0.8 μM width can be achieved by LPE, which are free from melt remnants. Furthermore the values for the enthalpy of dissolution from literature, which are varying in a wide range, will be combined and a new value will be calculated in terms of a multi particle model.     

Controlled lattice constant mismatch by compositional changes in liquid phase epitaxially grown single crystal films of rare earth yttrium iron gallium garnets on gadolinium gallium garnet substrates

Liquid phase epitaxy (LPE) by dipping substrates into supercooled fluxed solution provides a convenient way of changing the melt and film composition. The apparatus, method and composition of the melts that we use will be described in detail. The composition of the layer is essentially Y₃GaFe₄O₁₂, which has a smaller lattice constant than the Czochralski-grown gadolinium gallium garnet substrate. By substitutions such as gadolinium, samarium or lanthanum for yttrium the lattice constant mismatch can be controlled. The effect of these substitutions on film properties such as cracks, stresses and magnetic domain pattern as well as the interaction of substrate defects such as dislocations with the epitaxially-grown film are discussed.     

多孔镁基板上纳米厚度氢氧化镁叠片的水热合成研究

通过水热法在烧结的多孔镁基板上制备了纳米厚度的氢氧化镁(Mg(OH)2)叠片.分别用SEM及XRD表征了水热合成过程中基板的形貌和物相变化.结果表明,将水热合成的反应时间控制在20 ～ 40 min之内,可以制备出具有100 nm左右厚度的、不同紧密程度的Mg(OH)2叠片.水热合成的反应时间超过40 min,Mg(OH)2叠片将会逐渐从基板表面生长合并为块状晶体.同时,对水热反应过程中氢氧化镁晶体的形核和长大机理进行了探讨.     

Si–Ge–Sn alloys: From growth to applications

In this review article, we address key material parameters as well as the fabrication and application of crystalline GeSn binary and SiGeSn ternary alloys. Here, the transition from an indirect to a fundamental direct bandgap material will be discussed. The main emphasis, however, is put on the Si–Ge–Sn epitaxy. The low solid solubility of α-Sn in Ge and Si of below 1 at.% along with the large lattice mismatch between α-Sn (6.489 Å) and Ge (5.646 Å) or Si (5.431 Å) of about 15% and 20%, respectively, requires non-equilibrium growth processes. The most commonly used approaches, i.e. molecular beam epitaxy (MBE) and chemical vapor deposition (CVD), will be reviewed in terms of crucial process parameters, structural as well as optical quality and employed precursor combinations including Germanium hydrides, Silicon hydrides and a variety of Sn compounds like SnD₄, SnCl₄ or C₆H₅SnD₃. Special attention is devoted to the growth temperature window and growth rates being the most important growth parameters concerning the substitutional incorporation of Sn atoms into the Ge diamond lattice. Furthermore, the mainly CVD-driven epitaxy of high quality SiGeSn ternary alloys, allowing the decoupling of band engineering and lattice constant, is presented. Since achieving fundamental direct bandgap Sn-based materials strongly depends on the applied strain within the epilayers, ways to control and modify the strain are shown, especially the plastic strain relaxation of (Si)GeSn layers grown on Ge.Based on recently achieved improvements of the crystalline quality, novel low power and high mobility GeSn electronic and photonic devices have been developed and are reviewed in this paper. The use of GeSn as optically active gain or channel material with its lower and potentially direct bandgap compared to fundamentally indirect Ge (0.66 eV) and Si (1.12 eV) provides a viable solution to overcome the obstacles in both fields photonics and electronics. Moreover, the epitaxial growth of Sn-based semiconductors using CMOS compatible substrates on the road toward a monolithically integrated and efficient group IV light emitter is presented.     

Liquid phase epitaxial growth of Ga1−xAlxAs on channeled substrates

The growth mechanism of liquid phase epitaxial layers of Ga_1?xAl_xAs on preferentially etched GaAs substrates has been investigated. It has been found that enhanced diffusion of As atoms due to a local concentration gradient, which is set up by non-uniform growth at channels, plays a critical role in determining the growth morphology. The relation between growth morphology and growth conditions is discussed by using a simple growth model.