Influence of crystal—melt interface shape on self-seeding and single crystalline quality

The growth of Sb-based crystals (InSb, GaSb etc) was undertaken using resistive heater furnace by vertical directional solidification (VDS) technique. Crystal—melt interface shape during the growth was shown to convert from concave to convex along the crystal axis of the ingots. Many antimonide (Sb) crystals of 8 mm to 18 mm diameter were grown by optimized growth parameters. The forced convection and absence of conducting support to ampoule showed improvement in crystal quality of as grown ingots. Crystals showed preferred orientation and self-seeding. Results on interface shape and crystallinity of ingots were found to be in good agreement with the experiments.     

φ300mm的大直径直拉单晶硅勾形磁场下生长的数值模拟

直径300mm硅片的生产技术是当今硅材料生产研究的重要方向之一,而晶体生长 界面的形状、温度分布、晶体中氧的浓度和均匀性等对熔体流动状态十分敏感,采用实验的方 法来测量熔体的流动、温度场分布是很困难的,因此很难通过实验的方法获得熔体的流动是如 何影响晶体生长的质量的,而数值模拟能提供熔体流动、温度分布等详细内容,为单晶硅的生 长提供有利的指导.本文采用低雷诺数的K-ε紊流模型,对直径300mm的大直径单晶硅生 长进行了数值模拟,通过熔体在有、无勾形磁场作用时的流场、温度场的分析,阐明了勾形磁 场影响熔体流动的机理.     

MOVING BOUNDARY COMPUTATION OF THE FLOAT-ZONE PROCESS

A computational capability has been developed to predict the free surface shape, heat transfer and melt–crystal interface shapes in float-zone processing. A moving boundary, second order, finite volume, incompressible Navier–Stokes solver has been developed for the fluid flow and heat transfer calculations. The salient features of the approach include solving the dynamic form of the Young–Laplace equation for the free surface shape, dynamic remeshing to fit the free boundary, a flexible, multi–block, grid generation procedure and the enthalpy method to capture the melt–crystal and the melt–feed interfaces without the need for explicit interface tracking. Important convective heat transfer modes; natural convection and thermocapillary convection have been computed. It is shown that, whereas the overall heat transfer is not substantially affected by convection, the melt–crystal interface shape acquires significant distortion due to the redistribution of the temperature field by the thermocapillary and buoyancy-induced convective mechanisms. It is also demonstrated that the interaction of natural and thermocapillary convection can reduce the melt–crystal interface distortion if they act in opposing directions. It is found that the meniscus deformation can cause the height of the zone to increase but the qualitative nature of the melt–solid interface shapes are not significantly affected. Results are compared with literature to validate the predictive capability developed in this work. © 1997 by John Wiley & Sons, Ltd.     

Viscosity of Molten GaSb and InSb

Viscosities of molten GaSb and InSb as III–V compound semiconductors were measured using an oscillating viscometer to study the thermophysical properties of semiconductor melts. A specially designed quartz crucible was used to prevent the evaporation of Sb from the melts. The measurements were performed in the temperature ranges from the melting point to about 1490 K for GaSb and from supercooled temperatures to about 1340 K for InSb. The viscosities obtained for both GaSb and InSb showed good Arrhenius linearity despite their wide temperature ranges. The activation energies of GaSb and InSb were almost the same, although the absolute viscosity of GaSb was slightly higher than that of InSb. It was concluded that most semiconductors including Si and Ge show Arrhenius behavior and have a low viscosity. The reason for the low viscosity is considered to be related to their melt structure, which may be similar to that of molten metals with low melting points.     

垂直布里奇曼法CdZnTe晶体生长过程的数值分析

模拟计算了半导体材料CdZnTe布里奇曼法单晶体生长过程，分析了熔体的过热温度、坩埚侧面强化换热以及坩埚加速旋转(ACRT)等因素对结晶界面的形态和晶体组分偏析的影响。结果表明：当熔体的过热温度减小时，熔体中自然对流的强度显著降低，固液界面的凹陷深度有所增加，晶体的轴向等浓度区显著加长，而晶体组分的径向偏析明显增大，坩埚的侧面强化换热增加了自然对流强度，也增大了固液界面的凹陷，但是对溶质成分的偏析影响较小，坩埚加速旋转引起的强迫对流强度远大于自然对流，显著增大了固液界面的凹陷，使熔体中的溶质分布成为均一的浓度场，显著减小了晶体组分的径向偏析，增加了晶体组分的轴向偏析。     

Liquid phase epitaxy of (Sn<Subscript>2</Subscript>)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(InSb)<Subscript>x</Subscript> solid solution layers

Epitaxial layers of (Sn₂)_1?x(InSb)_x solid solutions were grown from an indium-based solution melt confined between two horizontal GaAs substrates in a temperature interval from 325 to 200°C. Scanning microprobe and X-ray diffraction investigations of the GaAs-(Sn₂)_1?x(InSb)_x heterostructures showed that crystallographic perfection of the epitaxial layers depends on the epitaxial growth conditions.     

A numerical investigation of dopant segregation by modified vertical gradient freezing with moderate magnetic and weak electric fields

The paper numerically investigates melt growth of doped gallium-antimonide (GaSb) semiconductor crystals by the vertical gradient freeze (VGF) method utilizing a submerged heater. Electromagnetic (EM) stirring can be induced in the gallium-antimonide melt just above the crystal growth interface by applying a small radial electric current in the melt together with an axial magnetic field. The transport of any dopant by the stirring can promote better compositional homogeneity. This investigation presents a numerical model for the unsteady transport of a dopant during the VGF process by submerged heater growth with a moderate axial magnetic field and a weak electric field. Numerical predictions of the dopant distributions in the crystal and in the melt at several different stages during growth are presented.     

Transmission electron microscopy study of the initial growth stage of GaSb grown on Si (001) substrate by molecular beam epitaxy method

The microstructural properties at the initial growth stage of the GaSb heteroepitaxial growth on a silicon (Si) substrate were investigated using transmission electron microscopy. Well-separated and tall GaSb islands were observed when GaSb was directly grown on a Si substrate (sample A). On the other hand, GaSb was grown to the coalesced and flat islands when a low-temperature AlSb buffer (sample B) was introduced. The different morphologies of the GaSb islands were related to the microstructural properties of the interface between the GaSb and the Si substrate. The GaSb/Si interface was rough, and disordered atomic arrangements were observed at the interface in sample A. On the other hand, the GaSb/Si interface was flat, and well-ordered atomic arrangements appeared at the interface in sample B. Entirely different mechanisms for the relaxation of a misfit strain were demonstrated from a microstructural viewpoint.     

Measurement of the diffusion coefficient of rare earth species in PbO-B2O3 flux used for liquid phase epitaxial growth of magnetic garnet films

The solute diffusion coefficient in a PbO-B₂O₃ flux system used for the growth of magnetic garnet films has been measured by two different techniques and found to be (5±1.5)×10^?7 cm²/sec in the growth temperature range of 840°C–887°C. In the first technique, for a nearly stagnant melt, the film thickness is proportional to the square root of the growth time after subtraction of the residual effects of convection. In the second technique the melt is stirred by rotating the substrate. The growth rate is constant after an initial transient, and is proportional to the square root of the rotation rate.     

Chemical interaction of InAs,InSb, GaAs,and GaSb crystal surfaces with (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript>–HBr–citric acid etching solutions

We have studied the chemical dissolution of InAs, InSb, GaAs, and GaSb crystals in (NH₄)₂Cr₂O₇–HBr–C₆H₈O₇ solutions. The dissolution rate of the crystals has been measured as a function of etchant composition, and the kinetics of the chemical interaction of the semiconductors with solutions have been investigated in detail. The dissolution rate has been shown to be diffusion-limited. Citric acid helps to reduce the etch rate and improves the polishing performance of the etching solutions.     

砷化镓单晶的等效微重力生长

论述了砷化镓晶体的等效微重力生长的原理和所采用的方法,并讨论了主要结果。     

Effects of convective fluid motion upon oxide crystal growth in high temperature solution

For understanding of the influence of convective flow on crystal growth, space high temperature in situ observation instrument (SHITISOI) is dedicated to visualize and record the whole growth process of oxide crystals in high temperature up to 1,000°C. Model experiments using transparent liquids such as KNbO₃ and a mixture of Li₂B₄O₇+KNbO₃ were chosen to investigate effects on ground and in space. On the earth, an investigation of growth kinetics of KNbO₃ crystal related to two different states of convection: diffusive-advective flow and diffusive-convective flow, has been performed. The per unit length of a step e is calculated from the experimental data for two different states of convection. Analyses of these data show the effect of buoyancy convection is to enhance the sharpness of the interface. The growth of KNbO₃ crystals from solution of KNbO₃+Li₂B₄O₇ was investigated in space. The streamlines of the steady thermocapillary convection in Li₂B₄O₇ solvent was observed. Due to thermocapillary convection, KNbO₃ crystal grains grew and filled the whole solution homogeneously. Earth-based quenching experiments are designed in order to study polyhedral instability of KNbO₃ crystal, which is controlled by diffusion mechanism limitation. In all cases, when the crystal was nucleated near air/solution surface, it lost its polyhedral stability and varied from polyhedrons to dendrites. The thickness of diffusion mechanism limitation layer is about 60 μm.     

微重力条件下熔体中对流过程的数值模拟

微重力条件下生长优质晶体遇到的最大问题是要控制晶体生长的条件，抑制由于重大的减弱而引起的熔体中的热毛细时流。但是，用实验来解决这些问题费用高，周期也长，而且有时完全用实验来模拟也是很困难的。用数值计算方法来模拟微重力条件下熔体中的对流过程是空间晶体生长研究的一个重要的方向，计算结果对控制空间生长晶体和抑制熔体中的对流有指导意义。对微重力条件下熔体中对流发生、发展的过程进行了数值研究。以有限差分法研究了沿上表面为自由表面的水平区域不同边界条件下的熔体中的对流过程。     

Effects of convective fluid motion upon oxide crystal growth in high temperature solution

For understanding of the influence of convective flow on crystal growth, space high temperature in situ observation instrument (SHITISOI) is dedicated to visualize and record the whole growth process of oxide crystals in high temperature up to 1,000°C. Model experiments using transparent liquids such as KNbO₃ and a mixture of Li₂B₄O₇+KNbO₃ were chosen to investigate effects on ground and in space. On the earth, an investigation of growth kinetics of KNbO₃ crystal related to two different states of convection: diffusive-advective flow and diffusive-convective flow, has been performed. The per unit length of a step e is calculated from the experimental data for two different states of convection. Analyses of these data show the effect of buoyancy convection is to enhance the sharpness of the interface. The growth of KNbO₃ crystals from solution of KNbO₃+Li₂B₄O₇ was investigated in space. The streamlines of the steady thermocapillary convection in Li₂B₄O₇ solvent was observed. Due to thermocapillary convection, KNbO₃ crystal grains grew and filled the whole solution homogeneously. Earth-based quenching experiments are designed in order to study polyhedral instability of KNbO₃ crystal, which is controlled by diffusion mechanism limitation. In all cases, when the crystal was nucleated near air/solution surface, it lost its polyhedral stability and varied from polyhedrons to dendrites. The thickness of diffusion mechanism limitation layer is about 60 μm.     

Crystal structure control in Au-free self-seeded InSb wire growth

In this work we demonstrate experimentally the dependence of InSb crystal structure on the ratio of Sb to In atoms at the growth front. Epitaxial InSb wires are grown by a self-seeded particle assisted growth technique on several different III-V substrates. Detailed investigations of growth parameters and post-growth energy dispersive x-ray spectroscopy indicate that the seed particles initially consist of In and incorporate up to 20?at.% Sb during growth. By applying this technique we demonstrate the formation of zinc-blende, 4H and wurtzite structure in the InSb wires (identified by transmission electron microscopy and synchrotron x-ray diffraction), and correlate this sequential change in crystal structure to the increasing Sb/In ratio at the particle-wire interface. The low ionicity of InSb and the large diameter of the wire structures studied in this work are entirely outside the parameters for which polytype formation is predicted by current models of particle seeded wire growth, suggesting that the V/III ratio at the interface determines crystal structure in a manner well beyond current understanding. These results therefore provide important insight into the relationship between the particle composition and the crystal structure, and demonstrate the potential to selectively tune the crystal structure in other III-V compound materials as well.     

Material dependence of electronic sputtering induced by MeV-energy heavy ions

Masses, yields and emission energies of secondary ions have been systematically measured for solid targets bombarded by Si ions over an energy range between 0.5 and 5 MeV for studying roles of the electronic collision in the formation process of secondary atomic ions. The targets used were insulators (Al₂O₃, SiO₂), semiconductors (Si, GaP, GaAs, GaSb and InSb) and a metal (Al). The obtained feature of the secondary ion emission depends characteristically on the target species. Singly and multiply charged positive ions are produced for Al, Si and P, respectively, from the Al, Al₂O₃, Si, SiO₂ and GaP targets. In the cases of GaAs, GaSb and InSb, however, the production rates of positive As and Sb ions are strongly depressed. The obtained emission energy distributions of atomic ions from the conductor and the semiconductors are very broad and have gradually decaying tails at the high-energy side in contradiction to those of singly charged atomic and cluster ions from the insulators. The most probable and mean energies of atomic ions are proportional to their electric charge irrespective of the target conductivity. Large cluster ions are produced from the SiO₂, Al₂O₃, GaSb and InSb targets. The yields of clusters from SiO₂, GaSb and InSb show power-law dependences on their sizes and the yield of clusters from Al₂O₃ decreases exponentially with increasing size. These results show that the clusters from SiO₂, GaSb and InSb are emitted directly from the surface. The clusters from Al₂O₃ may be indirectly produced by coagulation of molecules in a selvage region near the surface.     

Wetting in the ThO2/Me (Me?=?Ce, Al, U) systems: an example of the liquid phase properties role in reactive wetting

In this study, the wettability properties and chemical reactions in ThO₂ (~90?% dense)/Me (Me?=?Ce, Al, U) were measured. Sessile drop experiments were carried out at 1000, 1150, and 1250?°C for 60?min and the final apparent contact angles measured were 22°?±?2°, 45°?±?2°, and 135°?±?3°, respectively. Chemical reaction at the interface was detected only in the case of ThO₂/Al, where a thick (100–200?μm) C⁴ structure layer containing α-Al₂O₃ and Th-rich Al metallic phases were found. In this study, correlation between the thermodynamic properties of the binary Me–Th melts, chemical reaction at the interfaces, and spreading behavior was demonstrated. The Th–Al liquid solution has a negative departure from ideality and the chemical reaction at the ThO₂/Al interface was massive. The Th–U liquid solution displays a positive departure from ideality and the chemical reaction at the ThO₂/U interface was negligible. Th–Ce liquid solution displays a close to ideal behavior with a small positive departure from ideality, which promoted spreading without significant Th dissolution in the Ce melt and no detectable formation of new oxides at the interface. It is proposed that the mild chemical reaction in the ThO₂/Ce system is ideal for pressure-free infiltration processes. The dominance of the liquid solution properties concerning wettability behavior and chemical reaction at the interface was demonstrated using thermodynamic evaluation.     

Excellent compositional homogeneity in In0.3Ga0.7As crystals grown by the traveling liquiduszone (TLZ) method

The influence of convection in a melt on the compositional homogeneity of the TLZ-grown In_0.3Ga_0.7As crystals has been investigated by growing crystals with various dimensions on the ground. Excellent compositional homogeneity such as 0.3 plus or minus 0.01 in InAs mole fraction for a distance of 25 mm was obtained when the melt diameter was limited to 2 mm and convective flow in the melt was suppressed. On the other hand, when the crystal diameter was increased to 10 mm, both axial and radial compositional homogeneity was deteriorated due to convection in the melt. Comparing with the numerical simulation, convective flow velocity less than 1.4 mm/h may be sufficient for growing homogeneous crystals and it is not so difficult to suppress convective flow velocity below 1.4 mm/h for 10 mm diameter crystals in microgravity. Therefore, larger homogeneous In_0.3Ga_0.7As crystals are expected to be grown by the TLZ method on board the International Space Station.     

Dissolution kinetics of primary silicon in hypereutectic Al–Si melt

The dissolution process of primary silicon particles in Al–18%wt silicon alloy was studied both by a melt overheating experiment and by theoretical analysis. A dissolution model of primary silicon in the melt was established based on atomic diffusion and taking account to interface reaction and curvature of particles. The results show that the theoretical curve agrees with the experimental curve at an overheating temperature of 1100°C. However, there was some deviation at 700°C due to retained silicon clusters in the melt at lower temperature. Therefore, the model is in accord with experiment when not considering the influence of retained silicon clusters.