Yu.A. Vodakov

On mechanisms of sublimation growth of AlN bulk crystals

A novel model of bulk AlN crystal growth by the sublimation technique is developed. The model takes into account both di!usive and convective transport of gaseous Al and N 2 , and the kinetic limitation of nitrogen adsorption/desorption on AlN surfaces. The maximum growth rate is found to be controlled by joint e!ect of enhancement of the convective species transport in a nearly stoichiometric vapor phase and of the suppression of nitrogen incorporation into the crystal due to low N 2 sticking probability. The interplay of these e!ects provides nonmonotonic dependence of the growth rate on pressure. The theoretical predictions agree well with experimental data reported in literature and obtained in this work. ( 2000 Published by Elsevier Science B.V. All rights reserved.

Use of Ta‐Container for Sublimation Growth and Doping of SiC Bulk Crystals and Epitaxial Layers

Analysis of specific features of sublimation growth of bulk SiC crystals in presence of Ta is performed. Control of doping and formation of different SiC polytypes is discussed. Description of mechanisms responsible for generation of micropipes during sublimation growth of bulk crystals is given. It is shown that use of Ta is promising for growth of bulk SiC crystals.

Analysis of sublimation growth of bulk SiC crystals in tantalum container

Abstract Sublimation growth of SiC bulk crystals in tantalum container is studied both experimentally and theoretically. The model of heterogeneous processes occurred on the side wall of the tantalum container proposed recently in Ramm et al. (Mat. Sci. Eng. B 61–62 (1999) 107) is extended to take into account the process of carbon gettering by the container side wall. We formulate a quasi-steady approach for modeling of the bulk crystal growth. Using this concept we predict evolution of the crystal shape and study processes which govern SiC bulk crystal growth. We apply anisotropic thermal elastic analysis to predict stress distribution in the growing crystal. For the first time a model of dislocation formation is applied for SiC bulk growth to compute dislocation density field in highly stressed areas of the growing crystal.

High rate GaN epitaxial growth by sublimation sandwich method

Abstract Thick GaN epitaxial layers were grown by the sublimation “sandwich method” (SSM) on SiC substrates at temperatures from 1100°C to 1250°C in ammonia flow. Metallic Ga or GaN powder was used as the vapor source. The possibility of growing of monocrystalline GaN layers with growth rates as high as 1 mm/h was demonstrated. The dependence of the growth kinetics on temperature, source to substrate distance and input ammonia flow rate was studied. Various characterization techniques show the high quality of the GaN layers.

Sublimation Growth of AlN in Vacuum and in a Gas Atmosphere

The growth of AlN crystals by sublimation technique is investigated. Two mechanisms of Al and N2 transport from the source to the seed are distinguished — occurring predominantly via diffusion or via drift of the reactive species. Drift transport provides considerably higher growth rates compared to diffusive transport. The interplay of these mechanisms depends on temperature and gas pressure in the growth system. A theoretical model of AlN sublimation growth is developed allowing one to estimate the growth rate as a function of gas pressure and temperature. The theoretical predictions agree well with experimental observations obtained while growing AlN in the nitrogen atmosphere and in vacuum.

Growth of silicon carbide by sublimation sandwich method in the atmosphere of inert gas

Silicon carbide growth by sublimation sandwich method in the atmosphere of an inert gas is studied both experimentally and theoretically. An analytical description of diffusion transport of gaseous reactive species, coupled with quasi-equilibrium heterogeneous reactions at the source-wafer and substrate surfaces is derived. The species transport inside the sandwich cell is shown to be essentially determined by conditions in the ambience. The growth rate is studied as a function of process parameters (substrate temperature, temperature difference between the source-wafer and the substrate, and others). The developed approach is extended to the transient from the diffusion to the collisionless regime of the species transport. The theoretical results are in good agreement with the experimental data obtained.

Growth of silicon carbide bulk crystals by the sublimation sandwich method

Abstract Sublimation sandwich method used earlier to obtain SiC epilayers is applied for growth of SiC bulk crystals. The possibility to obtain the SiC crystals of different polytypes is demonstrated. Mechanisms of generation of micropipes during bulk growth of SiC are discussed.

Optimization of sublimation growth of SiC bulk crystals using modeling

Analysis of factors determining growth rate and shape of the crystallization front during sublimation growth of bulk SiC crystals is presented. For this purpose, mass transport of species in the graphite crucible coupled with global heat transfer in a sublimation growth system is studied. Specific features of the growth process in a tantalum container are discussed.

Analysis of silicon carbide growth by sublimation sandwich method

Abstract Basic mechanisms of growth of silicon carbide crystals using the sublimation sandwich method with reactive SiC C or SiC Si environment are studied both theoretically and experimentally. Dependence of the growth rate on the process parameters (substrate temperature, temperature difference between the source and the substrate, and temperature of the environment) is calculated using an advanced thermodynamic model. The effect of the environment on 6H SiC growth is studied in detail. The theoretical results are compared to the experimental data.

Transport phenomena in sublimation growth of SiC bulk crystals

Abstract Sublimation growth of SiC bulk crystals in the atmosphere of concentrated multi-component vapor is studied using a specially developed model of transport processes coupled with heterogeneous reactions at the source and the seed surfaces. The convective and multi-component diffusion mechanisms of the gas phase transport, dependence of the pressure level inside the growth chamber on the growth conditions, and kinetic jumps of the species partial pressures at the Knudsen layers on the reactive surfaces are taken into account in the model. The latter effect is described by introduction of novel boundary conditions representing extension of the Hertz–Knudsen relationship for the case of multi-component vapor. The results of calculations are shown to be in a good agreement with the available experimental data.