Abstract

This research explores simulation of the growth of large diameter single bulk crystals of silicon and germanium alloy from its melt utilizing Bridgman method. Producing homogeneous single bulk crystals requires a good understanding of the thermo-solutal behavior in the solvent region. This study also suggests certain fundamental scientific aspects of this alloy system which are not well considered to date, and which underlie both the homogeneity and obtaining relatively flat solid liquid interface of the SixGe1-x alloy. These aspects are the diffusion and transport of silicon and germanium in the molten alloy. Both three and two dimensional numerical simulations of thermo-solutal convection in solvent region were examined. The whole simulation scheme was applied to a cylindrical model representing the sample to investigate the aforementioned phenomena in the entire process. It was found that the application of axial magnetic field had no significant effect on the buoyancy driven convection in the solvent region. However, conducting the microgravity environment simulation has shown that the removal of the gravitational force on the solvent region would result in a homogeneous solidification. As an alternative, this study has found that both axial and radial temperature gradients play a role in the solidification process. Controlling this phenomenon, along with two other factors such as applied uniform temperature and reduced pulling rate, would help achieve a homogeneous single bulk crystal with more uniform silicon distribution in the solvent region, more specifically near the solid liquid interface and produce a flat shape interface which is most desired shape in industry.

Highlights

  • Crystal growth of multi-component alloys like SixGe1-x is an inherently complex process since it involves coupled and non-linear interactions of fluid flow, heat and mass transport, phase diagrams, phase changes, surface and interface phenomena, and other micro- and macro-level interactions

  • 2.1 Methods or Techniques There are many different methods and techniques which have been used for the crystal growth purposes, from early twentieth century, among which the four most practiced ones are; Czochralski technique (Cz), Bridgman method, Floating zone technique (FZ) and traveling solvent method (TSM) known as traveling heater method (THM)

  • The present results indicate that for each one of the three semiconductors ( GeGa, GaAsSe, SnBi) considered, the reduced longitudinal and radial segregation are practically insensitive to the pulse shape, rectangular or half-sinusoidal

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Summary

Introduction

Crystal growth of multi-component alloys like SixGe1-x is an inherently complex process since it involves coupled and non-linear interactions of fluid flow, heat and mass transport, phase diagrams, phase changes, surface and interface phenomena, and other micro- and macro-level interactions. The convective heat, momentum and mass transport processes in the melt result in significant uncertainties in the experimental measurement of physical parameters such as diffusion coefficients, and affect the evolution of the growth interface, crystal composition uniformity, impurity and inclusions, interface kinetics, surface curvature, etc. We present the results obtained with non-linear temperature profile (a polynomial of sixth-order) which experimentally obtained by Professor Labrie at Dalhousie University, and linear temperature profile when applied to the model in different conditions These are; terrestrial, microgravity and terrestrial with different applied axial magnetic field and under two temperature profile regimes, linear and non-linear, using Vertical Bridgman Method (VBM). Given the chemical composition of the solvent region, the pulling rate, and thermal gradient both axially and radially are playing a strong role in the process of crystal growth [20]

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