A Study on Radial and Axial Temperature Effects on the Growth of Bulk Single Crystal of SixGe1-x in Bridgman Setting
thesisposted on 22.05.2021, 12:20 by Mehdi Mohammadi Shemirani
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.