Thermal field simulation and heat zone optimization for the growth of 50-mm basal-plane-faceted sapphire ribbons
The global heat transfer during growth of 50-mm basal-plane-faced sapphire ribbons in a cylindrical heat zone has been numerically simulated for different heat shield configurations. The ribbon thermoelastic strains were computated to estimate the heat zone quality. It is shown that shield adjustment and redistribution of radiative heat fluxes inside the heat zone make it possible to essentially decrease the thermal field curvature in the ribbon around the crystallization front and, therefore, decrease the thermoelastic strains by a factor of 2 to 3 (to 20 MPa).