(298g) Effects of Several Heat Shield On the Crystallization Front of Sapphire Crystal Grown By Kyropoulos Method

In the growth of sapphire crystals, the critical density of dislocations determined by variations of the ratio of G/V affects on the quality of crystal structure. Where G is the axial temperature gradient and V is the velocity of crystallization front (CF). In general, it is not the initial temperature gradient is so important for structure control but rather the degree of its constancy maintaining during growth. However in Kyropoulos (KY) method the CF, has formed the inverse shape of cone, is gradually down to crucible bottom. Therefore it is more difficult to control its consistency during growth in KY method than other methods.

 In our experiments, we have studied the influences of heat shield (HS) on the formation of low angle block or grain boundaries (LAGB) and micro-bubbles. We have estimated the angle and velocity of convex of CF in several HS configurations. The shapes of CF are determined by the patterns of micro-bubbles generated by the power down-and-up test (PDU) in quick time. And the defects such as LAGB and micro-bubbles are inspected in the vertical slug which had been cut in center line of grown crystals by polarized microscope. The velocities are measured in PDU-tests by the evaluation data of vertical slugs and calculated by SK Forecast (developed by Alyuda.com) and our simulators.

 The defects free shape of CF is depended on the HS configurations with respect to time. It means that there exist an optimal tendency of CF in each HS. The LAGB is related to the acceleration of growth rate and the micro-bubble is related to the oscillation of growth rate that will be discussed in detail. The difference between our simulators and SK Forecast are come from the consideration of energy conservation and initial guessing value of angle and velocity of CF.