Affiliation:
1. Stony Brook University
Abstract
Cloudiness, bubble core defects, anomalous absorption, low-angle grain boundaries, and cracking are the main problems in the growth of high quality and large diameter (>7cm) Yb:S-FAP crystals utilizing the Czochralski method. The generation mechanism of these defects is highly related to transport phenomena in the growth system. In this paper, firstly, inductive, conductive and radiative heat transport phenomena are examined in the entire growth system. Then, an integrated modeling and experimental study is presented to determine an efficient means to eliminate or reduce crystal cracking during cooling. A process model has been developed to simulate the crystal cooling process. The effect of temperature distribution on thermal stress in the crystal during cooling is predicted by a simple but effective computational algorithm. With the relationship between the power change and crystal surrounding temperature change, the process model is further used to optimize power ramp-down profile to avoid cracking of the crystal during cooling-down process.