Analysis of the low gravity tolerance of Bridgman-Stockbarger crystal growth. II, Transient and periodic accelerations

The effects of single and multicomponent oscillatory residual accelerations on dopant distribution in gallium-doped germanium crystals grown by the Bridgman-Stockbarger technique is investigated numerically. The multicomponent disturbances include three-component accelerations and complex acceleration profiles synthesized from Fourier analyses of acceleration data obtained on the Spacelab-3 (SL-3) mission. We find that the largest compositional nonuniformities occur for disturbances with amplitudes above 10-6 g and frequencies below 10-2 Hz. At higher frequencies, larger acceleration amplitudes are required to obtain significant nonuniformities. These nonuniformities are barely detectable at early times, reach a maximum after the velocity transient and subsequently decrease over the characteristic concentration diffusion time. The effect of several “g-jitter” profiles synthesized from SL-3 measurements with frequencies between 10-1-10 Hz is examined. The system is found to exhibit marginal sensitivity to only one of these acceleration profiles.