COMPARISON OF OARE ACCELEROMETER DATA WITH DOPANT DISTRIBUTION IN SE-DOPED GAAS CRYSTALS GROWN DURING USML-1

Experiments were conducted in the crystal growth furnace (CGF) during the first United States Microgravity Laboratory (USML-1), the STS-50 f light of the Space Shuttle Columbia, to determine the segregation beha vior of selenium in bulk GaAs in a microgravity environment. After the flight, the selenium-doped GaAs crystals were sectioned, polished, an d analyzed to determine the free carrier concentration as a function o f position. One of the two crystals initially exhibited an axial conce ntration profile indicative of diffusion controlled growth, but this p rofile then changed to that predicted for a complete mixing type growt h. An analytical model, proposed by Naumann [R.J. Naumann, J. Crystal Growth 142 (1994) 253], was utilized to predict the maximum allowable microgravity disturbances transverse to the growth direction during th e two different translation rates used for each of the experiments. Th e predicted allowable acceleration levels were 4.86 mu g for the 2.5 m u m/s furnace translation rate and 38.9 mu g for the 5.0 mu m/s rate. These predicted values were compared to the Orbital Acceleration Resea rch Experiment (OARE) accelerometer data recorded during the crystal g rowth periods for these experiments. Based on the analysis of the OARE acceleration data and utilizing the predictions from the analytical m odel, it is concluded that the change in segregation behavior was not caused by any acceleration events in the microgravity environment.