SYNCHROTRON CHARACTERIZATION OF Zn-ALLOYED CdTe COMPOUND SEMICONDUCTORS PROCESSED IN MICROGRAVITY ON STS 50 AND 73. D.J. Larson, Jr., M. Dudley, H. Chung, and B. Raghothamachar, Materials Science & Engineering Department, State University of New York at Stony Brook, Stony Brook, NY 11794-2275 USA

Four CdZnTe crystals grown in microgravity (-g) were analysed with respect to hydrostatic and buoyant gravitational influences. Characterization was conducted utilizing optical and infrared microscopy, differential chemical etching, FTIR spectroscopy, x-ray rocking curve and precision lattice parameter mapping, and x-ray synchrotron topography. It was found that in the absence of hydrostatic pressure the liquid separated from the ampoule walls, depending on influences including: volumetric fill-factor, level of constraint, residual g-vector, ampoule geometry and growth conditions. Regions solidified without wall contact were found to virtually eliminate twinning, which is pervasive terrestrially. This suggests that many of the twinning defects are surface nucleated, and nucleation and/or multiplication is furthered by stiction at the ampoule/crystal wall. Further, the regions solidified without wall contact showed dramatic reductions in (111)[110] dislocation density, from 800,000 400,000 (1-g) to 800 400 (-g) epd. This was largely attributed to reduction in hoop stresses within the flight samples during growth and post-solidification cooling. Regions of partial wall contact showed defect gradients, with high densities on the wall side and low densities on the free surface side. These results are consistent with our our original experiment hypotheses and are in excellent agreement with predictions from our high-fidelity thermal and thermo-mechanical stress models. Synchrotron reflection topographs of the sample surfaces, synchrotron transmission and reflection topographs of selected chemo-mechanically polished wafers, and Bragg contour maps of the residual strains within the one-g and -g crystals will be presented and explained on the basis of output of the thermo-mechanical process model.