Single crystal growth of semiconductors and defect studies via positron annihilation spectroscopy

Small single crystals of Ga 2 ( Se x Te 1 a x ) 3 semiconductors, for x=0.1, 0.2, 0.3, were obtained via modified Bridgman growth techniques. High resolution powder x-ray diffractometry confirms a zincblende cubic structure, with additional satellite peaks observed near the (111) Bragg line. This suggests the presence of ordered vacancy planes along the [111] direction that have been previously observed in Ga 2 Te 3 . Defect studies via positron annihilation spectroscopy show an average positron lifetime of a 400 ps in bulk as-grown specimens. Such a large lifetime suggests that the positron annihilation sites in these materials are dominated by defects. Moreover, analyzing the electron momenta via coincidence Doppler broadening measurements suggests a strong presence of large open-volume defects, likely to be vacancy clusters or voids.