Technical Operations Support (TOPS) III. Delivery Order 0007: Chalcopyrite Crystal Growth
Final rept. 1 Nov 2005-1 Aug 2006
FISK UNIV NASHVILLE TN DEPT OF PHYSICS
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1. Chalcopyrite crystal growth - AgGaSeTe was grown via Accelerated Crucible Rotation Technique ACRT. ACRT did provide good homogeneity and elimination of bulk bubbles, however overall crystal quality was inferior to crystals grown by Horizontal Bridgman technique. The anisotropic expansion of AgGaSeTe results in better growth in horizontal configurations which leave a degree of freedom for expansion and contraction along the long, unrestricted top side of the crystal. AgGaSe2 and AgGa0.6In0.4Se2 was grown using horizontal Bridgman. Characterization via photoluminescence, optical transmission, and Raman indicate high crystal quality. 2. LiGaX2 crystal growth - LiGaTe2 and LiGaSe2 were grown using horizontal electrodynamic gradient technique with a 24-zone furnace. Li could not be obtained with purity better than 99.99. Synthesis and crystal growth were done in the same carbon-coated vessel, in order to accommodate the high reactivity of Li with the ampoule walls and with air. The LiGaTe2 crystal was of good optical quality for a first attempt at this material, however only a small single crystal could be mined from the polycrystalline ingot that resulted from the growth attempt. A larger crystal was obtained from the LiGaSe2 growth, but its optical quality was very poor. 3. GaTe crystal growth - GaTe, GaSe0.2Te0.8, GaSe0.8Te0.2, and GaSe were grown via vertical seeded Bridgman, resulting in large crystals of good quality. Optical band gaps were measured by optical transmission and photoluminescence. These results are encouraging that further work could result in a ternary crystal with improved terahertz nonlinear optical performance over GaSe.
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