Development of Photo-Voltaic Cells using III-V Alloy Semiconductors for Thermo-Photo-Voltaic Applications (2004)

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The main objectives of the on going research are to develop new techniques to grow homogeneous In_xGa_<1-x>As and In_xGa_<1-x>Sb ternary bulk crystals and high quality epitaxial layers for the fabrication of Thermo-Photo-Voltaic (TPV) energy conversion system. In this aspect, the following experiments have been carried out and analyzed.1.The crystallization process of In_xGa_<1-x>Sb crystals has been investigated under microgravity in an airplane and a drop tower experiments. It is observed that the shape of solid-liquid interface and the composition profile of the crystals are influenced by gravity. Simulation results have shown that the effects of solutal natural convection and solutal Marangoni convection are very significant during the growth of the crystals.2.Homogeneous In_xGa_<1-x>Sb bulk crystals have been grown on GaSb or InSb seeds by cooling source and seed crystals at the optimized value estimated from the temperature gradient in the solution and the growth rate. In_xGa_<1- … More x>As single crystals with x values up to 0.12 were grown on GaAs seed by Rotational Bridgman method. The x values of the grown crystals are found to be homogeneous due to the feeding of GaAs source materials continuously into the In-Ga-As solution.3.Bridge layer growth technique has been successfully employed to realize high quality epitaxial layers of In_xGa_<1-x>As on patterned III-V binary substrates. For the growth of In_xGa_<1-x>As epilayers with high indium composition, a novel technique named as "composition conversion" has been successfully utilized. High quality epilayers have been grown with indium composition as high as 80%. Furthermore, the origins of the conversion mechanism have been studied in detail.4.Two selective growth techniques have been developed for the first time to grow In_xGa_<1-x>Sb and In_xGa_<1-x>As pyramidal epilayers with low etch pit density on III-V substrates viz., hollow pyramidal epitaxy technique, and the combination of composition conversion and hollow pyramidal epitaxy technique. In order to make use of the pyramidal epilayer for fabrication of optical devices, the effect of Te impurity on the structural properties of GaSb pyramidal epilayer has been studied in detail.5.p-type GaSb epilayers have been grown on n-type GaSb substrates by Zn diffusion technique. The composition profiles of the epilayers were obtained under various annealing conditions. Less