Large area silicon sheet task low-cost silicon solar array project. Fifth quarterly progress report, January 1, 1977--April 1, 1977

Abstract

The seeded growth furnace with the slotted molybdenum susceptor has been operated during the past quarter. Flat sheets of sapphire were used as the tray, and local cooling at the tin-silicon alloy surface was provided by a symmetric water-cooled jet. The silicon surface growth obtained during the past quarter has been consistently polycrystalline. This poor growth is attributed to impurities in the seeded growth furnace, caused by leakage into the system. Two sources have been identified: deteriorating neoprene O-rings and leaks of cooling water from the jet nozzle. The O-rings were replaced with indium gaskets, and the nozzle is being rebuilt. Weight loss measurements of the sapphire tray plates indicate that they suffer negligible attack by tin-silicon alloy melts at 1000/sup 0/ to 1100/sup 0/C. The growth habit of crystals nucleated spontaneously at the tin-silicon alloy melt surface has been studied. The crystal growth observed is consistent with dendritic and web growth from (111) singly twinned triangular nuclei. Examples of planar surface growth of small (less than 0.1 mm), thin crystals from these twinned surface seeds have been observed.