Zone melting recrystallization of microcrystalline silicon ribbons obtained by chemical vapor deposition

Abstract

We present the results achieved with an optical zone melting recrystallization (ZMR) system, which concentrates the radiation of two halogen lamps on the surface of a microcrystalline silicon (µc-Si) ribbon sample, creating a long, 2 mm width molten region (∼1414° C). µc-Si ribbon samples measuring up to 25×100 mm2 were previously obtained using an inline optical chemical vapor deposition (CVD) system, that grows silicon layers on top of a silicon dust substrate. Inside the ZMR system, the µc-Si ribbon sample is recrystallized in an argon atmosphere and using a step motor to pull the ribbon at a constant speed between 1 to 6 mm/min, the molten zone travels along the ribbon, recrystallizing the whole sample into a multi-crystalline silicon (mc-Si) ribbon, with an average crystal size in the [1; 10] mm range. It was observed that the physical characteristics of the µc-Si ribbon, like powder substrate incorporation, porosity, thickness, powder grain size used as substrate in the CVD step, have a crucial influence on the recrystallization process and on the electrical properties of the mc-Si ribbon obtained after the ZMR process. Lifetime measurements performed on the recrystallized samples suggest that improvements regarding crystalline quality and possible presence of impurities need to be addressed.