Crystallographic properties of grain size-controlled polycrystalline silicon thin films deposited on alumina substrate

In order to obtain higher performance of polycrystalline silicon (poly-Si) thin film devices, crystallinity of poly-Si thin films should be enhanced. In this study, poly-Si thin films with thickness of 10 μm heading for the solar cell application were thermally deposited onto alumina substrates with in-situ grain size controlling by using the intermittent source gas supply method to reduce grain boundaries. By changing source gas supply condition, the grain size was controlled in the range of a few μm to over 10 μm. Improvement of crystallinity of poly-Si thin films could be observed with grain size enlargement. The peak position and width of Raman TO-LO peak at around 520 cm−1 of small-grained sample showed larger shift from ideal value of c-Si, but becoming closer to c-Si with grain size enlargement, indicating stress relaxation. In photoluminescence measurement, intensity of TO-BE peak which indicates the crystallinity increased with grain size enlargement. These crystallinity improvements with grain size enlargement resulted in increasing of carrier mobility of poly-Si thin films from 20 to 40 cm2/V s.