Thickening of thin laser crystallized silicon films by solid phase epitaxy for photovoltaic applications

Abstract

Multicrystalline silicon films up to 2μm thick with grain sizes up to 100μm were prepared on glass substrates by laser crystallization followed by solid phase epitaxy of electron beam deposited amorphous silicon (a-Si) at 600°C. The dependence of the epitaxial growth rate on the crystallographic orientation was investigated. While grains with <100> orientation with respect to the surface normal show the highest growth rate, <111>-grains tend to grow the slowest. Furthermore, we studied the kinetics of the solid phase growth depending on the deposition conditions of a-Si. For this purpose we implemented a simple measurement system that determines the transmittance of the c-Si/a-Si layer stack during furnace annealing at a wavelength of 808nm. Fastest growth is obtained for a-Si deposited at highest rates at a temperature of 300°C. Further increase of the deposition temperature prevents epitaxy. Interface cleaning deserves particular care since contaminations at the interface lead to a retardation time for solid phase epitaxy.