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

Multicrystalline silicon films up to 2 μm thick with grain sizes up to 100 μm 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 <1 0 0> orientation with respect to the surface normal show the highest growth rate, <1 1 1>-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 808 nm. 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.

► Solid phase epitaxy of silicon on laser crystallized seed layers is demonstrated.
► In situ microscopy confirms the dependence of growth rate on crystal orientation.
► Cleaning of the seed layer surface is essential for fast growth due to retardation.
► High deposition rates and deposition temperatures of 300 °C maximize growth rate.