Low-temperature structural transitions during deposition in μc-Si photovoltaic layer deposited by VHF-PECVD

Crystallographic studies on μc-Si photovoltaic i-layer, which were prepared by VHF-PECVD (100 MHz) at a low temperature of 180 °C, have been performed employing thickness evolutions of X-ray and electron diffraction measurements. The experimental results revealed that structural uniformity along the growth direction is improved during deposition due to solid phase crystallographic transition to the (220) preferential orientation in whole region from the top to the bottom. These growth phenomena are interpreted in terms of a newly proposed model, i.e., the hybrid-phase growth model consisting of conventional vapor-phase growth at the surface plus the solid-phase crystallization occurring in the film. Moreover, we found that the structural uniformity tends to be optimum in μc-Si film optimized as a photovoltaic layer for 9% efficiency n-i-p solar cell.