Deposition and properties of microcrystalline silicon from chlorosilane precursor gases

The use of chlorosilanes (silicontetrachloride and dichlorosilane) for rf plasma-deposition of microcrystalline silicon is explored. Deposition conditions similar to those employed for high rate deposition of efficient microcrystalline silicon solar cells (frequency: 13.56 MHz, high rf power, high pressure and high hydrogen dilution of process gas) were used and high deposition rates were achieved. Silane-based materials, deposited under the same conditions, were studied for comparison. Lowest porosity is obtained for both chlorinated and unchlorinated material at a crystallinity (measured by Raman scattering) near 70%. Infrared absorption measurements indicate the presence of more void-related microstructure in chlorosilane-based material than in silane-based. Conductivity measurements give a Fermi level near midgap for an undoped chlorinated material while our silane-based samples show unintentional doping effects. By doping of chlorinated material with boron, high conductivities are obtained. Chlorinated material was successfully incorporated as p-layer in microcrystalline Si solar cells.