Optical absorption and electrical conductivity of microcrystalline silicon layers grown by SiF4-H2 plasma on glass substrates

Microcrystalline silicon mc-Si. films, having different crystalline fractions (fc) and thicknesses, were deposited on glass by plasma enhanced chemical vapor deposition (PECVD) starting from a SiF4-H2-He gas mixture. The absorption coefficient (alfa) in the energy range 0.8-2.0 eV was evaluated from the standard constant photocurrent method (S-CPM) and dark conductivity measurements have been performed. The S-CPM data elaboration was carried out according to the Favre approach, in order to take account for the bulk scattering. The true alfa vs. energy trend was interpreted to evidence defect density and the crystalline-amorphous fraction of the samples. However, no thickness effect on the true alfa coefficient was observed, whereas the change in crystalline fraction resulted in different scattering effects.