Amorphous Silicon Films from Dichlorosilane and Hydrogen

Abstract

ABSTRACTWe deposited a-Si:H thin-films by PECVD of dichlorosilane (SiH2Cl2) diluted with H2 in a DC-triode glow-discharge reactor. The dilution ratio, given as the ratio of H2 to SiH2Cl2 flows, was varied from 0 to 130 and the pressure was varied from 0.3 to 0.75 Torr as the hydrogen fraction was increased. We report on the properties of the deposition plasma and the resulting films; namely the plasma pressure-voltage characteristics and the films' chemical composition, structure, and optoelectronic properties. For hydrogen dilution ratios greater than 2:1, dense, rigid films are deposited, with optical bandgaps from 1.75 to 1.9 eV. With increasing hydrogen dilution a growth rate of 5 Å/s is maintained while photoconductivities increase and defect densities decrease. The best films are obtained at a dilution ratios of 16:1 to 32:1, where we have obtained a dark conductivity of 10−13 S/cm, a photoconductivity of 2×10−7 S/cm (at G=1020 cm-3 s−1) and a defect density of 1.5×1016 cm−3.