Improvement in the properties of a-SiGe:H films: Roles of deposition rate and hydrogen dilution

Abstract

Device quality a-SiGe:H thin films have been deposited by radio-frequency plasma-assisted decomposition of silane and germane diluted with and without hydrogen. Improvement in structural and electronic properties have been achieved employing low deposition rate and high hydrogen dilution. It has been observed that low deposition rate can reduce the preferential attachment of H to silicon throughout the alloy region while the beneficial effect of hydrogen dilution is more effective in a low band gap region (Eg≤1.40 eV). The photoconductivities of the good quality a-SiGe:H alloy films under white light illumination (50 mW/cm2) are 1.34×10−4 S cm−1 and 1.9×10−5 S cm−1 at the optical gaps of 1.51 and 1.35 eV, respectively. The changes in midgap defect density and tail states have been correlated with the photoconductivities of the samples deposited under different conditions. An attempt has been made to explain the results from the growth kinetics of the films.