Photochemical Vapor Deposition of Amorphous Silicon Using Mercury Photosensitization of Disilane

Abstract

ABSTRACTHigh-rate deposition of amorphous silicon films using the mercury-photosensitized reaction of disilane gas is described. The deposition rate depends upon reactant pressure, light intensity, and concentration of mercury atoms. A maximum rate of 100 nm/min is attained at a 250°C substrate temperature and a disilane pressure of 200 Pa. This rate is about 3 times higher than that for monosilane gas.Generally, the optical gap of the deposited films range from 1.7 to 1.8 eV, although the value decreases slightly with increasing substrate temperature. Photoconductivity under AM1 irradiation is 2×10−4 mho·cm−1 at a 250°C substrate temperature and the ratio of photoconductivity to dark is around 104. From the infrared data, amorphous silicon films are found to include only an SiH bond at substrate temperatures of 200° to 300°C. Hydrogen content is 10 to 13%. These data suggest that silicon films can be used in thin-film electronic device fabrication.