Amorphous silicon-oxygen alloy films with various composition have bee
n prepared by r.f. glow discharge decomposition of SiH4 and CO2 gas mi
xtures. The analysis of infrared absorption spectra and x-ray photoemi
ssion spectra shows that the film consists of two phases, a silicon-ri
ch phase and an oxygen-rich phase. We suggest that this two-phase stru
cture results in the high photoconductivity with wide optical gap in t
hese films.