Deposition of highly photoconductive wide band gap a-SiOx:H thin films at a high temperature without H2-dilution

Electrical and optical characterisation of hydrogenated amorphous silicon-oxygen alloy thin films (a-SiOx:H, x<2) grown in a single chamber radio frequency plasma enhanced chemical vapour deposition (PECVD) system at a high substrate temperature of 300 °C is presented. The samples were investigated by Fourier transform infrared spectroscopy (FTIR), optical transmission, the constant photocurrent method (CPM), conductivity and steady-state photoconductivity measurements. With increasing oxygen concentration, the Tauc gap increases from 1.69 to 2.73 eV. The sample with an oxygen concentration of 26.2 at% and a reasonably high bandgap of 2.18 eV shows photoconductivity comparable to that of pure a-Si:H films. The Urbach parameter (E0) increases almost linearly with oxygen concentration whereas the dangling bond defect density is found to be saturating at a value of about 7.1×1016 cm−3. One of the highly alloyed samples with E0=123meV exhibited a detectable photosensitivity.