Hydrogenated amorphous silicon films obtained by a low pressure dc glow discharge

Films of a-Si: H have been deposited by means of a dc hot cathode discharge of SiH₄ with electrostatic confinement at a pressure as low as 0.4 Pa. The plasma used is quite quiescent as has been observed by means of reproducible Langmuir probe measurements. Substrates have been placed at different locations in between the electrodes, some of them facing the anode and the others facing the cathode.Films deposited on substrates facing the cathode present a granular, non-columnar, structure, an IR spectrum with only SiH absorption peaks, and a very low photoresponse. Films deposited on substrates facing the anode have a similar IR spectrum but are homogeneous, have lower hydrogen content, and present a high photoresponse. The optical absorption coefficient shows in all samples thenE=C(E–E₀) ^x behaviour, but with exponentx=3 and notx=2 as is usually considered in a-SiH.