Photo-Induced ESR in Amorphous C:H Films Prepared by Glow Discharge Decomposition of CH₄ and H₂

Hydrogenated amorphous carbon films with a high content of sp 3 bonds were prepared by a glow-discharge-decomposition of CH 4 and H 2 mixture. With exposure to light at 77 K, the films exhibit a new ESR signal with g =2.011 and a half width of 23 G in addition to an enhancement of the signal at g =2.003 due to C dangling bonds. The new signal is attributable to trapped holes in the valence-band-tail-state, and its density decreases with increasing hydrogen content in the film.