THE SIOX-HY THIN-FILM SYSTEM .2. OPTICAL BANDGAP BEHAVIOR

Variations in the optical bandgap (ETauc) with hydrogen alloying for four series of rf-sputtered a-SiOx:Hy thin films corresponding to x = 0, 0.7, 1.1 and 1.5 are reported. Within any series the Tauc gaps widen with hydrogenation in a manner similar to that in a-Si:H films. However, this widening behavior becomes less pronounced as x increases, and is hardly discernable in x = 1.5 series. The observed trends are explained by reference to studies of a-Si:H films and the theoretical a-SiOx density of states structure. It is proposed that the gap widening occurs by essentially the same mechanism as in amorphous solicon. The decrease in the phenomenon for high-x films is attributed to the lower density of Si-derived states in the gap for such films. © 1990.