Local bonding of oxygen and hydrogen in a-Si:H:O thin films

This paper provides a structural interpretation for the O-induced IR absorption bands in a-Si:H:O alloys. For films with C(O)∼0.1 to 5.0 at.% and C(H)∼10 at.%, there are three O-related IR features, at 2090, 980, and 780 cm−1. These are assigned to a local atomic arrangement in which the H and O atoms are bonded to a common Si site. The mode at 780 cm−1 strongly couples Si–H and Si–O–Si motions and is a unique signature of a particular local geometry. The other two vibrations are decoupled Si–H (2090 cm−1) and Si-O-Si (980 cm−1) stretching motions whose frequencies are perturbed by near-neighbor induction effects. Substitution of D or F for H changes the degree and character of the coupled mode, while substitution of Cl removes it completely.