Density of Si–H bonds responsible for structural flexibility in a-Si:H

Abstract

Modulation of infrared absorption of the Si–H stretching mode following a modulated excitation can be observed at around 2000 cm−1 as a photoinduced bleaching band in a photomodulation spectrum of a-Si:H as reported previously by Vardeny et al. Here we have studied how this modulated vibrational spectrum is affected by photodegradation assuming that the spectral change comes from breaking of weak Si–Si bonds next to a Si–H bond. By evaluating quantitatively the spectral change induced by photodegradation as well as the simultaneous change of ESR spin density, density of Si–H or weak Si–Si bonds, which are precursor sites for structural flexibility in a-Si:H, can be evaluated to be ∼1.4–2.4×1018 cm−3. It is interesting that the evaluated value is only about 0.024–0.04% of the total density of Si–H bonds contained in the specimen used here.