Photoinduced structural instability around the Si–H bond in undoped a-Si:H and related wide-gap alloys

Abstract It is well known that a real-time change in the absorption strength of the Si–H stretching vibration is observable, when a-Si:H is illuminated at low-temperature by a modulated bandgap light. Since the Si–H stretching vibration is not directly affected by the bandgap light and is strongly localized in a-Si:H, the observed change in the vibronic absorption should be indirectly caused by some structural instability of the local environment of the Si–H bond. Therefore, the localized Si–H oscillator can serve as a detector of a dynamical structural change in its vicinity. On the basis of this idea, we have studied how the structural instability around the Si–H bond in undoped a-Si:H and related wide-gap alloys, such as a-SiN:H and a-SiO:H, differs depending on a structural configuration at the local environment of the Si–H bond.