DENSITY OF SI-H BONDS RESPONSIBLE FOR STRUCTURAL FLEXIBILITY IN A-SI-H

Modulation of infrared absorption of the Si-H stretching mode followin g a modulated excitation can be observed at around 2000 cm(-1) as a ph otoinduced bleaching band in a photomodulation spectrum of a-Si:H as r eported previously by Vardeny et al. Here we have studied how this mod ulated vibrational spectrum is affected by photodegradation assuming t hat the spectral change comes from breaking of weak Si-Si bonds next t o a Si-H bond. By evaluating quantitatively the spectral change induce d by photodegradation as well as the simultaneous change of ESR spin d ensity, 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 similar to 1.4-2.4 x 10(18) cm(-3). It is interesting that the evaluated value is only about 0.024-0.04% of the total density of Si-H bonds containe d in the specimen used here. (C) 1998 Elsevier Science B.V. All rights reserved.