THEORY OF HYDROGEN INTERACTIONS WITH AMORPHOUS SILICON

We present an overview of recent results for hydrogen interactions with amorphous silicon (a-Si), based on first-principles calculations. We review the current understanding regarding molecular hydrogen, and show that H2 molecules are far iess inert than previously assumed. We then discuss results for motion ofhydrogen through thematerial, as relating to diffusion and defect formation. We present a microscopic mechanism for hydrogen-hydrogen exchange, and examine the metastable ~SiH2 complex formed during the exchange process. We also discuss the enhanced stability of Si-D compared to Si-H bonds, which may provide a means of suppressing light-induced defect generation. iNTRODUCTION We have recently witnessed a resurgence of interest in the properties of hydrogen in semiconductors in general, and in amorphous silicon in particular. Several exciting devel-opments have spurred this renewed interest: focusing on a-Si, they include new informa-tion about Si-H bond dissociation, hydrogen diffusion, and new models for light-induced defect generation; the potential for more stable defect passivation by using deuterium in