Dangling-bond relaxation and deep-level measurements in hydrogenated amorphous silicon

We present a new perspective on defect levels in hydrogenated amorphous silicon (a-Si:H) that unifies relaxation effects inferred from two recent experiments. In particular, we show how earlier calculations of dangling-bond relaxation can account for both the level deepening effect reported in transient capacitance measurements and the shallowing effect reported in transient photocurrent measurements under optical bias. The former is due to dangling-bond relaxation toward a pyramidal bonding configuration, and the latter to relaxation toward a planar configuration. We comment on the many-body nature of the remarkably slow kinetics of defect relaxation.