Dangling bonds and the Urbach tail in silicon

Electron spin resonance (ESR) and highly sensitive optical-absorption measurements have been performed on plastically deformed silicon, polycrystalline silicon, and high interface state density, oxidized silicon samples. In the first two cases, the response of the Urbach-like subgap optical absorption and the ‘‘dangling bond’’ ESR signal following thermal and atomic hydrogen anneals is found to be distinctly different from that reported previously for polycrystalline silicon. These data suggest that transitions of the dangling bond are not responsible for this Urbach-like behavior. In addition, we find that removal of the interfacial silicon dangling bond by oxide stripping results in no measurable sample absorptance decreases, implying a considerably lower optical cross section than has been previously estimated for dangling bonds in the bulk.