Evidence for a shallow level structure in the bulk of semi-insulating GaAs

The technique of thermally stimulated conductivity is applied to the spectroscopy of shallow trap levels in semi-insulting GaAs. Twelve previously unknown conductivity peaks are reported and the activation energy for thermal release of carriers trapped in the corresponding levels are determined with the aid of Urbach’s law. The obtained values are in good agreement with results available from infrared emission and photoconductivity. It is argued that most of these levels are responsible for the unresolved Gaussian band proposed by Leach.