Surface photo-voltage spectroscopy was used to determine the positions of deep defect state levels in undoped hydrogenated amorphous material. The occupied and empty levels were identified, with a clear advantage over existing methods. The identification of the levels, and the effect of light-soaking upon their concentrations, provided direct experimental confirmation of the main features which were predicted by thermal equilibrium models. The identification of other levels in amorphous materials with greater disorder further supported a proposed potential fluctuation model.

E.Fefer, Y.Shapira, I.Balberg: Applied Physics Letters, 1995, 67[3], 371-3