Abstract
The authors report photoemission results from which we directly detemined the density of states g(E) in the gap of a-Si:H between the top of the valence band E sub(V) and the Fermi level. At 0.4 eV above E sub(V), g(E) was found to be similar to 1x10 super(20) cm super(-3) eV super(-1) in the updoped film; P-doping increased g(E) in this region whereas annealing reduced it. The photoconductivity-derived optical absorption spectrum matched the shape of the photoemission spectrum, and thus supports the explanation that the photoconductivity shoulder at photon energies in the region of 1.3 eV is due to transitions from localized states above the valence band to the conduction band.