Defect transition energies and the density of electronic states in hydrogenated amorphous silicon

Using photoluminescence excitation (PLE) spectroscopy, we report detailed measurements of the fundamental absorption threshold below the optical gap in hydrogenated amorphous silicon (a-Si:H). These measurements suggest that the density of neutral defects is much greater than the densities of charged defects in intrinsic a-Si:H. The positions and widths of the corresponding transition energies are determined and agree with two models proposed to describe the density of states in a-Si:H.