Density of states in the pseudo-gap of amorphous silicon-germanium alloys from electrical and optical measurements

Amorphous hydrogenated silicon-germanium alloys a-Si1−xGex:H in the form of thin films were prepared by rf sputtering and chemical vapor deposition methods with x varying from 0 to 0.63. Optical transmission, reflection, and photoconductivity measurements in the visible and near-infrared regions of light enabled determination of the optical energy gap, band-tail states distribution, and density of defect states near midgap. Dark conductivity and photoconductivity were measured in the temperature range of 300–500 K. Electronic band structure (density of states versus energy) for a-Si0.74Ge0.26:H thin film was derived on the basis of optical measurements, dark conductivity, and photoconductivity.