Density of states in hydrogenated amorphous germanium seen via optical absorption spectra

We propose and discuss a deconvolution procedure to analyze quantitatively optical absorption spectra. This procedure is used to determine the density of states distribution in the mobility gap of a-Ge:H films studied by a combination of standard optical transmission measurements, photothermal deflection spectroscopy and constant photocurrent method. This yields a Gaussian distribution for the gap states centered at ED=(0.60±0.01) eV below the conduction band edge, with a width at half height equal to (0.32±0.01) eV. A good linear correlation is also observed between the deep-defect density ND and the corresponding absorption coefficient at a photon energy of 0.7 eV.