PHOTOCONDUCTIVITY OF INTRINSIC AND NITROGEN-DOPED HYDROGENATED AMORPHOUS-GERMANIUM THIN-FILMS

In this work the effects of nitrogen doping on the photoconductivity of hydrogenated amorphous germanium (a-Ge:H) thin films are presented and discussed. The quantum efficiency-mobility-lifetime (etamutau) product of majority carriers has been measured as a function of light intensity in samples containing different dopant concentrations. It has been found that, for low dopant concentrations, the incorporation of nitrogen atoms in hydrogenated amorphous germanium films enhance the photoconductivity, as expected from n-type doping in tetrahedrally coordinated amorphous semiconductors. The results have been explained in terms of changes in charge distribution in the mobility gap on doping. The sensitization depends on the position of the Fermi energy, the maximum being at around E(c) - E(F) less-than-or-equal-to 0.2 eV, which corresponds to a nitrogen content of approximately 0.03 at %. The recombination kinetics for N-doped samples is always dominated by a monomolecular process, a consequence of the rather large density of electron states in the pseudogap of a-Ge:H.7594662466