Thermal and Optical Quenching of the Photoconductivity in a-Si:H-Films

Abstract

It is shown that there are major inconsistencies in the current interpretations of optical and thermal quenching of the photoconductivity in a-Si:H. In this report the quenching phenomena are studied in differently doped samples and in the accumulation layer of a field effect transistor where the occupancy of the centers can be controlled by the gate potential. It is found that optical and thermal quenching arise from different excitation processes: Thermal quenching, which is only observed in samples where the Fermi level is close to midgap, is attributed to the temperature enhanced transfer of holes to D~-states; optical quenching is suggested to arise in all kinds of samples from the excitation of electrons from D“-states, and its temperature dependence is shown to originate from the competition of direct capture of electrons into neutral dangling bonds with tunneling transitions of band tail electrons.