CONTACT LIMITATION OF SECONDARY PHOTOCONDUCTIVITY IN INTRINSIC A-SI-H

A requirement for secondary photoconductivity is that the supply of cu rrent by the contacts is sufficient to keep the photoconductor neutral . This requirement is not fulfilled under most experimental conditions in intrinsic a-Si:H at and below 300 K. We find a positive space char ge and a large voltage drop near the cathode which yield a subohmic ph otoconductivity in the range of thermal quenching at applied fields in excess of 100 V/cm. The onset of the subohmic region moves to larger fields with light soaking. (C) 1998 Elsevier Science B.V. All rights r eserved.