Gap states and stability of rapidly deposited hydrogenated amorphous silicon films

Abstract

The sub-band gap absorption spectrum α( hv) in a-Si:H films prepared at high deposition rates was measured by the constant photo-current method (CPM) for photon energy ranging from 0.8 to 1.7 eV in a thermally-annealed state and light-soaked state. The Simmons–Taylor theory and occupation statistics of correlated defects are used to model the distribution of band tail and gap states. It is found that the density of gap states increases after light soaking, however, there is no evident change found in the density and distribution of band tail states. Measurements of the light-induced changes find that the photoconductivity decreases by less than one order of magnitude after long time of light illumination for the high rate deposited a-Si:H. This demonstrates that the high rate deposited samples have relatively high stability compared with conventionally deposited a-Si:H.