Gap states and stability of rapidly deposited hydrogenated amorphous silicon films

The sub-band gap absorption spectrum alpha(hv) in a-Si:H films prepared at high deposition rates was measured by the constant photo-current method (CP M) for photon energy ranging from 0.8 to 1.7 eV in a thermally-annealed sta te and light-soaked state. The Simmons-Taylor theory and occupation statist ics of correlated defects are used to model the distribution of band tail a nd gap states. It is found that the density of gap states increases after l ight 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 magnit ude after long time of light illumination for the high rate deposited a-Si: H. This demonstrates that the high rate deposited samples have relatively h igh stability compared with conventionally deposited a-Si:H. (C) 2000 Elsev ier Science S.A. All rights reserved.