The light-induced metastable lattice expansion in hydrogenated amorphous silicon

A new insight of the light induced metastable lattice volume change is pres ented for a-Si:H prepared by plasma enhanced chemical vapor deposition (PEC VD). The laser optical-lever bending method is demonstrated for detecting a volume change of film semiconductors. The observed light-induced expansion is persistent after light soaking and is recovered by thermal annealing at 200 degrees C for 2 h. The light exposure time dependence of the lattice e xpansion was the same dependence of the photoconductivity and light-induced defect density. A correlation between the light-induced expansion and the photolitic changes is obtained. The experimentally obtained light-induced e xpansions normalized by the initial volume, Delta V/V are the order of 10(- 6)-10(-5), which is two orders smaller than for chalcogenide glasses such a s a-As2S3. The Delta V/V has a maximum at deposition temperatures between 2 00 degrees C and 300 degrees C. The Delta V/V is a maximum at hydrogen dilu tion ratio with silane gas, r =similar to 12, but the microcrystalline sili con at r = 39 has a negligible small Delta V/V It is demonstrated that the light-induced expansion is from the structure of a-Si:PI. (C) 2000 Elsevier Science B.V. All rights reserved.