Metastable photoexpansion of hydrogenated amorphous silicon produced by exposure to short laser pulses

The study of the metastable expansion of hydrogenated amorphous silicon after exposure to nanosecond laser pulses as well as to cw light of similar average intensity has revealed a decrease from 1 to 0.5 in the short-time power-law exponent of photon flux dependence of the effect. This transition appears at a carrier generation rate of approximately G = 1023 cm−3 s−1 and is compatible with the assumption that the underlying structural change is produced by band-to-band/tail recombination of photo-excited carriers. This view is further supported by our observation that the quantum efficiency of photoexpansion does not depend on photon energy.