Transient photomodulation spectroscopy of nanocrystalline hydrogenated silicon

Transient photomodulation spectra were measured on nanocrystalline Si:H films in the time domain from 10-7 to 10-2 s, spectral range from 0.25 to 1.25 eV, and temperature range from 80 to 300 K. The properties of the spectra are compatible with the presence of two phases, amorphous and crystalline. The amorphous phase is similar to a-Si:H. Photoinduced free-carrier absorption is associated with the crystalline phase; its decay is described by a stretched exponential which extends into much longer times than the exponential decays in crystalline Si. A model for the recombination process is proposed.