Photoluminescence excitation spectroscopy ina-Si:H: Evidence for phonon-assisted absorption

Photoluminescence in a-Si:H has been investigated using optical excitation energies ${\mathit{E}}_{\mathit{x}}$ varying from 1.27 to 2.0 eV. At low temperatures (T<100 K) a strong dependence of both the radiative quantum efficiency and the energy distributions of photoexcited carriers on ${\mathit{E}}_{\mathit{x}}$ has been observed for ${\mathit{E}}_{\mathit{x}}$200 K), the dependence of the energy distribution of carriers on ${\mathit{E}}_{\mathit{x}}$ disappears within a narrow interval of temperature. A model of phonon-assisted absorption is proposed to account for the experimental results.