Origin of the spectral dependence of the nonradiative efficiency in hydrogenated amorphous silicon

Measurements of the excitation kinetics and model calculations of the wavelength dependence of the room-temperature nonradiative efficiency in hydrogenated amorphous silicon (a-Si:H) are described. The nonradiative efficiency, defined as the ratio of the heat released per absorbed photon, is measured using photopyroelectric spectroscopy and displays a fairly sharp minimum when the a-Si:H is illuminated with near-band-gap photons. The results reported here indicate that this minimum arises from the variation in the amount of heat generated by free-carrier thermalization with incident photon energy.