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Photoluminescence absorption spectroscopy in a-Si:H and related alloys

The absorption of photoluminescence, which travels along the length of the film, has been measured in intrinsic hydrogenated amorphous silicon (a-Si:H), boron-doped a-Si:H, and related alloys in the system a a-Si1−χGeχ:H. Measurements have been performed on films of various thicknesses (about 3000 Å - 1.5 μm) as a function of temperature (4.2 - 250 K). At the higher temperatures the absorption spectra approach those which are observed by photothermal deflection spectroscopy at 300 K. At low temperatures (T ⩽ 200 K) in films of a-Si:H, a peak is observed in the sub-gap absorption about 1.15 eV. This peak, whose position is independent of temperature, is increased after irradiation at 300 K with band gap light. This peak in the absorption is difficult to detect at temperatures above about 250 K because of the increased importance of absorption in the Urbach tail near 1.15 eV as the band gap decreases with increasing temperature.

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