Luminescence in amorphous semiconductors

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Abstract
A review of the luminescence properties of amorphous semiconductors is presented. The materials covered are chalcogenide glasses, silicon and arsenic. Luminescence spectra, excitation spectra, temperature dependences and lifetimes are described. The radiative transition in chalcogenides is the recombination of an electron in the conduction band tail and a trapped hole. A strong electron-phonon coupling distorts the lattice near the trapped hole, lowering its energy. This interaction is responsible for the broadness of the luminescence band and its position at about half the band gap energy. The recombination centre is thought to be a charged dangling bond with density 1017 cm-3 in arsenic chalcogenides and 1016 cm-3 in selenium. The same centre is observed in the hole drift mobility, and thermally stimulated conductivity. Luminescence in amorphous silicon also originates from recombination between the band tails and deep centres, with three separate transitions identified. In contrast to chalcogenides the electron-phonon coupling is not strong. The shape and intensity of the spectra are very sensitive to sample preparation and treatment, and correlate with other electrical and optical properties of Si.