Steady-state photoconductivity measurements are carried out for bulk and thin-film amorphous selenium (a-Se) samples in the temperature range between 190 and 340 K. The temperature and light-intensity dependences of the photoconductivity reveal the presence of both mono-and bimolecular recombination regimes. The current activation energies measured in the two regions point to energy levels in the gap for the recombination centres at 0.36 ± 0.06 and 1.35 ± 0.10 eV above the valence band mobility edge. These values put a-Se in line with the other chalcogenide semiconducting glasses that exhibit negative-U behaviour.

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Thin films of amorphous selenium have been prepared by thermal evaporation. DC conductivity measurements were carried out on these films in the temperature range between 208 and 322 K. Above room temperature, the dark conductivity is thermally activated with activation energy E σ = 1.05 ± 0.08 eV. For temperatures below 285 K, an increase in the dark current is observed, which is interpreted in terms of a shift of the Fermi level that makes more states available for a hopping process.

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