Steady-state photoconductivity in amorphous selenium glasses

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.