Journal of optoelectronics and advanced materials vol:4 issue:4 pages:837-842
Charged co-ordination defects that contribute discrete electronic energy levels to the distribution of localized states in the band gap have been widely accepted as part of the negative-U model for chalcogenide glasses. However, since the density of these defects is lower than the density. of localized tail states they fail to be resolved in direct optical spectroscopy. It is argued that, contrary to a recent suggestion and with the overwhelming evidence in their favour, this fact is not sufficient grounds for doubting the presence of the charged defects.