Published online by Cambridge University Press: 25 February 2011
The ideas and energy diagrams of the valence alternation pair model (also: negative-U model) are introduced and matched to the classical steady-state photoconductivity analysis in terms of two discrete recombination levels in the gap. Data from bulk a-As47Se53 serve as example. Negative effective correlation energies Ueff = -0.72 eV for a-As2Se3, −0.61 eV for a-As2Se4 and -0.58 eV for a-As47Se53 are obtained. The positively charged defects are found to be Se3+ with relaxation energies W+ ≃ 0.1 to 0.2 eV, and the negatively charged defects are As2− with relaxation energies W− ≃ 0.3 to 0.6 eV.