Density of states in the mobility gap of stabilized a-Se from electron time-of-flight photocurrent analysis

Abstract The distribution of localized states in a-Se in the upper part of the mobility gap has been investigated by comparing the measured and calculated electron transient time-of-flight (TOF) photocurrents. The theoretical analysis of multiple-trapping transport has been done by the discretization of a possible continuous distribution of localized density of states (DOS) and the use of the Laplace transform formalism. The continuous distribution of localized states has been approximated in the interval [ E c , E c −0.6 eV] by a spline function passing through nodes, whose positions have been subject to optimization. Another parameter of optimization was the integrated concentration of states lying deeper than E c −0.6 eV. A possible effective DOS has the following features: a peak at ∼0.30 eV below E c with a peak at ∼10 17 eV −1 cm −3 and a shoulder at 0.45–0.50 eV below E c with an amplitude 10 14 –10 15 eV −1 cm −3 . The concentration of deep states varies from 10 11 to 10 14 cm −3 . The effects of alloying with As and doping with Cl are also investigated.