Influence of Surface States on Distribution of Localized States Determined from Time-of-Flight and Transient Photodecay Technique in a-As₂Se₃

Abstract

The energy distribution of localized states in amorphous As₂Se₃ (a-As₂Se₃) has been extensively studied in terms of a time-of-filght (TOF) or a transient photodecay (TPD) technique. Although the exactly same behavior is expected of TOF and TPD photocurrent transients in the light of a trap-controlled band transport theory, in which homogeneous spatial distribution of localized states is explicitly assumed, the respective shape of the experimentally obtained TOF and TPD photocurrent is different. This leads to considerable controversy with respect to the distribution of localized states even in a prototypical amorphous chalcogenide, a-As₂Se₃. In this paper, the influence of surface states on current transients is examined via computer simulation based upon the trap-controlled band transport theory. The surface states are taken into account by increasing characteristic temperatures of exponential distributions of localized state at the surface region. It is demonstrated from the simulation that the disagreement between the TOF and the TPD transients can be resolved by introducing the surface states.