Time-dependent electrical transport in amorphous solids:As2Se3

An extensive experimental and theoretical study of transient hole transport in evaporated $a-{\mathrm{As}}_2{\mathrm{Se}}_3$ unambiguously establishes that the microscopic transport mechanism is characterized by a broad distribution of individual event times. This feature leads to (i) a sample thickness and field-dependent drift mobility, (ii) an essentially featureless shape of the transient current, and (iii) a correlation between these observables. Several underlying mechanisms of transport compatible with a broad distribution of event times are detailed and critically compared with the experimental information. It is demonstrated that the interpretation of the entire field, thickness and temperature dependence of the transit time, and shape of the current pulse in terms of the widely proposed trap-controlled extended state transport (multiple-trap mechanism) leads to a number of conceptual difficulties. It is suggested that transient transport in $a-{\mathrm{As}}_2{\mathrm{Se}}_3$ be interpreted in terms of a model in which the carriers hop through localized states and possibly interact with a discrete trap level (trapcontrolled hopping). Hence, different from the multiple-trap mechanism, in the latter model dispersion is that which is already present in the microscopic transport rate itself.