High-field hopping transport in band tails of disordered semiconductors

Interplay between temperature T and high electric field F concerning their influence on the hopping transport in disordered semiconductors is studied theoretically. A series of computer simulations of transient and steady-state conduction is carried out with emphasis on the verification of the concept of the so-called effective temperature. According to this heuristic concept the influence of T and F can be parametrized by a single quantity ${\mathit{T}}_{\mathrm{eff}}$(T,F). We show that such functions ${\mathit{T}}_{\mathrm{eff}}$(T,F) do exist for both transient and steady-state phenomena; however, they do not coincide with each other for these two cases, implying that there is no universal effective temperature for all transport phenomena. This conclusion is supported by a calculation of the conducting path of carriers under the influence of a high electric field. Theoretical results obtained provide rather a good understanding of experimental data available.