Electron transport in disordered semiconductors studied by a small harmonic modulation of the steady state

Semiconducting or insulating networks form a class of disordered systems in which electron motion can be attenuated by scattering effects (structural disorder) and multiple trapping (electronic disorder). We studied the electron transport characteristics of such a disordered system under steady-state constraints by introducing a small excess of free carriers, harmonically varying in time. Propagation of this small excess through the system is considered taking into account scattering and temporary localization. Finally, the harmonic photocurrent response upon light modulation is considered. Two different transport regimes could be distinguished. In the first regime transport appears to be regular and is characterized by a single transit time for all elections. However, the transit time may be determined by multiple trapping. Scattering and multiple trapping can be distinguished by variation of the steady-state constraints. The second (irregular) regime shows a strong dispersion in the transit time, similar to dispersive transport observed under nonsteady-state conditions.