On weakly dispersive multiple-trapping transport

Equations for multiple-trapping carrier transport, corresponding to the time-of-flight method are approximately solved under the assumption that the majority of carriers are in a thermal quasi-equilibrium. The solutions show a Gaussian shape of the carrier packet. The mean velocity of the carrier sheet for the dispersive transport regime decreases in time and its dispersion grows faster than the square root of time. The accuracy of the obtained formulas is verified by Monte Carlo calculations for exponential and Gaussian trap distributions. A satisfactory agreement is obtained up to the effective carrier transit time, provided that the trap density falls-off sufficiently fast in the energy gap. A new method of determining energetic trap profiles in disordered solids from the time-of-flight measurements is proposed.