Electric-field-dependent dispersive transport of carriers in band tails of low-dimensional systems

A theory for the dispersive transport of carriers in the presence of an electric field for the quasi-one-dimensional systems has been developed. It is assumed that localized states are distributed randomly in both space and energy coordinates and that hopping of the carriers occurs in both coordinates. The exponential form of the density of states for band tails is considered. Expressions for the time-dependent demarcation energy and mobility are calculated. The theory predicts that the mobility has three power-law decay branches with exponents nm 1, mm 1 and mm m1. Here nand mare directly proportional to the temperature and electric field respectively. The first power law is associated with the multiple-trapping mechanism and is well known. The other two power laws are new findings of the present theory. The time-of-flight experiments for hydrogenated amorphous SiN x Si/hydrogenated amorphous multilayers can be understood by the present theory on the qualitative basis.