Analysis of dispersive transport in amorphous semiconductors by discretization of a continuous distribution of localized states

It is shown that most features of anomalously dispersive multiple-trapping transport in amorphous semiconductors can be calculated easily and accurately when the density of localized states is represented by a set of discrete levels. Calculation of the transient current, the occupation of the conduction band and the trapping levels, when the trap parameters are known, reduces to a set of simple matrix operations. The same holds for the solution of the inverse 'spectroscopic' problem; that is, given the transient photocurrent, for obtaining the distribution of localized states. For the last problem, it is shown very clearly that a given transient photocurrent cannot be interpreted unambiguously by a definite density-of-states distribution, thus the limitations of 'transient photocurrent spectroscopy' are neatly illustrated. The use of discrete levels also allows one to obtain an approximation to the transit time in a time-of-flight experiment, as shown earlier by Schmidlin (1977).