The theory of anomalous carrier pulse propagation in amorphous semiconductors

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Abstract
The macroscopic transport equation describing anomalous carrier pulse propagation for hopping carriers is used to calculate pulse shapes when the conductivity as a function of frequency ω is proportional to ω1 – α. For pure drift the peak of the pulse remains at the injection point when α < 0·5 and moves away when 0·5 < α < 1. The pulse shape for pure diffusion is a symmetrized and scaled version of the pure-drift pulse shape when α is halved. In a specimen of length l exhibiting a d.c. conductivity [sgrave]0 the transient current settles down to a constant value after a time proportional to ([sgrave]1/[sgrave]0)1/(1 – α), where [sgrave]1 is the a.c. conductivity at the characteristic hopping frequency. Quantitative comparison of pulse propagation and conductivity data for Se and As2Se3 indicates that different transport channels control the two effects.