The transient photoconductivity of inhomogeneous amorphous semiconductors

In inhomogeneous amorphous semiconductors the energy of the lowest extended electronic states, which is called the local mobility edge, can be a function of position. As a result, charge carriers formed initially at an arbitrary point in the material will tend to move towards regions in which the local mobility edge has its lowest energy. An analysis is presented of the transient photocurrent inhomo- genous amorphous semiconductors. Model systems consisting of two distinct media are analysed in detail by means of the multi-state continuous-time random-walk method, and general formulae are derived for the transient photocurrent appropriate to various types of medium. These results indicate that, in many cases, the transient photoconductivity is determined mainly by the properties of the critical subnetwork, along which the energy of the local mobility edge does not exceed its percolation value by more than k_BT.