Modelling of trap-assisted carrier transport in a-Si

A good understanding of internal properties and external characteristics yielding to optimised a-Si device structures needs an adequate modelling of a-Si material parameters and of structures made from a-Si. The existing models for transport phenomena analysis in a-Si assume that only mobile charge carriers in the conduction and valence band contribute to the carrier transport in a-Si. In the presented work a new model is proposed in which the lateral transport of charge carriers is treated in a similar way as the capture-emission transitions in the SRH approach. In this way tunnelling rates from transport edges to traps are expressed by an appropriate capture cross-section, by velocity of carriers in the direction of electric field, by tunnelling transparency of potential barrier and by concentrations of free and trapped carriers. The tunnelling and thermal capture, as well as emission rates of carriers to and from localised states in the gap determines the occupancy function in the mobility gap of a-Si. The lateral carrier transport and generation-recombination dynamics are expressed by virtue of occupancy function and the continuous distribution of localised states in the gap of a-Si.