Reverse current mechanisms in amorphous silicon diodes

We analyze the dark steady-state reverse current of a-Si:H nip diodes at high voltages. The reverse current shows a strong voltage dependence and has a temperature dependence characterized by a voltage-dependent activation energy. A model, based on the simultaneous field enhanced generation of electrons and holes, is developed to describe this voltage and temperature dependence. In this model the effective mass of electrons and holes is a model parameter. Good fits with experimental results are obtained for an effective mass value of 0.05me. The low effective mass value is tentatively explained as a parameter that accounts for a field dependent narrowing of the band gap due to the presence of localized band tail states.