Space-charge anomalies in insulators caused by non-local impact ionisation

Publisher Website
Google Scholar
Abstract
The non-local nature of impact ionisation is modelled using lucky-drift theory with the assumption that the relevant electric field is the average field, but that the relevant drift velocity is that associated with the local field. The carrier density relevant for impact ionisation is also taken to be non-local. The model is applied to the case of a thin film insulator, with Fowler-Nordheim injections of electrons at the cathode. For clarity's sake, the authors avoid considering the excitation of holes and limit attention to the ionisation of a set of occupied deep-level states present in high concentration. Further simplifying assumptions include the neglect of diffusion, overshoot and non-parabolicity. The authors show that the non-local nature of the ionisation process reduces the local field markedly, resulting in a pile-up of free electrons to maintain current continuity in the rest of the film. This is contrasted with the prediction of local impact ionisation theory in which the field is reduced merely to that necessary to sustain a small level of ionisation. Under certain circumstances space-charge striations are produced-this is analogous to the situation in gas discharge-and for some film thicknesses a negative differential resistance occurs.