Long-time transient conduction in a-Si:H p─i─n devices

Measurements are reported of the time-varying reverse-bias current in p─i─n devices made from hydrogenated amorphous silicon. Two mechanisms of current flow are identified, corresponding to the thermal generation of charge from states near the middle of the gap, and the injection of charge from the contacts. The temperature and time dependence of the thermal generation current allows the deep depletion quasi-Fermi energy and the depletion charge to be determined. Measurements of the slow transient currents from junction-recovery experiments give information about the density of states distribution near mid-gap. The contact injection current exhibits a bias-induced metastability which is annealed at elevated temperatures.