Current transport and instability mechanisms in thin film diodes with nonstoichiometric silicon nitride(a-SiNx:H)semiconducting layers have been investigated. In common with amorphous silicon thin film transistors the electrical characteristics of these diodes have been found to drift during use. We found that the initial current-voltage characteristics are related to the choice of interfacial treatments. This is explained by trapping of electrons at interface defect states and by tunneling of electrons into the conduction band via these states. We have also found a relationship between the initial characteristics of the diodes and the rate of drift due to electrical stressing. A threshold exists below whose drift is independent of the current-voltage characteristics and above which there is a strong dependence. This dependence of drift on current-voltage characteristic is consistent with field enhanced defect creation in thea-SiNx:Hlayer. ©1997 American Institute of Physics.