Comment on the dielectric breakdown properties, current density-voltage and capacitance-voltage characteristics of ion-beam-synthesized Si 3N 4 layers

Abstract

Some recent work by Yadav and Joshi on ion-beam-synthesized Si 3N 4 layers has suggested that below the nitride layer an amorphous silicon layer is formed. Electrical conduction through the layers was ascribed to space-charge-limited conduction. It is shown that a fuller analysis of the published capacitance-voltage characteristics indicates that the nitride layer is of approximate thickness 1000 Å, while the amorphous silicon layer may either be absent or of thickness up to 2.3 μm, depending on the annealing conditions. It is confirmed that the current density-voltage characteristics indicate that space-charge-limited conduction takes place, and it is also shown that for a single discrete trapping level the trapping concentration is in the range from 3.3 x 10 19 to 3.6 x 10 24 m -3 for the amorphous silicon and from 3.4 x 10 22 to 3.7 x 10 27 m -3 for the nitride; if trapping is via traps exponentially distributed in energy below the conduction band edge the trapping concentrations are 8 x 10 27 m -3 for the amorphous silicon and 1.4 x 10 30 m -3 for the nitride. Although the latter type of trapping distribution is often observed in amorphous insulating layers, it is concluded that the high trapping concentrations calculated in the present case are unlikely to be realistic and that a more complex type of trapping distribution is probably responsible for the effects observed.