Conduction and charge trapping in polysilicon-silicon nitride-oxide-silicon structures under positive gate bias

Carrier conduction and trapping in silicon-nitride-oxide-silicon SNOS structures has been studied under positive gate bias using current-field (I vs. E) characteristics and flat-band voltage shift-fluence (ΔV_FB vs. F) for structures with a thick bottom oxide (>100 Å). Under these conditions evidence is found of electrons tunneling from the Si through the bottom oxide, and holes injected from the gate moving through the nitride with recombination occurring in the nitride layer. Trapping of both electrons and holes is significant and the saturation value of the flat-band voltage shift is shown to depend parabolically on the thickness of the nitride layer. A simple two-carrier conduction model is proposed to explain the observed conduction and trapping characteristics. It is also shown that holes are the dominant conduction carriers in polysilicon-silicon nitride-silicon (SNS) structures under both positive and negative gate-bias conditions