In general, current transport through thin-film metal-semiconductor-metal diodes containing hydrogenated silicon-rich amorphous silicon nitride (a-SiN.c:H) is determined by electron tunnelling through the potential barriers at the metal-semiconductor contacts. After prolonged current stressing, however, there is a change in the transport mechanism and a large increase in the current. It is shown that the excess current flow is well described by field-enhanced emission of carriers via charged defect states throughout the bulk of the silicon nitride. The effect of the electric field and dependence on defect concentration is consistent with the transport of holes in the vicinity of the valence band tail. As stressing proceeds, more defect states are introduced and the conductivity of the a-SiNx: H increases.
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