Conduction in amorphous thin films of silicon nitride under non-uniform electric fields

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Abstract
It is observed that amorphous thin films of silicon nitride with dissimilar (aluminium and silicon) electrodes exhibit conduction properties with a consistent dependence on the polarity of the applied electric field and the film thickness. In particular, for a given average field (voltage/thickness) it is found that: (i) conduction is larger for (aluminium) negative than for positive polarity; (ii) this effect is more pronounced with 500 Å films than with 1000 Å films; and (iii) for both polarities, conduction is larger for the 500 Å than for the 1000 Å films. This is surprising in view of the evidence in this paper that conduction in these films is by a bulk-controlled process. A model based on unequal trapping near the two electrodes, which creates a variation in the electric field with position into the film, is in qualitative agreement with all of the experimental results.