Influence of nitrogen incorporation on the density of gap states in amorphous hydrogenated silicon

We report on the creation of states at midgap by nitrogen incorporation in a-Si: H. The density of states at midgap N(Ef) has been determined by measuring space-charge-limited currents. The introduction of nitrogen leads to an increase in N(Ef) and, at the highest nitrogen contents, this increase depends on the fourth power of the nitrogen concentration. The results are explained in terms of the structure of SIN alloys and it is suggested that the extra states originate from Si dangling bonds.