Changes in the Poole–Frenkel coefficient with current induced defect band conductivity of hydrogenated amorphous silicon nitride

Abstract

Current induced conductivity in metal–semiconductor–metal thin film diodes containing hydrogenated amorphous silicon-rich alloys is determined by the concentration of silicon dangling bond states generated by the energy released during hole-electron recombination. This mechanism enables a range of defect concentrations to be introduced and results in a change in conductivity as carriers move between charged states in a defect band. Using a-SiNx:H with band gaps in the ranges 2.3 to 2.9 eV, we have measured the field dependence of the conductivity after stressing for increasing times and defect densities. By using the relationship between defect concentration and conductivity we have been able to establish that the apparent Poole–Frenkel coefficient (βPF) changes from βPF to 1/2βPF in a gradual way as the number of defects increase in a given material. Furthermore, in the transition region where βPF changes from the classical to the anomalous value, βPF is linearly dependent on total number of defects.