CHANGES IN THE POOLE-FRENKEL COEFFICIENT WITH CURRENT-INDUCED DEFECT BAND CONDUCTIVITY OF HYDROGENATED AMORPHOUS-SILICON NITRIDE

Current induced conductivity in metal-semiconductor-metal thin film di odes containing hydrogenated amorphous silicon-rich alloys is determin ed by the concentration of silicon dangling bond states generated by t he 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-Si-x:H with band gaps in the ranges 2.3 to 2.9 eV, we have measured the field dependence of the conductivity after s tressing for increasing times and defect densities. By using the relat ionship between defect concentration and conductivity we have been abl e to establish that the apparent Poole-Frenkel coefficient (beta(PF)) changes from beta(PF) to 1/2 beta(PF) in a gradual way as the number o f defects increase in a given material. Furthermore, in the transition region where beta(PF) changes from the classical to the anomalous val ue, beta(PF) is linearly dependent on total number of defects. (C) 199 8 Elsevier Science B.V. All rights reserved.