Investigation of Surface Breakdown by Light Scanning

EXPERIMENTAL investigations of surface breakdown in planar p-n junctions utilizing the technique of photoscanning are reported. A reduction in device breakdown voltage upon illumination of small areas of the oxide layer close to the p-n junction has been observed. The results suggest conclusions about failure mechanisms in oxide covered silicon p-n junctions and possible methods to prevent them. A model is presented which describes the variation of the break-down voltage by dividing the space charge layer near the interface into two regions: an ionization region containing a high electric field, and a trapping region. It is assumed that the electrons generated by the illumination change the charge state of the traps in such a way that the electric field within the ionization region is increased. The nature of the traps is not known, but further investigations are planned to elucidate details of the model.