Influence of contact architecture on the high-field characteristics of planar silicon structures

The profile of the contact metallization is observed to play a significant role in the high-field behaviour of high-resistivity Si wafers used for photoconductive power switch applications. In this paper, we present the influence of five different contact geometries on the electric field distribution and leakage current variation in high-resistivity silicon wafers. Experimental results indicate that at high fields, current filamentation occurs due to local avalanche phenomena at high-stress locations when the field enhancement is concentrated in a narrow region forcing a high current density. The threshold for current filamentation is not solely determined by the magnitude of the field enhancement alone, but also the localization of the field enhancement in a narrow region and the consequent increase of current density in that localized region. The experimental results are supported by numerical field computations as well as by optical micrographs that confirm the occurrence of surface filamentation at concentrated high-stress locations. Based on the experimental and computational results, contact geometries suitable for high-field applications of planar Si structures is suggested and the maximum field up to which each geometry can be used without surface filamentation is compared.