Silver thick-film contacts on highly doped n-type silicon emitters: Structural and electronic properties of the interface

The properties of Ag thick-film contacts screen-printed on P-diffused [100] Si wafers have been investigated. In cross-sectional transmission electron microscopy, the interface is found to be composed of 200–500-nm-diameter Ag crystallites penetrating the silicon on average by up to 130 nm. The smaller crystallites are in epitaxial relation with the Si substrate, indicating their growth from the glass frit melt. A quasicontinuous glassy layer is present between the interface Ag crystallites and the larger Ag grains, which form the bulk of the contact. Conductive atomic force microscopy of cross sections shows that the interface crystallites form a low contact resistivity with the Si emitter in the range of 10−7 Ω cm2. We discuss the mechanisms of contact formation and propose a model in which the current flow from the emitter into the contact is not uniform, but occurs via a few isolated Ag crystallites that are directly connected or in close distance to the Ag grains forming the contact bulk.