The origin of channel currents associated with P+regions in silicon

The mechanism by which very large channel currents can result in P⁺N junctions or in PNP transistors having annular P⁺diffused channel-stop regions was studied in detail using experimental structures whose oxides were intentionally contaminated with sodium ions. It is shown that the onset of channel current flow corresponds quantitatively to the formation of an inversion layer over the P⁺region. Possible mechanisms by which carriers can be supplied to the inversion layer, thereby resulting in a channel current, are considered. It is demonstrated that the mechanism involves the breakdown of the field-induced junction formed between the inversion layer and the underlying P⁺region. The breakdown characteristics of this field-induced junction are considered experimentally in detail. It is shown that breakdown can proceed through either a tunneling or an avalanche mechanism depending on the surface concentration of the P⁺region, and that the breakdown characteristics of field-induced junctions are much like those of narrow alloyed silicon junctions studied earlier by Chynoweth et al.