Determination of the bulk carrier lifetime in the low-doped region of a silicon power diode, by the method of open circuit voltage decay†

Abstract

The open-circuit voltage decay (OCVD) of excess carriers injected into the low-doped region of a P+LN+ diode during heavy forward bias, can give a direct measure of the effective carrier lifetime in this region. The complete transient solutions for the excess carrier density valid both for d.c. forward bias current flow and for the OCVD after abrupt cessation of the current, show that for a variety of boundary conditions—zero or finite recombination in the end regions (Davies 1963, Schlangenotto and Gerlach 1972), infinite surface recombination velocity at an ohmic contact (Choo and Mazur 1970)—the OCVD after an initial very rapid transient settles down to a simple decay, governed essentially by the bulk lifetime τB of the L-region or an effective lifetime τc respectively. The diodes investigated had π- or v-type L-regiona with their P—N junctions made by diffusion and their L—H junctions by alloying. Apart from an extremly rapid initial transient, the OCVD measured was linear and showed two regions of di...