Spatial composition and injection dependence of recombination in silicon power device structures

Abstract

Recombination in forward conducting silicon power devices has been investigated by measuring the distribution of radiative recombination, and supplementally, the stored chargeQ, extracted by rapid commutation. The "axial" radiation distribution, detected through a slit moving perpendicular to the junction interfaces of the test specimens, includes surface recombination according to quantitative expressions presented. The volume lifetime is determined from the axial radiation profile together with the distribution recorded in the lateral direction. The high-level lifetime in the base region of p+-s-n+structures, determined from the radiation technique, is much larger than that extrapolated from the effective lifetime,\tau_{eff} = Q/I(Icurrent), considering recombination in the emitter regions according to classical principles. Recombination in the emitter regions, determined as a function of the concentration in the base region at high injection levels, has a significant linear component, superposed on the normal (almost) square-law dependence. The source and the consequences of these components of emitter recombination are discussed. The results are shown typically for p+-s-n+rectifiers and thyristors with conventional low-gradient diffusion profiles, and those with p-emitter regions where an abrupt doping gradient in the otherwise normal diffused layer limits the effective base region.