Electropassivation of silicon and bulk lifetime determination with dry polymer contact

Abstract

A new method for the determination of the bulk lifetime of minority carriers in silicon is presented. By applying a dry polymer (poly-epichlorhydrin-co-ethyleneoxide-co-allyl-glycylether with iodide/iodine) to silicon and exerting a negative potential to the silicon, an increase of the lifetime of photogenerated charge carriers (from 25 to 92 µs), measured by microwave conductivity techniques, is observed. This effect is caused by the electric field, which pulls minority carriers into the interior of the silicon wafer so that surface recombination can only continue on the back contact of the wafer. It is shown how, from this electropassivation effect, the bulk lifetime of silicon (0.81 ms in this case) and the effective diffusion constant can be obtained. Space-resolved images of minority carrier lifetimes show that it is difficult to get a homogeneous polymer-silicon contact at the whole wafer surface. Minority carrier lifetime against potential curves show that only polished silicon surfaces can be perfectly electropassivated. The procedure presented has potential for development as a technique for wafer characterization.