Recombination activity of interstitial iron and other transition metal point defects in p- and n-type crystalline silicon

Interstitial iron in crystalline silicon has a much larger capture cross section for electrons than holes. According to the Shockley-Read-Hall model, the low-injection carrier lifetime in p-type silicon should therefore be much lower that in n-type silicon, while in high injection they should be equal. In this work we confirm this modeling using purposely iron-contaminated samples. A survey of other transition metal impurities in silicon reveals that those which tend to occupy interstitial sites at room temperature also have significantly larger capture cross sections for electrons. Since these are also the most probable metal point defects to occur during high temperature processing, using n-type wafers for devices such as solar cells may offer greater immunity to the effects of metal contaminants.