Dependence of effective carrier lifetime in iron-doped silicon crystals on the carrier injection level

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Abstract
The effective carrier lifetimes of oxidized silicon crystals have been studied using a microwave photoconductive decay method. The effective carrier lifetimes of the p-type samples, which had surface inversion layers, increased when the injected carrier concentrations were reduced, then converged towards the same saturated value although the samples had different bulk carrier lifetimes. The convergent value of the effective carrier lifetimes was found to be determined by the interface trap density. The effective carrier lifetimes of the n-type samples, which had surface accumulation layers, did not change with the injected carrier concentration. This study shows that very low carrier injection conditions give rise to the risk of wrong conclusions, depending on the silicon surface conditions, when the microwave photoconductive decay method is used to determine if bulk carrier lifetime degradation has been caused by contamination.
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