Investigation of low injection effects using the local ideality factor obtained from effective lifetime measurements

The effective minority carrier lifetime of p-type silicon wafers passivated by silicon nitride and of n-type silicon wafers passivated by aluminum oxide often decreases significantly as the excess carrier concentration decreases. Several theories have been postulated to explain this effect. The main ones are asymmetric carrier lifetimes, high recombination within a surface damage region, and edge recombination. As in some cases the effective lifetime measurements can be fitted quite well by all these effects, it is challenging to determine which of them limits the low injection performance of a specific wafer. This study demonstrates that although these mechanisms affect the lifetime in ways that are difficult to be distinguished, they have a significantly different influence on the resulting injection-dependent local ideality factor. It is therefore suggested that the injection dependent local ideality factor can be used to distinguish between these mechanisms.