Spatially resolved lifetime measurements of silicon heterojunctions from the modulated photoluminescence technique

Lifetime measurements are widely used both in research and industry as material and passivation quality characterization tools for silicon solar cells. Some of them combine spatial resolution together with mapping ability, which provides attractive and valuable images that lead for instance to a quick determination of poor regions of a sample. Here, we focus on microwave photoconductance decay (µ-PCD) and band-to-band photoluminescence (PL) measurements performed either in static or in modulated mode. Results are obtained on n-type crystalline silicon wafers passivated with intrinsic and doped hydrogenated amorphous silicon thin layers deposited on both faces by PECVD. In a first step we compare the static PL signal mapping and the µ-PCD lifetime mapping. In a second step, the static PL signal is correlated to the effective carrier lifetime deduced from modulated PL measurements. This allows us to transform the static PL signal into an effective carrier lifetime, and thus to provide a PL carrier lifetime mapping that can be directly compared to that obtained from µ-PCD. The lifetime mappings obtained in this way from both techniques are discussed.