Lifetime Mapping

WT-2000 lifetime scanner from Semilab

Measurement principle

Our WT-2000 lifetime scanner from Semilab measures the effective minority carrier lifetime on silicon wafers. It uses the microwave induced photoconductance decay method (µ-PCD). The technique is based on the time-dependent determination of the reflectivity of the sample for microwaves. Increasing the minority carrier density by a short laser pulse leads to an increase in reflectivity, which afterwards goes back to its equilibrium value while these excess minority carriers recombine. From the decay-curve of the reflectivity, the minority carrier lifetime can be extracted. This lifetime is typically in the order of microseconds or a few milliseconds for solar grade silicon.

The system uses a scanning head with approximately 1 mm spatial resolution to produce lifetime maps of whole wafers.