Dopant Concentration Imaging in Crystalline Silicon Wafers by Band-To-Band Photoluminescence

This paper introduces two photoluminescence-based techniques for imaging the dopant concentration in silicon wafers. Monitoring the band-to-band photoluminescence intensity is a highly sensitive method for excess carrier lifetime measurement. Such measurements are unaffected by various experimental artefacts caused by minority carrier trapping and depletion region modulation at low injection. The first technique is based on measuring the formation rate of iron-acceptor pairs, monitored by band-to-band photoluminescence in low injection. This calibration-free method provides accurate acceptor concentration images on p-type wafers, even if compensating dopants such as phosphorus are present. The second technique is based on photoluminescence images of unpassivated wafers, where the excess carrier concentration is pinned by a high surface recombination rate. This rapid technique is applicable to either p- or n-type wafers, creating high resolution images of the net doping density.