Emitter sheet resistance from photoluminescence images

This paper presents proof-of-concept data for a method of determining the emitter sheet resistance of a diffused wafer from a photoluminescence image (PLI). The method uses inhomogeneous illumination to cause lateral current flow within the emitter, allowing lateral resistance affects to be observed in the photoluminescence (PL) signal. Both computer modelling and experimental results show a simple relationship between the ratio of the maximum photoluminescence from the illuminated region over the minimum photoluminescence from the non-illuminated region, and the product of the emitter series resistance of a wafer and the illumination intensity. The proof-of-concept method utilises this simple relationship to determine the emitter sheet resistance of a wafer from several PL images taken at different illumination intensities.