Micro-photoluminescence studies of shallow phosphorus diffusions below polysilicon passivating contacts

Micro-photoluminescence spectroscopy is applied in this work to characterise the shallow phosphorus diffusions occurring below poly-silicon passivating contacts for silicon solar cells, courtesy of the bandgap narrowing effect in the heavily-doped region. We present the photoluminescence spectra from samples of various diffusion profiles, achieved by changing the phosphorus diffusion temperature and oxide interlayer thickness. The photoluminescence peak from the shallow phosphorus diffusion region, when normalised against the substrate crystalline silicon peak, changes in intensity in accordance with the dopant profiles. Photoluminescence spectra measured with two lasers of different penetration depths are compared in this study, and their relative strengths and weaknesses are assessed. Micron-scale line scanning across localised poly-silicon structures demonstrates that the method can identify the presence of the underlying diffused regions with a spatial resolution of several microns.