Doping Density in Silicon and Solar Cells Analyzed With Micrometer Resolution

A quantitative doping density mapping technique for silicon samples with micrometer spatial resolution is presented. Being based on confocal microphotoluminescence spectroscopy, the technique allows for detailed quantitative analyses on the doping concentration of microscopic technological structures in silicon solar cells. The confocal microscope setup enables laser illumination with micrometer-sized focus and fast low-noise detection of the emitted luminescent radiation which depends on doping and free excess carrier density. The doping density is determined by calibrating the depth-dependent luminescent radiation with results from 2-D simulations of the carrier density. The high-resolution method is demonstrated on a state-of-the-art doping structure for back contact solar cells, where small deviations in the doping homogeneity can be detected. This proves the potential of the proposed technique to enhance the processing of doping microstructures and to strengthen the understanding of their physical properties.