Local Measurements of Diffusion Length and Chemical Character of Metal Clusters in Multicrystalline Silicon
We present a comprehensive description of synchrotron-based analytical microprobe techniques used to locally measure the diffusion length and chemical character of metal clusters in multicrystalline silicon (mc-Si) solar cell material. The techniques discussed are (a) X-ray fluorescence microscopy, capable of determining the spatial distribution, elemental nature, size, morphology, and depth of metal-rich particles as small as 30 nm in diameter; (b) X-ray absorption microspectroscopy, capable of determining the chemical states of these metal-rich precipitates, (c) X-ray beam induced current (XBIC), which maps the minority carrier recombination activity, and (d) Spectrally-resolved XBIC, which maps the minority carrier diffusion length. Sensitivity limits, optimal synchrotron characteristics, and experimental flowcharts are discussed. These techniques have elucidated the nature and effects of metal-rich particles in mc-Si and the physical mechanisms limiting metal gettering from mc-Si, and have opened several promising new research directions.
B. Pichaud, A. Claverie, D. Alquier, H. Richter and M. Kittler
T. Buonassisi et al., "Local Measurements of Diffusion Length and Chemical Character of Metal Clusters in Multicrystalline Silicon", Solid State Phenomena, Vols. 108-109, pp. 577-584, 2005