Evaluation of strain field around SiC particle in poly-crystalline silicon

Cast poly-crystalline silicon is unexpectedly contaminated with a large amount of oxygen and carbon impurities. However, the effect of carbon impurity is ambiguity. Recently, we made clear carbon impurity is locally super-saturated near grain boundaries. This local super-saturation can induce the precipitation of SiC particle. In this study, we investigated the influence of SiC particle to solar cell property, especially focusing the effect of the band-gap shrinkage induced by strain field in silicon caused by SiC precipitates. The strain field was directly observed by micro-Raman spectroscopy. Moreover, the strain field could be reproduced by calculation based on Eshelby's theory assuming strain is mainly due to the difference of thermal expansion. The strain was 0.1-0.2 % by experiments and 0.03-0.07 % by the calculations. The compressive or tensile strain of 0.03-0.2 % decreases the band-gap by 25-36 meV, which is equivalent to the thermal excitation energy at room temperature. This band-gap shrinkage is too small to capture carriers.