Effect of Solubility, Distribution Coefficient, and Stable Precipitates in Solar Cell Grade Silicon

1 Effect of Solubility, Distribution Coefficient, and Stable Precipitates in Solar Cell Grade Silicon 

The assessed thermodynamic properties of liquid and solid Si-based solution can be directly applied to evaluate the influence of third element on the solubility of the main impurity in silicon melt. For example, the effect of the impurity element on the solubility of C in pure Si melt can be evaluated by the following equation  

Since the impurities in SoG-Si feedstock are normally multidimensional in nature, it is important to estimate the influence of other impurities on the distribution coefficient of one impurity in pure Si. A simple relation has been derived for the effects of secondary impurities, j, on the distribution coefficient of i in pure Si, if the Henry s activity coefficients, 7, are available  

Here 2k 0 and 3are, respectively, the distribution coefficient of i in Si-i binary and Si-i-j ternary systems. Calculated A values for different impurities in pure Si are shown in Fig. 13.23. Most of the common impurities in pure Si have a positive contribution to the impurity distribution coefficient, i.e., the appearance of secondary impurities will increase the distribution coefficient of the primary impurity in silicon. 

Single crystal silicon is one of the important fundamental materials for the modern photovoltaic industry. The Czochralski method of growing single crystal silicon is affected by the thermocapillary convection. Temperature and concentration gradients at the free surface of the melt give rise to surface tension-driven Marangoni flow, which can lead to crystal defects, if it is sufficiently large. 

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