Thermodynamics of phosphorus in molten silicon

Abstract

Removal of phosphorus is one of the major problems on the purification of molten silicon for solar cell. The Gibbs energy change of phosphorus dissolution into molten silicon was determined in the temperature range from 1723 to 1848 K by equilibrating a molten silicon-phosphorus alloy in a controlled phosphorus partial pressure and is expressed by the following equations.

$$\begin{gathered} \frac{1}{2}P_2 (g) = \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{P} (mass pct, in Si) \hfill \\ \Delta G^\circ = - 139,000{\text{ }}( \pm 2000){\text{ }} + {\text{ }}43.4{\text{ }}( \pm 10.1T){\text{ }}(J/mol) \hfill \\ \end{gathered} $$

The possibility of removing phosphorus from silicon melts by vacuum treatment and the accompanying yield of silicon during the refining process are discussed.