Aluminum gettering of iron in silicon as a problem of the ternary phase diagram

Deep level transient spectroscopy is used to study the segregation of Fe from crystalline Si to an Al:Si liquid at its surface, which is the basic mechanism of aluminum gettering used in silicon photovoltaics. The measured segregation coefficient is smaller than estimates from the binary Fe:Si and Al:Fe phase diagrams. This apparent discrepancy originates from the ternary character of the system where the solubility of Fe in Si in equilibrium with the Al-doped α-FeSi2 has to be taken as a reference. Our data suggest that this solubility exceeds that in the binary Fe:Si system by two orders of magnitude.