First-principle calculation of the pressure-induced variation in the formation energy of iron defect in Si1−xGex alloy

We report on the systematic first-principle calculations of the formation volumes of a single Fe (neutral iron) in Si1−xGex at various Ge compositions (x = 4.7–20.3%). The formation volume was defined as the derivative of the Fe formation energy with respect to the pressure within 0–0.8 GPa. Interestingly, the formation volume was found to be equivalent to the difference between the volumes of the relaxed bulk and defective structures. The formation volume versus ‘x’ exhibited a nonlinear pattern with regions of Fe-induced volume contraction (within x 50%, i.e., Ge-rich region). These results explain the reported observation that Fe prefers Si-rich environment and that Ge does not favor to be a nearest neighbor to Fe.