Density Functional Study of Sn Solubility and Atomic Configuration in SiSn and GeSn Alloys

SiSn and GeSn semiconductors are attracting much attention for their application in electronic and optoelectronic devices. However, the fundamental understanding of material properties of Sn‐doped Si (Ge) alloys is still insufficient. To address this, we use density functional theory calculations to examine (1) the formation energy ( E f ) and the thermal equilibrium concentration ( C eq ) of Sn atoms in the bulk and near the (001) surface of Si (Ge) and (2) the stable configuration of Sn atoms in the bulk of Si (Ge). The important results in study (1) are that the C eq of substitutional Sn (Sn s ) atoms is determined as 8.08 × 10 22 exp(−0.671 eV/kT) cm −3 and 8.68 × 10 22 exp(−0.272 eV/kT) cm −3 for bulk Si and Ge, respectively. The reliable E f of interstitial Sn (Sn i ) atoms indicated that the Sn i is not incorporated into Si and Ge matrices during film growth. The important result in study (2) is that preferential sites of Sn s atoms in Si and Ge are determined up to 50% Sn composition. A new structure of Ge 0.5 Sn 0.5 is discovered that is more stable than a zinc blende structure. More metastable structures containing SnSn bonds exist in Si than in Ge at 37.5% and 50% Sn compositions.