Native point defects and low p-doping efficiency in Mg2(Si,Sn) solid solutions: A hybrid-density functional study

Abstract

We perform hybrid-density functional calculations to investigate the charged defect formation energy of native point defects in Mg2Si, Mg2Sn, and their solid solutions. The band gap correction by hybrid-density functional is found to be critical to determine the charged defect density in these materials. For Mg2Si, Mg interstitials are dominant and provide unintentional n-type conductivity. Additionally, as the Mg vacancies can dominate in Mg-poor Mg2Sn, p-type conductivity is possible for Mg2Sn. However, the existence of low formation energy defects such as MgSn1+ and IMg2+ in Mg2Sn and their diffusion can cause severe charge compensation of hole carriers resulting in low p-type doping efficiency and thermal degradation. Our results indicate that, in addition to the extrinsic doping strategy, alloying of Mg2Sn with Mg2Si under Mg-poor conditions would be necessary to enhance the p-type conductivity with less charge compensation.