Self-doping behavior and cation disorder in MgSnN2

Investigations on II-Sn-N-2 (II = Mg, Ca) have been started very recently compared to the intense research of Zn-IV-N-2 (IV = Si, Ge, Sn). In this work, we study the phase stability of MgSnN2 and ZnSnN2 in wurtzite and rocksalt phases by first principles calculations. The calculated phase diagram agrees with the experimental observation; i.e., MgSnN2 can form in the wurtzite and rocksalt phases while ZnSnN2 only crystallizes in the wurtzite phase. Due to the higher ionicity of Mg-N bonds compared to Sn-N bonds and Zn-N bonds, wurtzite-type MgSnN2 appears under Mg-rich conditions. The defect properties and doping behavior of MgSnN2 in the wurtzite phase are further investigated. We find that MgSnN2 exhibits self-doped n-type conductivity, and donor-type antisite defect Sn-Mg is the primary source of free electrons. The high possibility of forming the stoichiometry-preserving Mg-Sn + Sn-Mg defect complex leads to our study of cation disorder in MgSnN2 by using the cluster expansion method with first principles calculations. It is found that cation disorder in MgSnN2 induces a band-gap reduction because of a violation of the octet rule. The local disorder, namely, forming (4,0) or (0,4) tetrahedra, leads to an appreciable band-gap reduction and hinders the enhancement of the optical absorption.

Automated summary

This study investigates the phase stability, defect properties, and cation disorder of MgSnN2 and ZnSnN2 using first principles calculations. It is found that MgSnN2 can form in two different phases, while ZnSnN2 only crystallizes in one phase. MgSnN2 exhibits self-doped n-type conductivity, and the defect Sn-Mg is the primary source of free electrons. Cation disorder in MgSnN2 induces a reduction in the band gap due to violation of the octet rule.