Defect Physics of Ternary Semiconductor ZnGe P2 with a High Density of Anion-Cation Antisites: A First-Principles Study

Anion-cation antisite defects usually have low density in the group III-V (e.g., GaN) and II-IV-V2 (ZnGeN2, ZnSnP2) semiconductors, and thus, have not drawn enough attention in defect studies of ZnGeP2 since 1976. However, our first-principles calculations based on a hybrid functional show that the anion-cation antisite defects (GeP and PGe) can have very high density (1017-1018cm-3), making them the dominant defects in ZnGeP2. Their calculated photoluminescence (PL) spectra agree well with the 1.4 and 1.6 eV PL peaks observed experimentally, indicating that they may be the origin of defects, which challenges previous assumptions that the P vacancy (-) defect is responsible for the two PL peaks. Although the anion-cation antisites (GeP and PGe) and cation-cation antisites (GeZn and ZnGe) both have densities as high as 1017cm-3, ZnGeP2 suffers from serious donor-acceptor compensation, which results in a low carrier density (below 1010cm-3), and thus, poor electrical conductivity. These results explain the mysterious observation that ZnGeP2 crystals grown using different methods have a high defect density, but low carrier density and high resistivity, and also indicate that it is challenging to suppress the defect-induced optical absorption in the development of high-power ZnGeP2-based optical devices.