P-type nitrogen-doped β-Ga₂O₃: the role of stable shallow acceptor N_O-V_Ga complexes

In-depth understanding of the acceptor states and origins of p-type conductivity is essential and critical to overcome the great challenge for the p-type doping of ultrawide-bandgap oxide semiconductors. In this study we find that stable N_O-V_Ga complexes can be formed with ϵ(0/−) transition levels significantly smaller than those of the isolated N_O and V_Ga defects using N₂ as the dopant source. Due to the defect-induced crystal-field splitting of the p orbitals of Ga, O and N atoms, and the Coulomb binding between N_O(II) and V_Ga(I), an a′ doublet state at 1.43 eV and an a′′ singlet state at 0.22 eV above the valence band maximum (VBM) are formed for the β-Ga₂O₃:N_O(II)-V_Ga(I) complexes with an activated hole concentration of 8.5 × 10¹⁷ cm⁻³ at the VBM, indicating the formation of a shallow acceptor level and the feasibility to obtain p-type conductivity in β-Ga₂O₃ even when using N₂ as the dopant source. Considering the transition from N_O(II)-V⁰_Ga(I) + e to N_O(II)-V⁻_Ga(I), an emission peak at 385 nm with a Franck-Condon shift of 1.08 eV is predicted. These findings are of general scientific significance as well as technological application significance for p-type doping of ultrawide-bandgap oxide semiconductors.