Theoretical Interpretations of Sb Incorporation in GaN

Dilute concentrations of Sb doping in GaN induce large band gap-bowing and tunable photoluminescence (PL) at room temperature from the UV to the green spectral regions. However, the incorporation of Sb into the host nitride material, both within the bulk and on the surface, remains unclear. Previous work found that Sb is preferentially incorporated as an anion (Sb^3–) into the N sublattice. Here, we use first-principles calculations to explore the possibility that Sb may also be incorporated as a cation (Sb³⁺, Sb⁵⁺) into the metal sublattices. Our bulk defect thermodynamic analysis finds that Sb_Ga is energetically preferable compared to Sb_N under both N-rich and Ga-rich conditions in n-type samples. We next explore surface defect thermodynamics and quantify the site-selectivity of Sb incorporation for different crystallographic orientations. Our calculated band structures suggest the simultaneous presence of Sb^3- and Sb⁵⁺. Our calculated phonon spectra of Sb in different charge states successfully explain the origin of the experimentally observed additional Raman peaks of Sb-doped GaN. Our current results could be extended to other group-V dopants in GaN such as As, P, or Bi.