p-Type Conductivity Mechanism and Element Doping Modification in Wurtzite GaN from First-Principles Calculations

In the third generation of semiconductor materials, hexagonal gallium nitride (w-GaN) is expected to be a candidate for p-type transparent conductive materials (p-TCMs) because of its wide band gap and dispersed valence band maximum characteristics. However, research on its p-type conductivity mechanism and element doping modification is insufficient. In this study, the electronic structure, transparency, and transport characteristics of w-GaN were analyzed in depth, which confirmed that its electronic structure was suitable for bipolar doping and its application potential as p-TCMs. Then, the effects of intrinsic point defects in w-GaN and external doping on electronic and optical properties are systematically investigated, and the feasibility of p-type doping is also investigated. The results show that the main intrinsic defect of w-GaN is n-type VN, but its deep transition energy level limits the improvement of n-type conductivity. The investigations and discussions via Zn, IA, and IIA element doping modifications in w-GaN indicate that in a N-rich environment, the doping of Zn, Li, and Na is relatively easy to achieve and does not compromise the optical transparency. These defects have shallow charge conversion energy levels that can effectively ionize and produce holes, thereby improving p-type conductivity. More excitingly, the defect concentration of NaGa can reach as high as 1018 cm–3 at room temperature, identifying it as the optimal acceptor dopant among those screened in this study. Our finding not only confirms the potential of Zn, Li, and Na as ideal p-type dopants for w-GaN but also provides an effective strategy for achieving high p-type conductivity for w-GaN.