Establishing Doping Limits for ZnGa₂O₄ for Ultrawide-Band-Gap Semiconductor Applications

ZnGa₂O₄ is an ultrawide-band-gap oxide with promising applications as a transparent conductor and a deep-UV electronic material. Despite this, their transport and doping limits remain poorly defined. Here, we present a comprehensive computational study combining hybrid density functional theory, density functional perturbation theory, and advanced transport modeling. We show that ZnGa₂O₄ exhibits a dispersive conduction band minimum with a low effective mass (0.27 m₀), supporting phonon-limited electron mobilities approaching 500 cm² V^-1 s^-1. However, impurity scattering dominates across experimentally relevant carrier concentrations, limiting the achievable mobility to values consistent with state-of-the-art measurements. Temperature-dependent band gap renormalization due to electron-phonon coupling is quantified and found to be strongly asymmetric between the conduction and valence bands, an effect that is essential to reproduce experimentally observed intrinsic carrier concentrations (∼9 × 10¹⁹ cm^-3). Defect calculations reveal that Ga/Zn antisites pin the Fermi level, driving degenerate n-type conductivity under typical growth conditions, while a p-type behavior is unlikely due to deep acceptor levels and polaron formation. Screening of extrinsic dopants demonstrates limited potential for further carrier enhancement, with most substitutions yielding high formation energies or deep traps. These findings establish the intrinsic and extrinsic doping limits of ZnGa₂O₄, highlighting both its potential as a deep-UV transparent conductor and the challenges for further performance optimization.