Low-energy Ga₂O₃ polymorphs with low electron effective masses

We predict three Ga₂O₃ polymorphs with P2₁/c or Pnma symmetry. The formation energies of P2₁/c Ga₂O₃, Pnma-I Ga₂O₃, and Pnma-II Ga₂O₃ are 57 meV per atom, 51 meV per atom, and 23 meV per atom higher than that of β-Ga₂O₃, respectively. All the polymorphs are shown to be dynamically and mechanically stable. P2₁/c Ga₂O₃ is a quasi-direct wide band gap semiconductor (3.83 eV), while Pnma-I Ga₂O₃ and Pnma-II Ga₂O₃ are direct wide band gap semiconductors (3.60 eV and 3.70 eV, respectively). Simulated X-ray diffraction patterns are provided for experimental confirmation of the predicted structures. The polymorphs turn out to provide low electron effective masses, which is of great benefit to high-power electronic devices.