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.