Low-energy Ga 2 O 3 polymorphs with low electron effective masses.

We predict three Ga 2 O 3 polymorphs with P 2 1 / c or Pnma symmetry. The formation energies of P 2 1 / c Ga 2 O 3 , Pnma -I Ga 2 O 3 , and Pnma -II Ga 2 O 3 are 57 meV per atom, 51 meV per atom, and 23 meV per atom higher than that of β-Ga 2 O 3 , respectively. All the polymorphs are shown to be dynamically and mechanically stable. P 2 1 / c Ga 2 O 3 is a quasi-direct wide band gap semiconductor (3.83 eV), while Pnma -I Ga 2 O 3 and Pnma -II Ga 2 O 3 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.