Effect of lattice constraint on structural stability and miscibility of (Al
 x
 Ga1-x
 )2O3 films: a first-principles study


 The structural stability and miscibility of (Al
 x
 Ga1-x
 )2O3 alloys are theoretically investigated by means of electronic structure calculations within density functional theory. Effect of lattice constraint due to α-Al2O3(0001) substrate and (Al0.4Ga0.6)2O3 buffer layer on the structural stability and miscibility are evaluated from the energy differences and the excess energies among α, β, and κ phases. For the constrained systems by α-Al2O3(0001) substrate, only α-phase (Al
 x
 Ga1-x
 )2O3 is found to be stabilized. Furthermore, the lattice constraint drastically improves the miscibility of (Al
 x
 Ga1-x
 )2O3 alloys. These results suggest that the lattice constraint is crucial for the stability and miscibility of (Al
 x
 Ga1-x
 )2O3 alloys.