Electronic properties and stability of M₂O₃ (M = Al, Ga, In) and alloy (M_xGa_1-x)₂O₃ in α and β phases: A theoretical study

Ga₂O₃ is clearly emerging as an important wide band-gap semiconductor. Band-gap engineering is now highly demanded for expanding its applications. Alloying with the same group of metal oxides is a straightforward and effective way. In this work, by using hybrid density functional theory calculations, the structural, electronic properties, and phase stability of group IIIA (Al, Ga, In) metal oxides and their ternary alloys (M_xGa_1-x)₂O₃ (M = Al, In) in the corundum and monoclinic phases are systematically investigated. The lattice constants, elastic constants, modulus, formation energies, band-gaps, band-gap deformation potentials, band-edge alignments, band-gap bowing, and ternary alloy formation energies are obtained. The basic relations between the geometric structure and electronic properties are discussed. It is found that the cation ordered structure is the most stable alloy structure in the monoclinic phase, rather than the random alloy structure as is commonly thought. A phase stability diagram of the (M_xGa_1-x)₂O₃ alloys is established, showing that the stable phase of the alloy changes from the monoclinic phase to the corundum phase when the incorporation of Al₂O₃ (In₂O₃) is greater than 69% (76%). These results can be used to understand the relative experimental data and shed some light on the synthesis and device design efforts of Ga₂O₃.