Computational Study for Structures and Electronic Properties of (RhAl)₂O₃ and (RhGa)₂O₃ Alloys for Optimal p‐Type Heterostructures in Group‐III Sesquioxides

The structural stability and electronic properties of (RhAl) 2 O 3 and (RhGa) 2 O 3 alloys with both corundum (α) and monoclinic (β) structures are theoretically investigated based on density functional calculations. The calculations reveal that the stable structure of (RhAl) 2 O 3 and (RhGa) 2 O 3 alloys depends on Rh composition. More importantly, (Rh 0.54 Al 0.46 ) 2 O 3 alloy with α phase, whose in‐plane lattice constant becomes equal to that of α‐Ga 2 O 3 , is found to be stabilized compared to the alloy with monoclinic phase. On the other hand, (Rh 0.25 Al 0.75 ) 2 O 3 alloy with β phase is stabilized and its lattice constants match those of β‐(Al 0.5 Ga 0.5 ) 2 O 3 . The analysis of electronic structures also reveals that both valence and conduction bands of (RhAl) 2 O 3 alloys around the energy gap mainly consist of 4 d orbitals of Rh atoms, suggesting a possibility of p‐type conductivity. Furthermore, it is found that lattice‐matched (Rh 0.54 Al 0.46 ) 2 O 3 /Ga 2 O 3 heterostructure with α phase exhibits type‐II band offset while (Rh 0.25 Al 0.75 ) 2 O 3 /(Al 0.5 Ga 0.5 ) 2 O 3 heterostructure with β phase exhibits type‐I band offset. These findings provide insights for fabricating ideal heterostructures with p‐type conductivity using group‐III sesquioxides.