Large bandgap tuning in corundum Al2(O1−xSex)3

Abstract

Wide-gap oxide materials including gallium oxide and aluminium oxide have been attracting much interest due to their tremendous potential for application in power devices. In this work, a new III-oxide material utilizing chalcogen and oxygen mixing to form Al₂(O_1−xSe_x)₃ III-oxychalcogenides is explored and studied. First-principles density functional theory calculations using hybrid functionals were applied to investigate the effect of Se on the electronic and structural properties of corundum Al₂(O_1−xSe_x)₃ alloys. Analysis on formation enthalpies indicated that Al₂(O_1−xSe_x)₃ alloys exhibit a large miscibility gap, rendering a single-crystal or metastable phase achievable if the Se content remains 8% or less. Our investigations on electronic properties show that Se addition leads to a significant reduction of the bandgap energy of Al₂O₃, providing a remarkably large energy bandgap tuning range of 7.46 eV. In addition, band alignment studies reveal a type-I band offset for the Al₂(O_1−xSe_x)₃/Al₂O₃ structure across the entire composition range, in which the valence band offset to conduction band offset ratio reaches as high as 0.7 : 0.3 when the Se content is less than 6%. Interestingly, although adding Se leads to a significant upward movement of the valence band in Al₂(O_1−xSe_x)₃ alloys, the downward movement of the conduction band becomes dominant when the Se content increases. Overall, our work reveals the peculiar properties of mixed-anion AlOSe III-oxychalcogenides that show potential values for technological applications. More importantly, our initial work here carves out an uncharted territory in III-oxychalcogenides that requires further investigations from both experimental and theoretical approaches.