Group-IIIA versus IIIB delafossites: Electronic structure study

First-principles density-functional theory calculations reveal significantly different behavior between group-IIIA and IIIB delafossites CuMO2. The group-IIIA delafossites have indirect band gaps with large differences between the direct and indirect band gaps. However, this difference is small for the group-IIIB delafossites: only 0.22 eV for CuScO2 and it diminishes further for CuYO2 and CuLaO2. Also, whereas group IIIA prefers rhombohedral stacking, group IIIB stabilizes in hexagonal structures. We further find that CuScO2 has the highest calculated fundamental band gap among all the delafossite oxides. In addition, CuLaO2 is found to have a direct band gap. These differences are explained by the different atomic configurations between the group-IIIA and IIIB elements. Our understanding of these delafossites provides general guidance for proper selection of delafossites for suitable applications in optoelectronic devices.