First-principles density-functional theory calculations reveal significantly different behavior between group-IIIA and IIIB delafossites $\text{Cu}M{\text{O}}_2$. 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 ${\text{CuScO}}_2$ and it diminishes further for ${\text{CuYO}}_2$ and ${\text{CuLaO}}_2$. Also, whereas group IIIA prefers rhombohedral stacking, group IIIB stabilizes in hexagonal structures. We further find that ${\text{CuScO}}_2$ has the highest calculated fundamental band gap among all the delafossite oxides. In addition, ${\text{CuLaO}}_2$ 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.

• Received 3 March 2009

DOI:https://doi.org/10.1103/PhysRevB.80.035205