The widths of the valence bands in the copper ͑I͒ delafossites CuGaO 2 , CuInO 2 , and CuScO 2 have been measured by O K-shell x-ray emission spectroscopy and are compared with previous experimental work on CuAlO 2 and CuCrO 2. In agreement with recent density-functional theory calculations it is found that the bandwidth decreases in the series CuAlO 2 Ͼ CuGaO 2 Ͼ CuInO 2 Ͼ CuScO 2. It is shown that states at the top of the valence band are of dominant Cu 3d z 2 atomic character but with significant mixing with O 2p states.

The electronic structure of the prototypical p-type transparent conducting oxide CuAlO 2 has been studied by O K and Cu L 3 shell x-ray absorption and emission and Al K␣ excited x-ray photoemission spectroscopy. The nonresonant O K shell emission is dominated by the O 2p partial density of states, while the Al K␣ excited valence photoemission and nonresonant Cu L 3 emission spectra are dominated by the Cu 3d partial density of states. All three techniques reveal mixing between O 2p and Cu 3d states. Cu L 3 emission spectra excited just above the L 3 threshold are dominated by inelastic scattering with 5.5 eV energy loss. This energy is shown to correspond to the separation between the dominant peaks in the filled and empty densities of states.