Growth and properties of transparent conducting CuAlO2 single crystals by a flux self-removal method

We investigated the growth and properties of CuAlO2 single crystals grown by a flux self-removal method. In this method, the flux crept up the wall of an alumina crucible completely during the slow cooling process, leaving flux-free CuAlO2 crystals on the bottom of the crucible. The resulting CuAlO2 crystals had typical dimensions of 0.5–5 mm in the ab-plane and 10–300 μm along the c-axis. The crystals had a hexagonal structure with a=b=2.857(1) Å and c=16.939(2) Å. Their resistivity was anisotropic with a c-axis resistivity (ρc) about ∼17 times higher than the ab-plane resistivity (ρab). However, both ρab and ρc showed thermally activated behavior with the same activation energy of ∼0.6 eV. The CuAlO2 crystals had direct and indirect bandgaps of 3.40 eV and 2.22 eV, respectively.

► CuAlO2 single crystals were grown by a flux self-removal method.
► Flux-free CuAlO2 crystals were found at the bottom of the Al2O3 crucible.
► CuAlO2 crystals have in-plane dimensions of 0.5–5 mm and a thickness of 10–300 μm.
► ρab and ρc are highly anisotropic but have the same activation energy of ∼0.6 eV.
► CuAlO2 crystals have direct band gap of 3.40 eV and indirect band gap of 2.22 eV.