Effect of Cr doping on the optical―electrical property of CuAlO2 thin films derived by chemical solution deposition

Cr-doped CuAlO2 thin films were deposited on sapphire substrates by chemical solution deposition. The polycrystalline phase structure of CuAl sub(1-x)Cr sub(x)O2 (x=0-0.015) thin films was confirmed using an X-ray diffractometer in grazing incidence mode. All specimens are phase-pure. Optical-electrical property measurements show that with increasing Cr amount, electrical resistivity decreases from x=0 to 0.01, followed by an increase of x=0.015. This implies that two mechanisms affecting conductivity coexist and compete with each other. The predominance of the mechanisms changes with the increase in the Cr content. The detailed investigation on the transmittance in the ultraviolet region suggests that Cr doping can modify the structure of the top of valence band (VB) because Cr 3d states contribute to VB. Finally, 1% Cr doping can realize the best optimization of optical-electrical property with respect to transparent conducting oxide thin films.