Characterization of the microstructure and the optical and electrical properties of the direct-current magnetron sputtered CuO films at different substrate temperatures

Single-phased monoclinic CuO films with direct energy gap were deposited on the clean glass substrates by direct-current magnetron sputtering method. Effect of substrate temperature was in particular studied on the microstructure, and the optical and electrical properties of the films. With increase in substrate temperature, the crystallization of the polycrystalline CuO films is enhanced and thus the CuO film at substrate temperature of 600 degrees C has a clear < 111 > preferred orientation. Substrate temperature has different effect on the stress along the crystal axis a, b, and c, indicating an anisotropic growth along different crystal axis. The absorption edge of the films in the vicinity of 1.88 eV first moves towards short wavelength direction and then towards long wavelength direction with substrate temperature, which can be explained by the quantum size effect of the crystallites. The conduction transition of the films from p to n type takes places at substrate temperature of 500 degrees C. The p-type conduction is attributed to the copper vacancies and interstice oxygen, while n-type conduction is to the oxygen vacancies and interstice copper. The CuO film deposited at high substrate temperature has a larger carrier concentration and a lower electrical resistivity.