Electrical and optical properties of molybdenum-doped ZnO transparent conductive thin films prepared by dc reactive magnetron sputtering

Molybdenum-doped ZnO (ZMO) transparent conductive thin films were prepared by dc reactive magnetron sputtering on glass substrates from metallic targets. The structure, surface morphology, chemical state, optical and electrical properties of ZMO films were studied. The XRD pattern confirmed that ZMO thin films were polycrystalline with the hexagonal crystal structure, and the surface morphology measured by AFM demonstrated that the surface was smooth and compact. Chemical state analysis revealed that molybdenum atoms existed mainly in Mo6+ and Mo5+ ions but not in only single oxidation states. The minimum resistivity of 7.9 × 10−4 Ω cm is obtained with a carrier mobility of 27.3 cm2 V−1 s−1 and a carrier concentration of 3.1 × 1020 cm−3, and the average transmittance is more than 85% in the visible light region. The refractive index and extinction coefficient at the wavelength of 550 nm are 1.853 and 7.0 × 10−3, respectively. The energy bands increase from 3.37 eV to 3.8 eV with the increase in carrier concentrations and the carrier effective mass m* is 0.33 times the electron mass.