Structural, electrical and magnetic characterization of in-situ crystallized ZnO:Co thin films synthesized by reactive magnetron sputtering

Zn1-xCoxO (0 < x < 0.146) conductive thin films have been deposited by reactive magnetron sputtering of metallic Zn and Co targets at high pressure and temperature. The structural properties have been investigated by using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It has been observed that all as-deposited films are crystallized in pure hcp ZnO structure and neither traces of metallic nor oxide Co-rich clusters were detected. The average grain size estimated from full width at half maximum of XRD results varied between 65 and 83 nm. XPS analyses exhibit that Co ions are successfully entered into ZnO lattice as Co. The electrical properties including conductivity, carrier density and carrier mobility were determined by Hall effect measurements in a temperature range from 300 K to 475 K. The conductivity of the films decreases from sigma(300K) = 2.2 x 10(4) to 2.3 x 10(-1) Sm-1 as the Co content changes from 0 to 0.146. Magnetic measurements reveal the absence of ferromagnetism even at 3 K and a paramagnetic Curie-Weiss behavior associated to magnetic clusters. (C) 2015 Elsevier B.V. All rights reserved.