Structural, electrical, and optical properties of CoxNi1-xO films grown by metalorganic chemical vapor deposition

• Highly oriented CoxNi1−xO films were grown on Al2O3by APMOCVD.
• Up to x=0.17, the average transparency in visible range is maintained at 71%.
• The bandgap energy of CoxNi1−xO decreases with increasing Co composition.
• N-type conductivity is observed by Hall measurement in high Co composition samples.
• We discuss the role of Co in different ionization states related to conductivity.

Thin films of cobalt-nickel oxide (CoxNi1-xO, x=0.01, 0.02, 0.08, 0.17, 0.22, 0.35, 0.56, 0.72) were grown on Al2O3 substrate by atmospheric pressure metalorganic chemical vapor deposition (APMOCVD). The effect of the cobalt composition on the structural, morphological, optical, and electrical properties of the films was investigated. X-ray diffraction (XRD) analysis revealed that all of the films grew with a preferred orientation towards [1 1 1]NiO and a twinned structure. Cobalt was well dispersed in the NiO structure up to x=0.08. CoxNi1-xO alloys were formed from x=0.17 to x=0.22, while phase-separated NiO and CoxNi1−xO formed when x≥0.35. The bandgap of the CoxNi1−xO film was found to decrease with increasing cobalt composition. Four-point probe measurements showed that the resistivity of the film also decreased with increasing cobalt composition, reaching a minimum of 0.006 Ωcm. Hall measurements of the films revealed n-type conductivity. The correlation between the presence of cobalt in different ionization states and the observed decrease in resistivity as well as the type of conductivity in CoxNi1−xO is discussed.