A temperature dependant crystal orientation transition of cadmium oxide films deposited by metal organic chemical vapour deposition

A series of polycrystalline cadmium oxide thin films was deposited over a narrow temperature range. Calculating the texture coefficients from the X-ray diffraction peaks highlighted a crystal transition from a preferred (111) orientation at temperatures below 310 °C to a randomly oriented thin film above 331 °C. A mechanism for pre-coating of the substrate surface with a thin film of metallic cadmium has been proposed and its likely influence on the crystal orientation transition. The transition takes place in the region of the melting point of cadmium 320.9 °C and it is suggested that the change from a solid to liquid of the metallic cadmium surface influences the nucleation of the CdO film. The (111) oriented films were highly conducting with the best electrical properties; R s =18.0 Ω/sq, n=1.23×10 20 cm 3 μ=60.0 cm 2/V s, and ρ=8.5×10 −04 Ω/cm being achieved for a 500 nm film deposited at 289 °C. The optical bandgap of all films was found to be 2.5 eV with the (111) oriented films yielding the higher transmittance in the visible region. ► Polycrystalline cadmium oxide films were deposited over a narrow temperature range. ► X-ray diffraction peaks highlighted a crystal orientation transition. ► A mechanism is proposed relating to the melting point of cadmium 320.9 °C. ► Electrical properties achieved R s =18.0 Ω/sq, μ=60.0 cm 2/V s. ► The (111) oriented films yielded high transmittance in the visible region.