Influence of In-doping on microstructure, optical and electrical properties of sol-gel derived CdO thin films

摘要

Cadmium oxide thin films have been prepared on glass substrates by the sol–gel (SG) spin-coating technique. The structural, optical and electrical properties of the prepared films were studied as a function of the thicknesses. The results show that the optimum thickness for preparation of CdO films with high optical transparency and low resistivity is 211 nm. By using this optimized thicknesses and the same experimental conditions, transparent indium-doped cadmium oxide (In–CdO) thin films were deposited and annealed at 450 °C. Transparent and conducting In–CdO thin films for various concentrations of indium (1, 3 and 5 wt%), were prepared using the SG method. The electrical, optical and structural properties of these In–CdO films were investigated using different techniques, such as Hall measurements, optical transmission and X-ray diffraction (XRD). XRD patterns show that the films are polycrystalline. The structural analysis shows that all the samples have a cubic structure. Field emission scanning electron microscopy analysis reveals that the average grain size and surface morphology of CdO films are effectively changed by various In-doping concentrations. A minimum resistivity of 0.51 × 10_(−3) Ω cm and carrier concentration of 5.43 × 10_(20) cm_(−3)with high transmittance ~ 80% in the range 350–800 nm were achieved for 3 wt% indium doping. The band gap value starts at 2.32 eV for the undoped film and increases with doping concentration reaching the value of 3.07 eV for 5 wt% indium doping.