Studies on Structural, Morphological and Optoelectrical Properties of Spray-Deposited Iron-Doped Cadmium Oxide Thin Films

Cadmium-based transparent conductive oxides have received much attention due to their exceptional carrier concentrations, almost metallic conductivities and simple rock salt-like crystal structure. In the present study, the effect of iron (Fe) doping on physicochemical and opto-electrical properties of spray-deposited cadmium oxide (CdO) thin film was studied by varying the doping concentration of Fe. The X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-Vis spectroscopy, photoluminescence (PL) study and electrical properties using the Hall effect in Van der Pauw configuration were used to study the different physicochemical and optoelectrical properties of Fe-doped CdO thin films. The XRD patterns studied for Fe:CdO films show a polycrystalline nature and the crystallite size increases with an increase in doping concentration. FE-SEM images show an interconnected chain structure. The thickness of the films increases with an increase in doping concentration of Fe, as more nucleation sites are available. A transmittance of 76% was recorded at 550 nm wavelength for 4 at% doped Fe:CdO films. The direct band gap increases from 2.62 eV to 2.83 eV as the Fe doping concentration increases from 1 at% to 4 at% Fe:CdO films and further decreases to 2.71 eV. The PL spectrum indicates two emission peaks at 434.19 nm and 539.61 nm significantly. The electrical measurements show that Fe doping concentration in CdO film increases, the sheet resistance decreases from 2.89 Ω-1 to 2.06 Ω-1, which is attributed to the increase in mobility of carriers. The maximum mobility of 94.26 cm2/Vs is obtained for 4 at% Fe:CdO thin film. The figure of merit (Φ), a factor significant for opto-electronic applications, was found to vary between 3.40 × 10-3 Ω-1 and 31.16 × 10-3 Ω-1 for Fe: CdO films.