The effect of copper doping on the structural, optical, and electrical properties of cadmium oxide thin films deposited by the spray pyrolysis technique

In this study, the pure and Cu-doped CdO thin films with different doping concentrations (0-5 at.%) were deposited on soda-lime glass substrates using the chemical spray pyrolysis technique. The effects of Cu doping on the structural, optical, and electrical properties of the thin films were then investigated. The films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy using an energy-dispersive X-ray analyzer (FESEM-EDX), atomic force microscopy (AFM), ultraviolet-visible spectroscopy, and electrical resistance; van der Pauw techniques were also used to measure the Hall effect. X-ray diffraction studies showed that the thin films were polycrystalline and had only the cadmium oxide phase with the cubic face-centered crystal structure. The analysis also showed peaks associated with planes (111), (200), (220), (311), and (311). The FE-SEM and AFM images also showed that with an increase in Cu doping levels, the grain size and surface roughness of the thin films decreased from 472 to 38 nm and from 163 to 54 nm, respectively. The expected element compositions were confirmed by EDX. The optical bandgap of the thin films ranged from 2.42 to 2.56 eV, and with increasing Cu doping, the optical bandgap also increased. With the increase of Cu doping concentration from 0 to 5 (at.%), the electrical resistivity and Seebeck coefficient increased from 3.74 x 10(-4) to 8.77 x 10(-3) ohm.cm and from 8.28 x 10(-6) to 2.52 x 10(-5) v/k (at 100 (oC) temperature difference), respectively; the carrier concentration and carrier mobility decreased from 3.24 x 10(20) to 1.76 x 10(20) cm(-3) and from 55.5 to 4.05 cm(2)/v.s, respectively. The Hall effect and thermoelectric studies showed that the films exhibited n-type conductivity.