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

Abstract

In this study, the pure and Cu doped CdO thin films with various doping concentrations (0 to 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 thin films were, then, investigated. The films were characterized through X-ray diffraction (XRD), field emission scanning electron microscopy equipped with 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 only with cadmium oxide phase with the cubic face-centered crystal structure and the preferred orientations were along (111), (200), (220), (311), and (311) planes. 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 as Cu dopant increased, so, too, the optical bandgap. As the Cu doping concentration increased from 0 to 5 (at.%), the electrical resistivity and Seebeck coefficient were found to increase from 3.74⋅10− 4 to 8.77⋅10− 3 Ω.cm and 8.28⋅10− 6 to 2.52⋅10− 5 v/k (at 100 Co temperature difference), respectively; the carrier concentration and carrier mobility were also found to decrease from 3.24⋅1020 to 1.76⋅1020 cm− 3 and from 55.5 to 4.05 cm2/v.s, respectively. The Hall effect and thermoelectric studies revealed that the films exhibited an n-type conductivity.