Effect of Cobalt Doping on the Structural, Morphological, Optical, and Magnetic Properties of ZnO Thin Films Prepared by Ultrasonic Spray Pyrolysis

Zinc-cobalt oxide (Zn1−xCoxO) thin films refer to a semiconductor material based on zinc oxide (ZnO) doped with cobalt (Co). This material is studied mainly for its modified magnetic, electronic and optical properties, particularly in the context of diluted magnetic semiconductors (DMS). This study analyzes the effect of cobalt doping on the structural optical, and magnetic properties of ZnO thin films, fabricated using alow-cost, scalable ultrasonic spray technique. Zinc-cobalt oxide (Zn1−xCoxO) thin films were successfully deposited on glass substrates using the ultrasonic spray pyrolysis technique at a substrate tem- perature of 450 ◦C, with cobalt doping concentrations of x = 0%, 1%, 3%, and 5%. X-ray diffraction (XRD) analysis revealed a hexagonal wurtzite structure for all samples, with no secondary phases, indicating effective incorporation of Co2+ ions into the ZnO lattice. Raman spectroscopy indicated the emergence of structural disorder and defect-related modes, consistent with the increase in Urbach energy. Scanning electron microscopy (SEM) showed granular surface morphologies, and a non-homogeneous surface pattern is visible on all samples. Atomic Force Microscopy (AFM) showed an increase in surface roughness and grain size with increasing doping concentration. Optical measurements confirmed high transmittance in the visible range and a gradual de- crease in optical band gap from 3.21 eV to 2.95 eV with increasing Co content. The spectroscopy, and vibrating sample magnetometer (VSM) revealed that all films are intrinsically ferromagnetic. The origin of the ferromagnetism was found to be an intrinsic property of the Co-doped ZnO thin films.