Single Oscillator Analysis, Electronic Polarizability and Optoelectronic Properties of Spin Coated Cobalt Doped Zinc Oxide Thin Films

Abstract

The structural, optical, single oscillator analysis, electronic polarizability, and optoelectronic properties of Co:ZnO thin films prepared via sol-gel spin coating are reported. X-ray diffraction analysis revealed a hexagonal wurtzite crystal structure, with crystallite size increasing from15.9 (0 mol%) to 16.37 nm at 4 mol.% then decreased to 14.86 nm at 8 mol%, attributed to lattice distortion and micro-strain. Strain energy density increased with Co doping, reflecting enhanced lattice distortions. UV-vis spectroscopy reveals a decrease in the optical band gap from 3.72 eV for 0 mol% to 2.76 eV for 8 mol%, while the refractive index increased from 2.23 to 2.47 . The oscillator energy in the single oscillator analysis through the Wemple-DiDomenico model increases from 4.091 eV (0 mol%) to 6.909 eV (8 mol%), the dispersive energy rises from 1.156 to 38.154 eV, and the oscillator strength increases from 0.36 × 10⁻⁵ to 29.8 × 10⁻⁵. Electronic polarizability also increased from 2.26 × 10⁻²⁵ to 2.45 × 10⁻²⁵ cm³, thus reflecting increased polarization arising from structural and electronic changes. Optoelectronic properties like the charge carrier, concentration plasma frequency, relaxation time and optical mobility were also maximized at 6 mol% cobalt doping and decreased at 8 mol%. On the other hand, the optical resistivity decreased from 9.49 × 10⁻²¹ to 2.29 × 10⁻²² Ωm. These findings therefore reveal that Co doping enhances the optical and electronic properties of ZnO thin films, hence making them suitable for optoelectronic applications, including sensors, solar cells, and nonlinear optical devices.