Effect of Rotational Speed on Linear and Non-Linear Optical Properties of Sol-Gel Spin Coated Nanostructured CdS Thin Films

Abstract

Cadmium sulfide thin films have been prepared by sol-gel spin coating method on glass substrates at different rotational speeds. Glancing angle X-ray diffraction patterns of CdS thin films exhibit cubic phase with (1 1 1) as preferential orientation. The surface morphology of the CdS thin films was studied by atomic force microscope. The electrical resistivity of CdS thin films decreased from 5.66 × 10³ to 1.72 × 10³ Ω.cm with the increase of rotational speed from 1500 to 3000 rpm. The optical transmittance of CdS thin films increased because of reduction in film thickness with the increase of rotational speed. The optical band gap of CdS thin films decreased from 2.65 to 2.46 eV with the increase of rotational speed due to quantum confinement effect. The normal dispersion of refractive index for CdS thin films is described using Wemple-DiDomenico single-oscillator model. The optical dispersion parameters such as single-oscillator energy (E_o), the dispersion energy (E_d) and the static refractive index n_o were calculated. The Verdet coefficient (V) is determined based on the refractive index dispersion study. The first and third order nonlinear optical susceptibility (χ⁽¹⁾, χ⁽³⁾), nonlinear refractive index (n₂) are determined for CdS thin films.<div><br></div>