Influence of Cd-content on structural and optical dispersion characteristics of nanocrystalline Zn_1−xCd_xS (0 ⩽ x ⩽ 0.9) films

Highlights: • Highly uniform and good adhesion of nanocrystalline Zn_1−xCd_xS films were synthesized. • Small magnitude of optical electronegativity was calculated. • Third-order nonlinear optical susceptibility and molar polarizability were considered. - Abstract: Low cost dip coating technique was successfully used to deposit highly uniform and good adhesive nanocrystalline Zn_1−xCd_xS (0 ⩽ x ⩽ 0.9) thin films. The surface morphology and crystalline structural characteristics of Zn_1−xCd_xS were achieved by using atomic force microscopy (AFM) and transmission electron microscopy (TEM), respectively. Transmission spectra show red shifting of absorption edge as the Cd content increased. The optical constants were accurately determined by using reflectance and transmittance spectra. The effect of Cd-content on refractive index, extinction index and other optical dispersion parameters were also investigated. The dispersion of the refractive index was discussed in terms of single oscillator model. In addition, the ratio of free carrier concentration to its effective mass was estimated. The calculated value of oscillator energy E_o obeys the empirical relation (E_o ≈ 2 E_g), obtained from single oscillator model. Small magnitude of optical electronegativity (χ^∗) for Zn_1−xCd_xS (0 ⩽ x ⩽ 0.9) thin films and relatively high refractive index can be attributed to covalent nature, in agreement with β value, obtained from dispersion energy analysis. Moreover, molar polarizability and third-order nonlinear optical susceptibility were also considered