A noticeable effect of thickness on third order nonlinear properties of CBD grown CdS thin films investigated by Z-scan measurements

Abstract

In current work, thin films of CdS with alike thickness were fabricated by chemical bath deposition by varying the deposition time. Thickness of films was measured to be ∼200, 250 and 300 nm using Alfa step stylus profilometer. As thickness play significant role hence thickness dependent structural, vibrational, morphological, optical and third order nonlinear optical (TONLO) studies are exclusively explored. The XRD and FT-Raman studies revealed an enhancement in crystallinity with increasing thickness of films and also confirmed non existence of any impurity peak. Crystallite size evaluated from Scherrer's rule is found to be increased from 21 to 30 nm with increasing the thickness of films. Scanning electron microscopy images demonstrates the modification of spherical nanoparticles to nano needles with increase of thickness of films. Average size of grains are intuited to be in 30–65 nm range. Transmission spectra showed high transparency for films of 200 nm thickness and later reduced with increase of thickness. Direct energy gap was attained in range of 2.2–2.3 eV. Stable values of k and n indicates defect free films. The n2 and χ3 values are found to very high which are in range of 3.15–8.67 (×10−6) and 1.11 to 1.47 (×10−1), respectively. Such transparent films with higher TONLO susceptibility values are potential candidates for optoelectronic device applications.