Structural, linear and nonlinear optical properties of Cd1−xAlxS semiconductor nanostructures: Influence of film thickness

Abstract

The work presented here reports the thickness dependent structural, linear and nonlinear optical properties of nanostructured Al-doped CdS thin films. Thin films were prepared with two different thicknesses(≈0.5 µm and 1 µm) by employing a spray pyrolysis (SP) technique for different Al-doping levels (0, 1, 3, 5 and 10 wt%). Powder X-ray diffraction studies confirm the polycrystalline crystal structure. The Scherrer rule was used to determine the crystallite size which was found to decrease with increasing doping concentration. Field emission scanning electron microscopy images showed uniform grain size which was found to slightly decrease with an increase in thickness of the films. The optical energy band gap (Eg) of the films was found to decrease with an increase of film thickness. The nonlinear optical parameters (NLO) of the samples were measured from the Z-scan data under DPSS continuous wave laser excitation at 532 nm which shows strong two-photon absorption. The increase in film thickness with Al-doping concentration from 0 to 10 wt%, the NLO parameters such as β, n2and χ(3) were enhanced from 4.66 × 10−4 to 3.67 × 10−3 (cm W−1), 5.26 × 10−9 to 3.38 × 10−8 (cm2 W−1) and 4.03 × 10−7 to 1.98 × 10−6 (esu), respectively. These important results of NLO parameters are due to the increase of localized defect states on grain boundaries with the increase of film thickness and suggest that these films are promising material for photonic device applications.