A significant enhancement in visible-light photodetection properties of chemical spray pyrolysis fabricated CdS thin films by novel Eu doping concentrations

This work deals with the preparation of undoped and rare earth europium-doped cadmium sulfide (Eu:CdS) films by spray pyrolysis procedure. X-ray diffraction (XRD), field emission-scanning electron microscopy, energy dispersive X-ray spectroscopy, ultraviolet-visible spectroscopy and photo-electrical studies were used to analyze the properties of the films. XRD analysis of CdS films showed polycrystalline nature with most preferred orientation along (002) and (101) for Eu:CdS. Eu doping improved the optical properties, the optical band gap of Eu:CdS films is noted to be larger compare to pure CdS thin films. Optical studies reveal the direct band gap variation from 2.43 eV to 2.48 eV with rising Eu doping from 1 wt.% to 5 wt.%. The increase in the nonlinear optical parameter was observed on Eu doping in CdS. The photo-electrical studies done for Eu:CdS films indicates that Eu doping has noticeable influence on electrical properties. The responsitivity for pure was ∼0.0629 AW⁻¹ which increased to 0.614 AW⁻¹, when 5 wt.% Eu was doped. The external quantum efficiency was enriched ∼ 8 times for 5 wt.% Eu:CdS compared to pure. The rise and decay time of Eu:CdS photodetector and its ON/OFF ratio was studied which is noticed ∼10 times larger compared to pure CdS. The observed enhancement in photodetector properties, morphology, crystalline quality and optical properties are caused by Eu doping concentration and hence will be more applicable in optoelectronics.