Insight into Al doping effect on photodetector performance of CdS and CdS:Mg films prepared by self-controlled nebulizer spray technique

Visible light photodetector is one of the rapidly growing fields in optoelectronics. We report investigation of photoelectrical properties of visible lateral photodetectors based on pure CdS, Mg or Al doped CdS and Mg+Al co-doped CdS thin films prepared by the spray technique. The CdS phase purity was confirmed by X-ray diffraction and Raman studies. The morphological analysis shows spherical shaped grains in the pure CdS film. The nature of grains slightly changes from spherical to rod-like shape for the doped films, confirming the incorporation of doped ions into the host lattice. The prepared films exhibit bandgaps around 2.3 eV. The photodetector structures were illuminated by laser light with energy of 2.33 eV (532 nm). Under such an above-bandgap excitation, electron-hole pairs are created by the band-to-band absorption of photons, resulting in the enhancement of photocurrent. The fabricated photodetector is able to work at room temperature under very low excitation power density ranging 1–5 mW/cm². The Al doped CdS photodetector at 5 V bias exhibits the highest photocurrent of 1.06 × 10⁻⁵ A, responsivity (R) of 2.13 A/W, detectivity (D*) of 5.23 × 10¹¹ Jones and external quantum efficiency (EQE) of 497.3% under 532 nm illumination.