Highly Sensitive Broadband Photodetector Based on PbI2-Passivated CdS:Mn Quantum Dots with a Spectrally Flat Response

Abstract

This paper has demonstrated the role of manganese (Mn) doping in cadmium sulfide (CdS) quantum dots (QDs) and their surface passivation for the fabrication of highly sensitive broadband photodetectors. These photodetectors have been fabricated in a p–n heterojunction geometry using the Mn-doped CdS (CdS:Mn) QDs with TiO2 nanoparticles. The thin film of CdS:Mn QDs has been passivated with lead iodide (PbI2) for faster charge transport and broadening of the spectral response of the device. Our detailed X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy indicate a partial PbS formation, which also causes spectral broadening. In addition, this passivation process enables us to enhance the photosensitivity of the device with a spectrally flat response of quantum efficiency throughout the visible range spectrum (350–700 nm). This work also demonstrated that the photosensitivity of the device gradually increases with Mn doping with a faster photoresponse. The highest detectivity of the device was obtained with 4% Mn-doped dots with a value of ∼3.9 × 1012 Jones under −0.5 V external bias with a photoresponse time of 0.2 s, indicating its very high detectivity with a fast response.