Schottky junction UV photodetector based on CdS and visible photodetector based on CdS:Cu quantum dots

Abstract

We report the synthesis of cadmium sulphide (CdS) quantum dots (QD), copper doped cadmium sulphide (CdS:Cu) quantum dots and silver (Ag) nanoparticles embedded in polyvinyl alcohol (PVA) and fabrication of nano CdS (undoped and doped)–Ag Schottky barrier. Chemical route is followed for CdS, CdS:Cu and Ag nanoparticles synthesis. Sizes and shapes of CdS and Ag nanoparticles are obtained from UV–vis, PL, XRD, SEM, TEM, HRTEM, SAED and composition from EDS. Nano scale devices are fabricated with ITO/TPD/CdS (undoped/doped) nanocomposites (NCs)/Ag nanoparticles/Al to study the Schottky barrier characteristics. Current–voltage (I–V) characteristics of the as-fabricated devices are performed under dark and light environment which show the Schottky barrier characteristic of the devices. The Schottky junctions exhibit rectifying behavior in the dark. The as-fabricated nano scale Schottky devices are found to be sensitive to light sources differing in wavelength. We have seen that the responsivity as well as external quantum efficiency (EQE) of the devices increases after doping. The photo response and EQE of the devices are found to increase with decrease in QD size. For CdS–Ag (undoped and doped) Schottky devices EQE is higher in the UV region, whereas responsivity is higher for CdS–Ag Schottky devices (undoped) in the UV region and for CdS–Ag Schottky devices (doped) in the visible region.