Green synthesis of copper sulfide (CuS) nanostructures for heterojunction diode applications

Abstract

Copper sulfide (CuS) rod shaped nanostructures with an average length 8 to 10 nm are synthesized through green chemical route using biodegradable starch as a capping agent under a nitrogen environment. Owing to the presence of a large number of glucose units linked by glycosidic bonds, starch can cap copper sulfide (CuS) nanoparticles. The preparation of CuS under nitrogen atmosphere produces fine quality CuS nanostructures by minimizing oxidation. XRD pattern reveals pure hexagonal covellite type CuS nanostructure with prime diffraction planes along (101), (102), (103), (006), (008), and (110) directions. The lattice parameters estimated as a = 3.790 Å and c = 16.51 Å. HRTEM studies show a well distribution of CuS nanorods. It shows prominent d-value of 0.28 nm corresponding to (103) hexagonal plane of CuS. The optical absorption extended up to 364 nm which is fairly blue shifted over bulk owing to the quantum confinement brought by starch. The photoluminescence emission is observed at 525 nm. The I–V measurements in planar geometry exhibit the linearity that reveals the ohmic behavior of carrier transport in CuS nanostructures. CuS nanostructures have been successfully used as effective p-type layer to fabricate sandwiched heterojunction devices with zinc chalcogenides (ZnO/ZnS and ZnS/ZnO) core/shell nanocomposites. The p-CuS/n-(zinc chalcogenides) heterojunction devices show good diode characteristics with an increase of ideality factor that may be attributed to surface defects and inhomogeneity in the barrier height. The photodetector also exhibits promising characteristics in terms of responsivity and quantum efficiency which are significant corresponding to material properties.