Spectroscopic investigation of SnS quantum dots and the design of SnS QD- TiO₂ heterojunction

Abstract This work demonstrates the fabrication of p -type SnS quantum dots (QDs) and their hetero-junction with n -type TiO 2 . SnS QDs were prepared by colloidal synthesis process and were characterised by HRTEM, XRD and FTIR, which confirm the formation of SnS QDs with an average size of ∼2 nm. The density of states (DOS) distribution studied by scanning tunnelling spectroscopy (STS) shows the Dirac delta function type feature, confirming 0-D morphology. Further, the position of the Fermi level in DOS indicates p -type nature that is also supported by electron spin resonance (ESR) spectroscopy. The observed band gap from DOS is around 1.84 eV, which is also confirmed by photoluminescence spectra. A higher band gap value of these nanoparticles compared to that of bulk SnS (1.3 eV) indicates quantum confinement effect. To study the effect of QDs on heterojunction operation, SnS QDs were coated by the spray pyrolysis method on a compact TiO 2 layer-coated conductive glass substrate. Mott Schottky plot confirms the formation of a p–n junction. The complete band diagram, drawn by the help of J-V characteristics and STS results shows a type-II heterojunction. The band alignment information will help to analyse the transport of charge carriers in a SnS/TiO 2 heterojunction-based device.