Interface effects/heterojunctions and their applications

Abstract

The study of optical properties of heterostructure of zinc oxide and gold nanoparticles (ZnO/Au) was conducted elaborately to explore the interface effect of metal-semiconductor heterostructure/heterojunction towards its versatile potential applications. Atomic layer deposition grown ZnO was utilized to develop the coating on pre-synthesized Au-NPs templates. The reference systems, such as simultaneously grown ZnO thin-film and the template of Au NPs were studied to understand and get more insight into the heterostructure, ZnO/Au system. Metal nanoparticles has attracted a lot of attention from the research community because of their several novel properties including the unique properties like surface plasmon resonance (SPR). In this work the unique surface plasmon features of Au-NPs have been taken into account in designing the optical properties of the heterostructure. Whereas, the importance of optical properties of zinc oxide (ZnO), a direct bandgap II IV semiconductor with a large bandgap of about 3.37 eV and a binding energy of about 60 meV, is well known, and thus considered in our study of heterostructure system. The UV-Vis spectroscopic studies of ZnO/Au heterostructure and the reference system, the ZnO thin-film, were conducted to obtain the bandgap and the Urbach energy of the systems. The PL measurements revealed the presence of free exciton emission (FX) and its phonon replica (FX-2LO), both of which contributed to the near band emission. Distinct defect level emission (DLE) corresponding to oxygen vacancies was also observed for the reference ZnO system. The UV-Vis study of Au NPs revealed the presence of surface plasmon resonance and the PL measurement showed three distinct peaks at about 3.1 eV (due to the electronic transition from the higher hybrid orbitals to the d-band), ~ 2.4 eV (due to the electronic transition from the fermi level to the d-band) and at ~1.8 eV (due to the electronic transition from sp-band to the lower hybrid orbitals).