Surface-plasmon-mediated emission enhancement from Ag-capped ZnO thin films

Ag/ZnO bilayer thin films are fabricated on Si substrates via two-step approach of ZnO sputtering + Ag evaporation. The enhancement of the near band edge (NBE) emission of the ZnO film is realized through coupling between the surface plasmon resonating energy at Ag/ZnO interface and the photonic energy of ZnO NBE emission. The dependence of the emission enhancement ratio of ZnO on the thickness and the growth temperature T of Ag cap-layers are investigated. By evaporating Ag(8 nm) cap-layer onto ZnO(100 nm) film at high substrate temperatures (T300 ℃), the value reaches about 18,i.e., 18, which is more than twice that of Ag(8 nm)/ZnO(100 nm) bilayer films grown at low temperatures (T200 ℃). It is found that the realization of the larger can be ascribed to the bigger surface roughness of Ag/ZnO bilayer samples prepared under higher growth temperatures.