Asymmetric plasmon structures on ZnO: Ga for high sensitivity in the infrared range

This paper presents surface plasmons (SPs) on ZnO: Ga layers using an asymmetric insulator-metal-insulator (IMI) geometry. The water-ZnO: Ga-cytop tri-layers comprising IMI structures showed narrower surface plasmon resonance spectra than insulator-metal structures with water-ZnO: Ga single layers. Measurements of bulk sensitivities based on refractive index changes revealed extended evanescent fields on the ZnO: Ga layer surfaces when using reduced layer thicknesses. Consequently, the asymmetric IMI geometry on ZnO: Ga provides enhanced sensitivity in the infrared range. This result is further discussed from theoretical analyses of SP field distributions. This IMI geometry provides structural concepts to assist with developments in the area of oxide-based sensing applications.