Relationship between the nano-structure of GaN surfaces and SERS efficiency: Chasing hot-spots

This work reviews different types of surface structures formed on selectively etched GaN substrates for surface-enhanced Raman scattering (SERS) measurements. A one-to-one correlation between nano-structure and SEAS efficiency, represented by the enhancement factor (EF), is shown by comparing SEM images with maps of Raman intensity. In this way, the location of hot-spots (H-Ss) is disclosed, leading to the selection of an optimal technology for manufacturing efficient and uniform SEAS platforms. GaN platforms with nano-structures containing bunched pillars and pyramids covered with an Au-Ag plasmonic layer reproducibly show an EF of up to 10(6) for 4-mercaptobenzoic acid (pMBA) test molecules. Platforms with pits (inverted pyramids) yield an EF of one order of magnitude lower.