Anomalously enhanced Raman scattering from longitudinal optical phonons on Ag-nanoparticle-covered GaN and ZnO

The authors report experimental studies of surface-enhanced Raman scattering (SERS) of wurtzite-type GaN and ZnO crystalline samples covered with Ag-nanoparticles. The longitudinal optical phonons consistently exhibit unusually intense Raman enhancement in comparison with other phonons. The anomaly is interpreted by a proposed model based on a resonant Raman scattering process assisted by metal-induced gap states at the Ag/GaN and Ag/ZnO interfaces. This study suggests that SERS of lattice vibrations in inorganic semiconductors is sensitive to their propagation nature, providing a progressive perspective view on electron-mediated enhanced Raman scattering.