SERS substrates of doped germanium nanowires decorated with silver nanoparticles

• The 3D composite of AgNPs/GeNWs strongly enhances the Raman signal compared to the 2D AgNPs array.
• The composites properties of AgNPs/GeNWs depend on the microstructure and doping element of the Ge nanowires.
• The nanostructure of AgNPs/PGeNWs significantly enhances the R6G Raman signal compared to AgNPs/BGeNWs.

The microstructure and SERS activity of Ag-decorated Ge nanowires (NWs) doped with boron (B) or phosphorous (P) were investigated. The silver nanoparticles (AgNPs) distribution observed for the both types of doped nanowires differed significantly, as well as before and after the annealing procedures. The deposited strong-packed nonspherical Ag nanoparticles favor the Raman surface enhancement compared to spherical nanoparticles distributed along the nanowires with a larger interparticle distances after annealing. The SERS activity of the 3D nanocomposites is also influenced by the initial shape and the diameter of the nanowires and by the surface effects. The strongest SERS signal of Rhodamine 6G (R6G) was registered for the sample doped with P before annealing. Unlike the 2D AgNPs array the thermal annealing at 300 °C for 1 h destroyed the Raman activity of the B-doped composites and reduced the Raman peak intensities of the P-doped one.