Metal-nitride layer with plasmonic optical structure
developed within TACR grant no. TH02020926
4“(four inch) sapphire wafer with microcrystalline GaN and silver nanocrystals, which exhibit plasmonic resonance in the visible part of the electromagnetic spectrum, close to UV. GaN preparation summary: 1. Gradual heating of sapphire wafer to T = 800 °C for 60 minutes, temperature stabilization, 2. Wafer cooling to nucleation temperature 650 °C, 3. Nucleation of the layer (3 min.), 4. Gradual heating to deposition temperature, 5. First part of GaN deposition from TMGa (trimethylgallium) and NH3 (ammonia) with gas flows of 50 sccm, resp. 3000 sccm; deposition pressure was 150 Torr, wafer temperature 810 °C and deposition time 30 min., 6. Second part of GaN deposition from TMGa (trimethylgallium) and NH3 (ammonia) with gas flows of 35 sccm, resp. 3600 sccm; deposition pressure was 120 Torr, wafer temperature 830 °C and deposition time 30 min, 7. Controlled cooling in ambient nitrogen for 60 min. As plasmonic structures silver colloids with diameters of 40 and 80 nm were used. For silver deposition the colloidal solution was modified by 3mM solution of HCl (to alter the Zeta potential of GaN) and the deposition took 15 minutes. Sample exhibits photoluminescence related to the band gap emission of GaN (3.4 eV/365 nm).
GaN layer is polycrystalline (top image), with medium density of larger crystals with well-defined facets (inset shows the wafer as a whole). Silver nanoparticles are deposited on the facets in different densities: high density (left), isolated single nanoparticles (middle) or as dimers (right), which allows to selectively inspect their effect on GaN PL..
The sample exhibits strong photoluminescence in expected spectral region for GaN and Ag nanocrystals (close UV), XRD analysis shows peaks confirming GaN in common crystallographic structure.