Formation of Ag and Au Plasmonic Nanoparticles by Ion Implantation in Ga${}_2$O${}_3$ thin films

Abstract

Gallium oxide (Ga${}_2$O${}_3$) is a wide-bandgap semiconductor with exceptional electrical and optical properties, making it a promising material for optoelectronic and sensing applications. In this work, we demonstrate for the first time the formation of plasmonic silver (Ag) and gold (Au) nanoparticles embedded in Ga${}_2$O${}_3$ thin films via ion implantation. Ga${}_2$O${}_3$ films deposited by RF sputtering on sapphire substrates were implanted with Ag or Au ions at 150 keV and a nominal fluence of 5 $\times$ 10${}^{16}$ ions/cm${}^2$, followed by thermal annealing between 200 and 700 °C. Rutherford backscattering spectrometry (RBS) measurements revealed saturation effects during implantation, resulting in lower incorporated fluences, as well as out-diffusion with post-implantation annealing. Transmission electron microscopy confirmed the formation of metallic nanoparticles with a distribution consistent with the metal profiles measured by RBS. Optical absorption measurements showed a pronounced localized surface plasmon resonance (LSPR) band in the Ag-implanted films, visible even in the as-implanted state and red-shifting with increasing annealing temperature, while Au-implanted films exhibited a distinct LSPR peak only after annealing at $\ge$500 °C. The observed LSPR shifts with annealing are attributed primarily to changes in the Ga${}_2$O${}_3$ matrix rather than a change in nanoparticle size. These results establish ion implantation as a viable approach for integrating plasmonic nanostructures into Ga${}_2$O${}_3$.