We investigate the structural and vibrational properties of Si:P thin films obtained by coevaporation of Si and P in ultra-high vacuum at room temperature followed by rapid thermal annealing. The thermal crystallization of the films was followed by Raman spectroscopy.Annealing at temperatures larger than 950 °C leads to the formation of crystalline phases.Density functional theory calculations of the vibrational modes allow us to identify orthorhombic SiP. Electron energy loss spectroscopy combined with energy dispersive spectroscopy give evidence of a plasmon signature of the SiP phase. The distribution of the crystalline phases in the film was imaged by energy filtered transmission electron microscopy.Both Si and SiP areas having sizes of a few microns are found to coexist in the films. Highresolution scanning transmission imaging provides a clear evidence of the lamellar structure while spatially resolved electron energy loss spectroscopy allows us to obtain a chemical mapping for both Si and P atoms, which agrees quite well with the orthorhombic structure of SiP. Our results represent an important first step on the way to obtain 2D SiP, a promising new material for which a direct bandgap has been predicted.

As building blocks of multifunctional materials involving coupling at the nanoscale, highly doped semiconductor nanocrystals are of great interest for potential applications in nanophotonics. In this work, we investigate the plasmonic properties of highly doped Si nanocrystals embedded in a silica matrix. These materials are obtained by evaporation of heavily phosphorus-doped SiO/SiO2 multilayers in an ultrahigh vacuum chamber followed by rapid thermal annealing. For P contents between 0.7 and 1.9 atom %, structural investigations at the nanoscale give clear evidence that P atoms are mainly located in the core of Si nanocrystals with concentrations reaching up to 10 atom %, i.e., well beyond the solid solubility limit of P in bulk Si. Alloying and formation of SiP nanoparticles are observed for P contents exceeding 4 atom % in the multilayer. Infrared absorption measurements give evidence of a localized surface plasmon resonance located in the 3–6 μm range. A core–shell structure was used to model Si nanocrystals embedded in a silica matrix. Based on the Mie theory and the Drude model, both the mobility and the free charge carrier density were extracted from the simulation, with values reaching 27 cm2 V–1 s–1 and 2.3 × 1020 cm–3, respectively. This results in a dopant activation rate of about 8%.