Nonthermal plasma synthesized silicon-silicon nitride core–shell nanocrystals with enhanced photoluminescence

Enhanced optical properties of silicon quantum dots (QDs) are pertinent for light-emitting applications including luminescent solar cell concentrators. Surface passivation plays a crucial role in improving photoluminescent quantum yield and effective carrier lifetimes of silicon nanocrystals and is often achieved by surface grafting of organic ligands. However, organically passivated silicon QDs often suffer from a deterioration of the optical properties when exposed to the environment. In this work, we explore the effect of an inorganic amorphous silicon nitride (SiN_x) shell on silicon QDs and their optical properties. Utilizing a dual plasma approach with dual injection ports, we synthesized Si/SiN_x core–shell nanoparticles using SiH₄, NH₃, H₂, and Ar. The core–shell nanocrystals were characterized using optical and structural methods, which revealed that higher nitridation plasma powers could lead to Si precipitation altering the composition of SiN_x shell. While as-synthesized Si/SiN_x core–shell nanocrystals did not exhibit photoluminescence, oxidized Si/SiN_x core–shell nanocrystals show significantly higher quantum yield (35%) and longer carrier lifetime compared to their bare oxidized Si analogues even after an environmental exposure of six months.