Infrared nanoplasmonic properties of hyperdoped embedded Si nanocrystals in the few electrons regime

TL;DR

This study investigates the infrared plasmonic properties of phosphorus-doped silicon nanocrystals embedded in silica, revealing plasmon support with as few as 10 free electrons and uncovering hybridization and scattering phenomena at the few-electron limit.

Contribution

It demonstrates the ability of embedded silicon nanocrystals to support localized surface plasmons with extremely low free electron counts, and uncovers hybridization effects unique to the nanocrystal environment.

Findings

LSPR observed with only about 10 free electrons per nanocrystal.

Hybridization between plasmon modes and silica phonons causes avoided crossing.

New scattering process identified at high dopant concentrations.

Abstract

Using Localized Surface Plasmon Resonance (LSPR) as an optical probe we demonstrate the presence of free carriers in phosphorus doped silicon nanocrystals (SiNCs) embedded in a silica matrix. In small SiNCs, with radius ranging from 2.6 to 5.5 nm, the infrared spectroscopy study coupled to numerical simulations allows us to determine the number of electrically active phosphorus atoms with a precision of a few atoms. We demonstrate that LSP resonances can be supported with only about 10 free electrons per nanocrystal, confirming theoretical predictions and probing the limit of the collective nature of plasmons. We reveal a phenomenon, unique to embedded nanocrystals, with the appearance of an avoided crossing behavior linked to the hybridization between the localized surface plasmon in the doped nanocrystals and the silica matrix phonon modes. Finally, a careful analysis of the scattering time dependence versus carrier density in the small size regime allows us to detect the appearance of a new scattering process at high dopant concentration.