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

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 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, which can be explained by P clustering inside the SiNCs.

Heavily Doped Si Nanocrystals Formed in P-(SiO/SiO2) Multilayers: A Promising Route for Si-Based Infrared Plasmonics

“…In the latter work, this value is underestimated by the presence of inactive P atoms in the oxide shell, which gives rise to an activation efficiency of 34% after chemical etching of the oxide shell. The value reported here is further in good agreement with activation efficiency values between 3 and 5% determined for heavily P-doped Si-NCs embedded in SiO 2 . Moreover, the spectral width of the LSPR peak is rather narrow as compared to the values reported in the literature. , One reason is probably the narrow P concentration distribution of doped Si-NCs, as indicated in Figure c.…”

“…The value reported here is further in good agreement with activation efficiency values between 3 and 5% determined for heavily P-doped Si-NCs embedded in SiO 2 . 28 Moreover, the spectral width of the LSPR peak is rather narrow as compared to the values reported in the literature. 23,38 One reason is probably the narrow P concentration distribution of doped Si-NCs, as indicated in Figure 3c.…”

“…Moreover, in the case of a single layer of hyperdoped Si-NCs embedded in a silica matrix, the absorption remains weak. 28 In this paper, we report on a tunable LSPR from heavily Pdoped Si-NCs formed in P-doped (SiO/SiO 2 ) multilayers. The multilayer approach has been successfully applied to achieve highly luminescent and size-controlled Si-NCs.…”

“…In the case of free-standing Si-NCs, the plasmonic properties turned out to be sensitive to oxidation and, more generally, to the modification of the chemical environment, which could be detrimental to applications. Moreover, in the case of a single layer of hyperdoped Si-NCs embedded in a silica matrix, the absorption remains weak …”

“…Both the extinction coefficient as well as the electromagnetic field in and around any kind of nanostructure can be calculated precisely, thus enabling the control of light in and around tiny structures. Very recently, Zhang et al 28 reported the observation of LSPR in a single layer of hyperdoped Si-NCs, with characteristic sizes lower than 6 nm, prepared by low energy ion implantation in a silica matrix and rapid thermal annealing. They demonstrated that only a few electrons in a nanocrystal can give rise to LSPR.…”