Low-Loss and Tunable Localized Mid-Infrared Plasmons in Nanocrystals of Highly Degenerate InN

Abstract

Plasmonic response of free charges confined in nanostructures of plasmonic materials is a powerful means for manipulating the light-material interaction at the nanoscale and hence has influence on various relevant technologies. In particular, plasmonic materials responsive in the mid-infrared range are technologically important as the mid-infrared is home to the vibrational resonance of molecules and also thermal radiation of hot objects. However, the development of the field is practically challenged with the lack of low-loss materials supporting high quality plasmons in this range of the spectrum. Here, we demonstrate that degenerately doped InN nanocrystals (NCs) support tunable and low-loss plasmon resonance spanning the entire midwave infrared range. Modulating free-carrier concentration is achieved by engineering nitrogen-vacancy defects (InN, 0.017 < x < 0.085) in highly degenerate NCs using a nonequilibrium gas-phase growth process. Despite the significant reduction in the carrier mobility relative to intrinsic InN, the mobility in degenerate InN NCs (>60 cm/(V s)) remains considerably higher than the carrier mobility reported for other materials NCs such as doped metal oxides, chalcogenides, and noble metals. These findings demonstrate feasibility of controlled tuning of infrared plasmon resonances in a low-loss material of III-V compounds and open a gateway to further studies of these materials nanostructures for infrared plasmonic applications.

Broadband Tunable Mid-infrared Plasmon Resonances in Cadmium Oxide Nanocrystals Induced by Size-Dependent Nonstoichiometry

“…To realize the full potential of plasmonics, a renewed emphasis has been placed on the development of new materials. − Unlike traditional noble-metal-based plasmonic materials that have an invariable free-electron density, carrier concentration in doped semiconductors can be controlled synthetically to activate plasmonic behavior in the visible and the infrared regions of the electromagnetic spectrum. − Over the past decade, LSPR at visible and NIR wavelengths has been demonstrated for a variety of semiconductor NCs, ranging from metal chalcogenides, − phosphides, , nitrides to doped metal-oxides. − LSPR in the mid-infrared (MIR) range (3–10 μm), on the other hand, provides a unique set of potential applications distinct from shorter wavelengths. , For instance, the abundance of molecular vibrational modes makes MIR a spectral region appealing for sensing applications, which could benefit from enhanced light–matter interactions made possible by leveraging tightly confined LSPR modes . Moreover, MIR plasmonic NCs could enable performance enhancement of MIR optoelectronic devices such as lasers and photodetectors. , Despite these promises, broadband tunable MIR plasmonic NCs derived from a single host material remains very limited. − …”

Plasma-based processes for planar and 3D surface patterning of functional nanoparticles

“…Operating in a vacuum brings the advantage of efficient charging of NPs in plasma and preserving the charge over long distance from the plasma. The nucleation and growth of InN NPs inside the plasma have been discussed in our previous report (Askari et al 2018). We expect that a large percentage of the sputtered material are converted into NPs depending on the operating parameters.…”

“…The cathode consists of a cylindrical tube (inside diameter 5 mm and length 55 mm) made from the solid precursor material (e.g., Ag). The cylinder is installed in a water-cooled holder with electric and gas fittings (see SI document and our previous report (Askari et al 2018) for details of the experimental setup). The carrier gas (e.g., Ar) flows through the hollow cathode with a flow rate in the range of 60-80 sccm.…”

“…The simplicity of sputtering from a solid target provides access to a vast library of functional materials including metals, alloys, oxides, and nitrides. Our previous studies show that the method is highly flexible in terms of control over size, chemical composition, and optoelectronic properties of the NPs (Ekeroth et al 2018;Askari et al 2018;Pilch et al 2013;Gunnarsson et al 2015;Ekeroth et al 2019).…”

Road Map for Nanocrystal Based Infrared Photodetectors

“…Addressing such low energy with interband transitions is extremely challenging since the confinement energy needs to be so small that the required size of nanocrystals becomes incompatible with colloidal stability or monodispersity. Intraband (Park et al, 2018 ) and plasmonic transitions (Luther et al, 2011 ; Agrawal et al, 2017 ; Coughlan et al, 2017 ; Askari et al, 2018 ; Liu et al, 2018 ) (achieved at a higher doping level) in doped nanocrystals, see Figure 3C , are interesting for two reasons: (i) addressing long wavelengths from the MWIR to the THz range while keeping the colloidal stability of the material and (ii) because doping of nanocrystals might not be limited to toxic material.…”