Bias Tunable Spectral Response of Nanocrystal Array in a Plasmonic Cavity

Abstract

Nanocrystals (NCs) have gained considerable attention for their broadly tunable absorption from the UV to the THz range. Nevertheless, their optical features suffer from a lack of tunability once integrated into optoelectronic devices. Here, we show that tunable absorption with bias can be obtained by coupling a HgTe NC array with a plasmonic resonator. Up to 15 meV blueshift can be achieved from a 3-µm absorbing wavelength structure under a 3 V bias voltage when the NC exciton is coupled with a mode of the resonator. We demonstrate that the blueshift arises from the interplay between hopping transport and inhomogeneous absorption due to the presence of the photonic structure. The observed tunable spectral response is qualitatively reproduced in simulation by introducing a bias-dependent diffusion length in the charge transport. This work expands the realm of existing NC-based devices and paves the way towards light modulators.

Nanocrystal-Based Active Photonics Device through Spatial Design of Light-Matter Coupling

“…Indeed, the bias applied to the photodetector modifies the value of the diffusion length, which in turn affects the spatial extent of the active region from which photoexcited carriers are collected. This gives rise to a device with reconfigurable response if the absorption of the NC film is inhomogeneous . In order to implement a spatially inhomogeneous absorption, the NC array is coupled to a grating resonator which has a dual role of collecting photoexcited carriers and generating multiple absorption resonances.…”

“…As the applied bias increases, the ratio between the intensity of the TE F–P resonance and the intensity of the GMR grows from 0.1 for a bias of 0.1 V to 0.44 for a bias of 1.5 V. Note that this spectral modulation is fully reversible (i.e., the peak intensity ratio decreases when the applied bias decreases) and is not dependent on the bias polarity. Here, the Stark effect can be excluded as a possible mechanism to explain the origin of this bias reconfigurability since it requires an electric field above 100 kV cm –1 to generate a much smaller band edge shift, , also see Figure S20. Moreover, the Stark effect will affect both polarizations the same way.…”

“…The resulting thin films are thus poorly photoresponsive, and light management strategies have to be introduced to absorb a significant part of the incident light into a NC slab whose size matches the diffusion length. In diodes based on vertical transport, absorption enhancement can be obtained by employing Fabry–Perot (F–P) cavities. , More advanced geometries have been proposed to harness the coupling with light, including plasmonic cavities, − guided mode resonators, − F–P resonators, metal–insulator–metal patches, − metasurfaces, , and combinations of these light resonators. By introducing the resonators, the absorption spectrum of the device can be reshaped with respect to that of the absorbing NCs.…”

Emergent properties in supercrystals of atomically precise nanoclusters and colloidal nanocrystals

“…A demonstration of this important paradigm are the difficulties of realising a strong quantum confined Stark effect in NCR ensembles. [242][243][244] In principle, this effect can be very strong in SCs built from zero-dimensional objects. 245 However, if the building blocks exhibit only slight non-uniformities, spectral broadening will occur with deleterious effects on the efficiency of electro-optical modulation.…”

Broadband Enhancement of Mid‐Wave Infrared Absorption in a Multi‐Resonant Nanocrystal‐Based Device

“…Incident light can be trapped in a mode propagating along the substrate either using propagative (guided-mode resonances [7][8][9] ) or evanescent (surface plasmon polariton [5,10,11] ) modes. Alternatively, a Fabry-Perot cavity [12][13][14] or a Bragg mirror [15] can be designed to generate a standing wave that spatially overlaps with the NC film. Consequently, it is possible to reshape the device's photocurrent spectrum and enhance the signal at a given wavelength.…”