Dmitry Svintsov

Recent advent of smart photodetectors, where in situ tuning of responsivity enables the reconstruction of light intensity, polarization, and spectrum by a single device, has revolutionized the field of optoelectronics. So far, most such reconstructive detectors were realized with non‐scalable technology of van der Waals stacking. Here, we demonstrate the infrared reconstructive polarimetry with photodetectors based on conventional gated graphene–metal junctions. The reconstruction exploits the gate tuning of polarization contrast, which enables the determination of both infrared power and polarization angle from photovoltage measurements at two different gate voltages. The physics enabling the polarimetry lies in polarization‐dependent shift of the electron hot spot near the contact, and the gate tuning of photosensitive barrier width. We further show the universality of polarization reconstruction, i.e. its feasibility with different geometries of the junction, and with graphene of different quality, from boron–nitride encapsulated flakes to the scalable chemical vapor deposited films.

We demonstrate that the slot between parallel metal gates placed above a two-dimensional electron system (2DES) forms a plasmonic cavity with unconventional mode quantization. The resonant plasmon modes are excited when the slot width L and the plasmon wavelength λ satisfy the condition L=λ/8+n×λ/2, where n=0,1,2…. The lowest resonance occurs at a surprisingly small cavity size, specifically one eighth of the plasmon wavelength, which contrasts with the conventional half-wavelength Fabry-Perot cavities in optics. This unique quantization rule arises from a nontrivial phase shift of -π/4 acquired by the 2D plasmon upon reflection from the edge of the gate. The slot plasmon modes exhibit weak decay into the gated 2DES region, with the decay rate being proportional to the square root of the separation between the gate and the 2DES. The absorption cross section by such slots reaches ∼50% of the fundamental dipole limit without any matching strategies and is facilitated by field enhancement at the metal edges.

Heterostructures comprised of a 2D emitter and collector separated by a dielectric exhibit resonant tunneling when the band structures of both 2D materials are aligned. It is commonly assumed that the height and width of the resonant peak in the tunneling current are determined by electron scattering and rotational misalignment of the 2D materials. In this article, two fundamental factors limiting the maximum height and steepness of the resonance are identified: coupling to the contacts and tunnel splitting of energy levels. The upper limit of the tunneling current is the number of electrons available for tunneling times half the tunnel coupling between the emitter and collector. As a result of a tradeoff between the contact‐induced level broadening and contact resistance, the maximum current is only achievable when the coupling to the contacts equals the tunnel level splitting. According to model calculations, the limiting behavior can be observed in double‐gated graphene/few‐layer hexagonal boron nitride/graphene heterostructures.

Most contemporary architectures of photodetectors based on two-dimensional materials include global gates for carrier density control and local p-n junctions in the channel. We study the dependence of photocurrent in such detectors on the light modulation frequency, fully taking into account the effects of distributed resistance and gate-channel capacitance. The decay of photocurrent with modulation frequency governs the response time. We find that the maximum modulation frequency is largely determined by the position of light-sensitive junction with respect to the middle of the channel. Largest modulation frequency is achieved for junctions in immediate vicinity of either source or drain contacts, while fast roll-off of the modulation characteristic is observed for junction in the middle of the channel.

We present a combined experimental and theoretical study of photovoltage generation in a bilayer graphene (BLG) transistor structure exposed to subterahertz radiation. The device possesses a global bottom and split top gate, enabling the formation of a tunable p–n junction with controllable band gap and carrier densities at both sides. Measurements show that the photovoltage arises primarily through a thermoelectric mechanism driven by heating of the p–n junction in the middle of the channel. We provide a theoretical justification for the excitation of two-dimensional plasmons at a record-low frequency of 0.13 THz, which manifests itself as characteristic oscillations in the measured photovoltage. These plasmonic oscillations, activated by a decrease in charge carrier concentration due to opening of the band gap, lead to a local enhancement of the electromagnetic field and an increase in the carrier temperature in the junction region. The record-low frequency of plasmon resonance is enabled by the low carrier density achievable in the bilayer graphene upon electrical induction of the band gap.

We study the interplay of electron-phonon and electron-impurity scattering in graphene and its manifestations in thermopower S. Electron scattering by acoustic phonons dominating in clean samples results in energy-independent carrier diffusivity, which translates into zero value of S. Inclusion of charged impurities plays a twofold role. At low impurity densities, the diffusivity becomes energy-dependent, which elevates S. In largely disordered samples, the carrier density becomes inhomogeneous, which results in self-averaging of thermopower. The latter effect is tackled here with effective medium theory, and predicts a slow drop in S with increasing the impurity density. The competition of these effects results in thermopower maximization at an optimal density of impurities n_imp. The latter is estimated as 2 × 10¹¹ cm^–2 at room temperature, which corresponds to the highest-quality chemical vapor deposited graphene.

Mid-infrared (mid-IR) photodetectors play a crucial role in various applications, including the development of biomimetic vision systems that emulate neuronal function. In this work, we demonstrate a new infrared photodetector based on graphene/boron nitride/graphene tunneling heterostructure combining perception and memory functions. The detection principle is based on the shift of the N -shaped tunneling resonant feature in the I - V –curve upon infrared illumination. In the current-biased mode, such a shift results in a strong voltage “jump” (0.05−1 V) to another branch of the I - V –characteristic that persists after switching the radiation off. As a result, the structure can be considered as a visual neuron that combines perception and memory functions. More interestingly, the direction of voltage switching depends on laser beam position, adding extra recognition functionality to our perception device. The observed phenomena are explained within the theory of selective light-induced heating of electrons in the graphene layers, and the tunneling of hot carriers.

We present a combined experimental and theoretical study of photovoltage generation in a bilayer graphene (BLG) transistor structure exposed to subterahertz radiation. The device features a global bottom and split top gate, enabling independent control of the band gap and Fermi level, thereby enabling the formation of a tunable p-n junction in graphene. Measurements show that the photovoltage arises primarily through a thermoelectric mechanism driven by heating of the p-n junction in the middle of the channel. We also provide a theoretical justification for the excitation of two-dimensional plasmons at a record-low frequency of 0.13 THz, which manifests itself as characteristic oscillations in the measured photovoltage. These plasmonic resonances, activated by a decrease in charge carrier concentration due to opening of the band gap, lead to a local enhancement of the electromagnetic field and an increase in the carrier temperature in the junction region. The record-low frequency of plasmon resonance is enabled by the low carrier density achievable in the bilayer graphene upon electrical induction of the band gap.