In this paper, we analyze the modulation characteristics and the ultimate modulation frequency of the terahertz (THz) hot-electron FET bolometers with the graphene channels (GCs), metal gate (MG), and gate barrier layers (BLs) in a wide temperature range. Our results predict that the responsivity of GC-FET bolometers decreases with decreasing operating temperature. This is attributed to a dramatic drop in the thermionic GC-MG current (characterized by the relatively large activation energy) and its modulated component when the temperature lowers. A further decrease in the temperature results in a fairly strong responsivity roll-off. In contrast, the responsivity of the GC-FET detectors with the temperature-adjusted load resistance rises with decreasing temperature because the temperature lowering leads to an increase in the electron energy relaxation time and promotes more effective heating by the impinging THz radiation. In this case, the weakening of the thermionic current is compensated by the commensurate increase in the load resistance.

We propose and analyze the terahertz (THz) bolometric vector detectors based on the graphene-channel field-effect transistors (GC-FET) with the black-P gate barrier layer or with the composite b-BN/black-P/b-BN gate layer. The phase difference between the signal received by the FET source and drain substantially affects the plasmonic resonances. This results in a resonant variation of the detector response on the incoming THz signal phase shift and the THz radiation angle of incidence.

In this work we address the problem of reidentifying vehicles moving on a highway in thermal infrared spectrum. The vehicle images are collected at the different locations on the highway, and the collection timestamp is served as the weak supervisory signal to allow the training of the vehicle reidentification network. Combined with the vehicle detection network trained on RGB images, the system allows fully automatic training and testing of the reidentification network in thermal infrared spectrum. The experiments confirm the advantage of the proposed method over using identical reidentification network trained on RGB images. This approach can be used for the tasks where the labelled training data is sparse or unavailable, as in the examples of thermal infrared or multispectral infrared sensors.

With the rapid advancement of Artificial Intelligence-driven object recognition, the development of cognitive tunable imaging sensors has become a critically important field. In this paper, we demonstrate an infrared (IR) sensor with spectral tunability controlled by the applied bias between the long-wave and mid-wave IR spectral regions. The sensor is a Quantum Well Infrared Photodetector (QWIP) containing asymmetrically doped double QWs where the external electric field alters the electron population in the wells and hence spectral responsivity. The design rules are obtained by calculating the electronic transition energies for symmetric and antisymmetric double-QW states using a Schrödinger–Poisson solver. The sensor is grown and characterized aiming detection in mid-wave (~5 µm) to long-wave IR (~8 µm) spectral ranges. The structure is grown using molecular beam epitaxy (MBE) and contains 25 periods of coupled double GaAs QWs and Al0.38Ga0.62As barriers. One of the QWs in the pair is modulation-doped to provide asymmetry in potential. The QWIPs are tested with blackbody radiation and FTIR down to 77 K. As a result, the ratio of the responsivities of the two bands at about 5.5 and 8 µm is controlled over an order of magnitude demonstrating tunability between MWIR and LWIR spectral regions. Separate experiments using parameterized image transformations of wideband LWIR imagery are performed to lay the framework for utilizing tunable QWIP sensors in object recognition applications.

We propose and model the terahertz bolometric detectors based on the graphene-channel field-effect transistors (GC-FETs) with the black-Phosphorus/hexagonal-Boron Nitride (b-P/h-BN) barrier layers. The GC is encapsulated in h-BN with a narrow b-P window (collector window) in the gate layer. The proposed device structure enables decreased electron scattering due to the elevated quality of the interfaces and promotes a more pronounced plasmonic response of the two-dimensional electron system in the GC. This improves the THz detector performance at the plasmonic resonances. Narrowing the collector window diminishes the Peltier effect and improves the detector characteristics.

We present electrical properties of heavily doped and completely compensated Ge films grown on semiinsulating GaAs(100) substrates by vacuum evaporation. The thin (∼100 nm) Ge films are single-crystal and characterized using temperature-dependent transport measurements, with anomalously large activation energy up to half the Ge bandgap, anisotropy of the transverse magnetoresistance, high resistivity (up to 140 Ω cm), low free charge carrier mobility (∼50 cm2/V·s), and concentration (∼1014–1015 cm−3). This behaviour is attributed to a completely compensated semiconductors arising from Ga and As impurity incorporation and large-scale potential fluctuations. Analysis suggests a two-dimensional percolative transport mechanism in Ge-on-GaAs heterostructures.

We present and generalize the preparation conditions and properties of strongly compensated Ge films grown on semi-insulating GaAs(100) substrates by vacuum evaporation. The films are characterized using high-resolution X-ray diffraction (HRXD), atomic force (AFM) and Kelvin probe force microscopy (KPFM), Raman spectroscopy, electroreflectance, optical absorption and temperature-dependent transport measurements. HRXD shows that an ideally pseudomorphic growth of Ge films with good single crystal structure can be obtained by this growth technique. The film microstructure and transport properties are found to depend sensitively on the Ge deposition rate. Thin ( 100 nm) Ge films grown at low rates exhibit rough, granular morphology (RMS up to 15 nm), high resistivity (up to 140 Ω·cm), low free charge carrier mobility ( 50 cm2/V·s) and concentration ( 1014–1015 cm−3) and activated conductivity with an anomalously large activation energy up to half the Ge bandgap. This insulating behavior is attributed to a completely compensated, disordered state arising from Ga and As impurity incorporation and large-scale potential fluctuations. Analysis suggests a two-dimensional percolative transport mechanism, consistent with the reduced film thickness and disorder-induced carrier localization. In contrast, films deposited at higher rates are smoother, more conductive, and exhibit weak temperature dependence of the resistivity, indicative of a more ordered state. These results provide insight into the interplay between disorder, carrier localization, and transport in heavily compensated semiconductors, and highlight the critical role of growth kinetics in determining the properties of Ge-on-GaAs heterostructures.

We analyze the operation of the hot-electron FET bolometers with the graphene channels (GCs) and the gate barrier layers. Such bolometers use the thermionic emission of the hot electrons heated by incident-modulated THz radiation. The hot electrons transfer from the GC into the metal gate. As the THz detectors, these bolometers can operate at room temperature. We show that the response and ultimate modulation frequency of the GC-FET bolometers are determined by the efficiency of the hot-electron energy transfer to the lattice and the GC side contacts due to the 2DEG lateral thermal conductance. The dependences of these mechanisms on the band structure and geometrical parameters open the way for the GC-FET bolometers optimization, in particular, for the enhancement of the maximum modulation frequency.

This paper reviews recent advances in the research and development of graphene-layer (GL) based van der Waals (vdW) two-dimensional (2D) heterostructures for fast, sensitive terahertz (THz) detection. 2D plasmonic nonlinearity as well as photothermoelectric effects in GL and other Dirac semimetals/semiconductors are promising mechanisms for highly sensitive, fast-response, room-temperature THz detection. The vertical GL and b-AsxP1-x heterostructures enable a new ultrafast bolometric mechanism enhancing the GL-based THz photodetector performance. We also introduce our recently developed GL- and other Dirac-semimetal/semiconductor-based rectenna FET structures, supporting a so-called 3D rectification mechanism. This mechanism supports fast and highly sensitive zero-power consumption extremely low-noise THz detection, which was experimentally verified, with further experiments in progress.

We propose the terahertz (THz) detectors based on field-effect transistors (FETs) with the graphene channel (GC) and the black-Arsenic (b-As) black-Phosphorus (b-P), or black-Arsenic-Phosphorus (b-As (x) P (1-x)) gate barrier layer. The operation of the GC-FET detectors is associated with the carrier heating in the GC by the THz electric field resonantly excited by incoming radiation leading to an increase in the rectified current between the channel and the gate over the b-As xP 1-x energy barrier layer (BLs). The specific feature of the GC-FETs under consideration is relatively low energy BLs and the possibility to optimize the device characteristics by choosing the barriers containing a necessary number of the b-As x P 1-x atomic layers and a proper gate voltage. The excitation of the plasma oscillations in the GC-FETs leads to the resonant reinforcement of the carrier heating and the enhancement of the detector responsivity. The room temperature responsivity can exceed the values of 10(3) A/W. The speed of the GC-FET detector's response to the modulated THz radiation is determined by the processes of carrier heating. As shown, the modulation frequency can be in the range of several GHz at room temperatures.

We analyze the two-dimensional electron gas (2DEG) heating by the incident terahertz (THz) radiation in the field-effect transistor (FET) structures with the graphene channels (GCs) and the black-phosphorus and black-arsenic gate barrier layers (BLs). Such GC-FETs can operate as bolometric THz detectors using the thermionic emission of the hot electrons from the GC via the BL into the gate. Due to the excitation of plasmonic oscillations in the GC by the THz signals, the GC-FET detector response can be pronouncedly resonant, leading to elevated values of the detector responsivity. The lateral thermal conductivity of the 2DEG can markedly affect the GC-FET responsivity, in particular, its spectral characteristics. This effect should be considered for the optimization of the GC-FET detectors.

We investigate the response of the micromechanical field-effect transistors (MMFETs) to the impinging terahertz (THz) signals. The MMFET uses the microcantilevers (MC) as a mechanically floating gate and the movable mirror of the Michelson optical interferometer. The MC mechanical oscillations are transformed into optical signals and the MMFET operates as the detector of THz radiation with the optical output. The combination of the mechanical and plasmonic resonances in the MMFET with the optical amplification enables an effective THz detection.

Abstract We propose the terahertz (THz) detectors based on field-effect transistors (FETs) with the graphene channel (GC) and the black-Arsenic (b-As) black-Phosphorus (b-P), or black-Arsenic-Phosphorus (b-As $$_x$$ x P $$_{1-x}$$ 1 - x ) gate barrier layer. The operation of the GC-FET detectors is associated with the carrier heating in the GC by the THz electric field resonantly excited by incoming radiation leading to an increase in the rectified current between the channel and the gate over the b-As $$_x$$ x P $$_{1-x}$$ 1 - x energy barrier layer (BLs). The specific feature of the GC-FETs under consideration is relatively low energy BLs and the possibility to optimize the device characteristics by choosing the barriers containing a necessary number of the b-As $$_x$$ x P $$_{1-x}$$ 1 - x atomic layers and a proper gate voltage. The excitation of the plasma oscillations in the GC-FETs leads to the resonant reinforcement of the carrier heating and the enhancement of the detector responsivity. The room temperature responsivity can exceed the values of $$10^3$$ 10 3 A/W. The speed of the GC-FET detector’s response to the modulated THz radiation is determined by the processes of carrier heating. As shown, the modulation frequency can be in the range of several GHz at room temperatures.

A novel terahertz (THz) hot-electron bolometric detector based on a graphene field effect transistor with the black-AsP gate barrier layer (BL) is proposed and evaluated theoretically. By providing a relatively low energy barrier for the emitted electrons the b-AsP BL helps reinforce the THz radiation absorption and the intensification of the electron heating and thermionic emission associated with the resonant excitation of plasmonic oscillations in the graphene channel.

Artificial Intelligence-based object recognition in the infrared spectrum region is essential for autonomous applications and will likely require on-demand spectral tuning of an imaging sensor. Here we develop a quantum well infrared photodetector (QWIP) with an asymmetrically doped double quantum well (QW) array which provides the means to control its spectral sensitivity with an applied bias. The test structures were designed using a Schrödinger-Poisson solver to find the electronic transition energies for symmetric and antisymmetric double-QW states. The design, growth, and characterization of QWIPs have been performed aiming at the 5-8 μm and 8-12 μm detection wavelengths. The structures were grown by molecular beam epitaxy and contained 25 periods of coupled double GaAs QWs and AlxGa1-xAs barriers. One of the QWs in the pair was doped to provide potential asymmetry allowing for control of the electron population on the split levels by the bias applied to the QWIP. The QW structures were calibrated using TEM, and tested with blackbody radiation and FTIR down to 77 K. As a result, the ratio of the responsivities of the two bands at about 8 and 11 μm as well as 5 and 8 μm was controlled with up to an order of magnitude by the applied bias within +/- 4V.

The object recognition in thermal infrared spectrum can possibly be enhanced by capturing radiation signals in narrower subbands of this spectrum and performing recognition in color or multiple channel thermal infrared images. In this work, we investigate possible benefits of 2-channel thermal infrared images captured by commercial cameras. We performed experiments on our collected images containing persons and cars. Fusion of object recognition results obtained in different channels separately, gives some improvement over the use of a recognizer with single channel full spectrum images. We also present a proof-of-concept design of adaptable thermal imager based on asymmetrically-doped double quantum well arrays, which can efficiently capture multiband images in the future.

We propose and analyze the performance of terahertz (THz) room-temperature bolometric detectors based on the graphene channel field-effect transistors (GC-FET). These detectors comprise the gate barrier layer (BL) composed of the lateral hexagonal-boron nitride black-phosphorus/hexagonal-boron nitride (h-BN/b-P/h-BN) structure. The main part of the GC is encapsulated in h-BN, whereas a short section of the GC is sandwiched between the b-P gate BL and the h-BN bottom layer. The b-P gate BL serves as the window for the electron thermionic current from the GC. The electron mobility in the GC section encapsulated in h-BN can be fairly large. This might enable a strong resonant plasmonic response of the GC-FET detectors despite relatively lower electron mobility in the GC section covered by the b-P window BL. The narrow b-P window diminishes the Peltier cooling and enhances the detector performance. The proposed device structure and its operation principle promote elevated-temperature GC-FET THz detector responsivity values and other characteristics, especially at the plasmonic resonances.

The interband Zener-Klein interband tunneling in the field-effect transistors (FETs) with the graphene channels consisting of the reverse-biased p-i-n junctions enables the negative dynamic conductance associated with the electrons and hole propagation delays. This can lead to the self-excitation of plasmons in the gated p- and n-regions. For the submicrometer gate lengths, the frequency of these plasmons is in the terahertz (THz) range. The plasmon self-excitation in this regime can be used for the generation of THz radiation.

We evaluate the terahertz (THz) detectors based on field effect transistor (FET) with the graphene channel {GC} and a floating metal gate (MG) separated from the GC by a black-phosphorus (b-P) or black-arsenic (b-As) barrier layer (BL). The operation of these GC-FETs is associated with the heating of the two-dimensional electron gas in the GC by impinging THz radiation leading to thermionic emission of the hot electrons from the GC to the MG. This results in the variation of the floating gate potential, which affects the source-drain current. At the THz radiation frequencies close to the plasmonic resonance frequencies in the gated GC, the variation of the source-drain current and, hence, the detector responsivity can be resonantly large.

This paper revies recent advances in the research of graphene Dirac plasmons (GDPs) for THz device applications particularly focusing on THz laser transistors.