We show that Si MOSFETs, AlGaN/GaN HEMTs, AlGaAs/InGaAs HEMTs, and p-diamond FETs with feature sizes ranging from 20 nm to 130 nm could operate at room temperature as THz spectrometers in the frequency range from 120 GHz to 9.3 THz with different subranges corresponding to the transistors with different features sizes and tunable by the gate bias. The spectrometer uses a symmetrical FET with interchangeable source and drain with the rectified THz voltage between the source and drain being proportional to the sine of the phase shift between the voltages induced by the THz signal between gate-to-drain and gate-to-source. This phase difference could be created by using different antennas for the source-to-gate and drain-to gate contacts or by using a delay line introducing a phase shift or even by manipulating the impinging angle of the two antennas. The spectrometers are simulated using the multi-segment unified charge control model implemented in SPICE and ADS and accounting for the electron inertia effect and the distributed channel resistances, capacitances and Drude inductances.
We show that a periodic multi-grated-gate structure can be applied to THz plasmonic FETs (TeraFETs) to improve the THz detection sensitivity. The introduction of spatial non-uniformity by separated gate sections creates regions with distinct carrier concentrations and velocities, giving rise to harmonic behaviors. The resulting frequency spectrum of DC voltage response is composed of enhanced and suppressed regions. In the enhanced region, the amplitude of response voltage can be enlarged up to 100% compared to that in a uniform channel device. The distribution pattern of those regions is dire…
This paper presents an efficient approach for exciting a dielectric resonator antenna (DRA) in the terahertz frequencies by means of a graphene plasmonic dipole. Design and analysis are performed in two steps. First, the propagation properties of hybrid plasmonic onedimensional and two-dimensional structures are obtained by using transfer matrix theory and the finite-element method. The coupling amount between the plasmonic graphene mode and the dielectric wave mode is explored based on different parameters. These results, together with DRA and plasmonic antenna theory, are then used to design…
Terahertz (THz) band is considered as the next frontier in wireless communications. The emerging THz multiplexing techniques are expected to dramatically increase the information capacity of THz communications far beyond a single channel limit. In this work, we explore the THz frequency-division multiplexing modality enabled by novel add-drop multiplexer (ADM) design. Based on modular two-wire plasmonic waveguides fabricated using additive manufacturing and metallization techniques, we demonstrate four-port THz ADMs containing grating-loaded side couplers for operation at ~140 GHz carrier freq…
The terahertz detection performance and operating regimes of graphene plasmonic field-effect transistors (FETs) were investigated by a hydrodynamic model. Continuous wave detection simulations showed that the graphene response sensitivity is similar to that of other materials including Si, InGaAs, GaN, and diamond-based FETs. However, the pulse detection results indicated a very short response time, which favors the rapid/high-sensitively detection. The analysis on the mobility dependence of the response time revealed the same detection regimes as the traditional semiconductor materials, i.e. …
Plasmon oscillations have been intensively studied for more than forty years in conventional two-dimensional electron gas systems in order to find new alternatives to the vacuum devices based on the Smith-Purcell effect in the far-infrared region. However, beside the multiple endeavors, up to date, the plasmon generation in semiconductor heterostructures has been very inefficient. Here we demonstrate that the use of high mobility graphene metamaterials, due to their well-known stronger light-plasmon coupling compared to semiconductor materials can significantly improve the efficiency of far-in…
An electrically tunable terahertz (THz) plasmonic device is designed and fabricated using liquid metals (eutectic gallium indium EGaIn) and shape memory alloy wires (Flexinol). The liquid metal is injected into the voids of a poly(dimethyl) siloxane (PDMS) microfluidic mold forming a periodic array of subwavelength apertures, while the wires are inserted into the elastomer below the metal plane. When a DC voltage is applied to the wires, they contract via Joule heating, reducing the aperture periodicity and blue-shifting the transmission resonances of the device. When the voltage is removed, t…
The new TeraFET design with identical source and drain antennas enables a tunable resonant polarization-sensitive plasmonic spectrometer operating in the sub-terahertz and terahertz (THz) range of frequencies at room temperature. It could be implemented in different materials systems including silicon. The p-diamond TeraFETs support operation in the 200 to 600 GHz windows.
Detectors of terahertz radiation based on field-effect transistors (FETs) are among most promising candidates for low-noise passive signal rectification both in imaging systems and wireless communications. However, it was not realised so far that geometric asymmetry of common FET with respect to source-drain interchange is a strong objective to photovoltage harvesting. Here, we break the traditional scheme and reveal the optimally-asymmetric FET structure providing the maximization of THz responsivity. We fabricate a series of graphene transistors with variable top gate position with respect t…
We studied time resolution and response power dependence of three terahertz detectors based on significantly different types of field effect transistors. We analyzed the photoresponse of custom-made Si junctionless FETs, Si MOSFETs and GaAs-based high electron mobility transistors detectors. Applying monochromatic radiation of high power, pulsed, line-tunable molecular THz laser, which operated at frequencies in the range from 0.6-3.3 THz, we demonstrated that all these detectors have at least nanosecond response time. We showed that detectors yield a linear response in a wide range of radiati…
Metasurfaces, the two-dimensional counterpart of metamaterials, have caught great attention thanks to their powerful capabilities on manipulation of electromagnetic waves. Recent times have seen the emergence of a variety of metasurfaces exhibiting not only countless functionalities, but also a reconfigurable response. Additionally, digital or coding metasurfaces have revolutionized the field by describing the device as a matrix of discrete building block states, thus drawing clear parallelisms with information theory and opening new ways to model, compose, and (re)program advanced metasurface…
Future wireless communication networks have to handle data rates of tens or even hundreds of Gbit/s per link, requiring carrier frequencies in the unallocated terahertz (THz) spectrum. In this context, seamless integration of THz links into existing fiber-optic infrastructures is of great importance to complement the inherent portability and flexibility advantages of wireless networks by the reliable and virtually unlimited capacity of optical transmission systems. On the technological level, this requires novel device and signal processing concepts for direct conversion of data streams betwee…
Driven by a myriad of potential applications such as communications, medical imaging, security, spectroscopy, and so on, terahertz (THz) technology has emerged as a rapidly growing technological field during the last three decades. However, since conventional materials typically used in microwave and optical frequencies are lossy or do not effectively respond at these frequencies, it is essential to find or develop novel materials that are suitable for device applications in the THz range. Therefore, there is wide interest in the community in employing novel naturally-occurring materials, such…
Graphene offers a possibility for actively controlling plasmon confinement and propagation by tailoring its spatial conductivity pattern. However, implementation of this concept has been hampered because uncontrollable plasmon reflection is easily induced by inhomogeneous dielectric environment. In this work, we demonstrate full electrical control of plasmon reflection/transmission at electronic boundaries induced by a zinc-oxide-based dual gate, which is designed to minimize the dielectric modulation. Using Fourier-transform infrared spectroscopy, we show that the plasmon reflection can be va…
The discovery of graphene triggered a rapid rise of unexplored two-dimensional materials and heterostructures having optoelectronic and photonics properties that can be tailored on the nanoscale. Among these materials, black phosphorus (BP) has attracted a remarkable interest thanks to many favorable properties, such as high carrier mobility, in-plane anisotropy, the possibility to alter its transport via electrical gating and direct band-gap, that can be tuned by thickness from 0.3 eV (bulk crystalline) to 1.7 eV (single atomic layer). When integrated in a microscopic field effect transistor …
p-diamond field effect transistors (FETs) featuring large effective mass, long momentum relaxation time and high carrier mobility are a superb candidate for plasmonic terahertz (THz) applications. Previous studies have shown that p-diamond plasmonic THz FETs (TeraFETs) could operate in plasmonic resonant mode at a low frequency window of 200 GHz to ~600 GHz, thus showing promising potential for beyond 5G sub-THz applications. In this work, we explore the advantages of p-diamond transistors over n-diamond, Si, GaN and InGaAs TeraFETs and estimate the minimum mobility required for the resonant p…
We report on room temperature THz detection by means of antenna-coupled field effect transistors fabricated by using epitaxial graphene grown on silicon carbide substrate. Two independent detection mechanisms are found: plasma wave assisted-detection and thermoelectric effect, which is ascribed to the presence of junctions along the FET channel. The superposition of the calculated functional dependence of both the plasmonic and thermoelectric photovoltages on the gate bias qualitatively well reproduces the measured photovoltages. Additionally, the sign reversal of the measured photovoltage dem…
