2D Materials for Terahertz Modulation

Abstract

power consumption and minimizing cross-talk (maintain signal fidelity). As a result, terabit data communication can be made feasible with the help of broadband all-optical devices and circuits. [4] The technology for designing optical components and circuits operating at visible and NIR wavelengths has matured significantly over the last several decades, ensuring their widespread integration. While we can work toward improving data transmission rates of existing communication technology, shortage of spectral bandwidth for data transmission has become a looming problem over time. This has motivated researchers to seek out previously unused portions of the electromagnetic spectrum. The "terahertz gap" (≈30 µm-3 mm) has attracted considerable attention from researchers seeking to bridge the gap between the optical/IR and microwave spectrum. [5,6] Similar to the optical domain, the invention, optimization, and commercialization of discrete components such as sources, modulators, and detectors are necessary for the widespread use and integration of terahertz technologies. Electronic means of terahertz generation utilizing semiconductors (Si, GaAs) IMPATT [7] and Gunn diodes [8] have been developed. In conjunction with a frequency doubler/ tripler circuits, they typically operate on the lower end of the terahertz spectrum (0.1-1 THz); although the power output at higher frequency multiples might be significantly lower as compared to its fundamental mode. Additionally, InGaAs/ InP HBTs and InP HEMTs with cutoff frequencies >600 GHz have been demonstrated. [9,10] The advent of femtosecond lasers has paved the way for the generation of terahertz radiation via photoconductive switches, [11] photo-Dember effect [12,13] and nonlinear optical rectification in organic and inorganic crystals. [14][15][16] Femtosecond lasers have helped develop time domain terahertz systems that have been instrumental in ultrafast spectroscopy to study transient carrier dynamics of semiconductors. Development of terahertz quantum cascade lasers (THz-QCL) employing intersubband transitions in AlGaAs/GaAs quantum wells [17][18][19][20] is a notable milestone in terahertz lasing. In a complementary fashion, terahertz detection could be performed by electro-optic sampling in nonlinear crystals, [21] photoconductive antennas on low-temperature GaAs, [22,23] plasma wave oscillation in a field-effect channel, [24,25] etc. Finally, akin to the compact and economic components available at optical frequencies for the generation, manipulation, and detection, terahertz technology requires Terahertz waves spanning over the 0.1 to 10 THz region of the electromagnetic spectrum have attracted significant attention owing to a variety of potential applications such as short-range high-speed data transmission, noninvasive screening and detection, materials characterization, spectroscopy, etc. This has resulted in massive strides in the development of essential system components such as broadband terahertz sources, detector arrays with high responsivity, as well as...

Silicon‐Based Terahertz Meta‐Devices for Electrical Modulation of Fano Resonance and Transmission Amplitude

“…Generally speaking, THz tunable metamaterials as a whole are controlled by active medium. [ 39–54 ] Modulating the amplitude and phase information of each unit cell in metamaterials could bring more freedom in dynamic control of THz waves. [ 14 ] In sensing applications, the responsivity of a resonance in active medium is determined by its sensitivity, and this should give Fano asymmetric structures a significant advantage in active plasmonics as well.…”

“…[ 39–43 ] On the other hand, by integrating metamaterials with photoactive materials such as silicon on sapphire, graphene, perovskites, and MoS 2 has also shown the active modulation of resonance properties. [ 44–54 ] However, the fabrication of MEMS‐based metamaterials requires sophisticated facilities rather than the conventional photolithography process. The introducing of extra photoactive materials into silicon‐based semiconductor fabrication process would also make it unpractical and expensive.…”

A Phase Transition Oxide/Graphene Interface for Incident‐Angle‐Agile, Ultrabroadband, and Deep THz Modulation

“…Many other functional materials have also been investigated to dynamic control THz transmission, such as doped semiconductor, 2D material, liquid crystals, and phase transition oxides. [ 15–18 ] Wherein, as a typical functional material, VO 2 has attracted great attention and exhibits advanced THz modulation properties, [ 19,20 ] due to its reversible insulator‐to‐metal transition (IMT) and highly flexible excitation methods, including temperature, electric field, laser, stress, etc., [ 21–24 ] accompanied with abrupt conductivity switching of 3–5 orders of magnitude. Until now, the THz E ‐field (electric field) amplitude modulation depth can reach more than 80% with broad operation bandwidth, but it's extremely difficult to achieve higher value despite plenty of efforts have spent to optimize the film fabrication strategies.…”

Materials for Terahertz Optical Science and Technology

“…On the other hand, investigating the properties of THz emissivity enables noninvasive and ultrafast probing of the underlying exotic physical processes in the complex correlated systems such as high-temperature superconductors and several other transition metal oxides (TMOs), as reported by D. S. Rana and M. Tonouchi. The charge injection processes in 2D materials-bulk semiconductor interfaces (such as graphene-Si interface and MoS 2 -Si interface) demonstrate low-threshold, efficient and ultrafast THz modulators (see the progress report on terahertz modulation from P. Gopalan and B. Sensale-Rodriguez [7] ). The works discussed by P. Kuzel et al [3] and D. Zhao et al [4] reveal that in bulk-bandgap semiconductors such as low-dimensional nanocrystals and perovskites, the major contribution to their carrier dynamics and charge transport properties is through change in free carrier density in the material during the interband transition using near-infrared pulses, which also reveals the positive change in THz photoconductivity.…”

“…2020, 8,1901984 enhancing its capabilities as graphene based ultrafast nonlinear optoelectronic devices at THz frequencies (see the progress report from H. A. Hafez et al [6] ). The charge injection processes in 2D materials-bulk semiconductor interfaces (such as graphene-Si interface and MoS 2 -Si interface) demonstrate low-threshold, efficient and ultrafast THz modulators (see the progress report on terahertz modulation from P. Gopalan and B. Sensale-Rodriguez [7] ). Investigations of carrier dynamics in 2D van der Waals (vdW) materials reveal the formation and relaxation of excitons in the strongly correlated heterostructures, which further demonstrates exciting prospects as ultrafast terahertz devices (see the review on terahertz time resolved spectroscopy from P. Han et al [8] ).…”