pW Hz Research Articles

Magnetic Field Enhanced Frequency‐Selective Terahertz Detection via 3D Printing Micro‐Helical Stepped and MoTe2 Coated Arrays

AbstractRecent advancements in wireless communication have markedly increased data throughput and decreased latency in progressing toward sixth‐generation (6G) networks, wherein the terahertz (THz) waveband offers significant potential. However, conventional THz sensors often suffer from high noise, low responsivity, and low spectrum efficiency, limiting their effectiveness for THz applications. Here, to address these challenges, a magnetic‐enhanced frequency‐selective is developed THz sensor by depositing an Au‐enhanced active layer of MoTe2 on a designed 3D printing high‐depth micro‐helical stepped structure. This sensor, featuring four characteristic frequency points and an effective area of 107.12 mm2, demonstrated noticeable improvements under a 0.145 mT magnetic field at 0.1 THz: optical responsivity improved by 413.23% (from 3.32 to 17.03 MV W−1), noise equivalent power decreased by 80.51% (from 49.16 to 9.58 pW Hz−1/2), and the detectivity reached 3.30 × 1010 cm·Hz1/2·W−1. This work highlights the potential of integrating 3D microstructures with novel topological materials for practical 6G communication.

Enhancing Self‐Powered Terahertz Photodetection with VSe2 and Van Der Waals Heterostructure Integration via Photothermoelectric Effect

AbstractOwning unique optical and electronic properties, two dimensional (2D) materials have made remarkable strides in the field of photodetection applications. However, achieving highly sensitive and ultra‐broadband detection from microwave to terahertz (THz) range (0.02–0.54 THz) remains a significant challenge for photodetectors. This study presents a self‐powered THz photodetector based on VSe2 and its van der Waals heterostructure. The photoresponse of the photodetector is primarily attributed to the photothermoelectric effect. At room temperature, the device exhibits lower noise equivalent power values of 21 pW Hz−1/2 at 0.28 THz. This work has achieved ultra‐broadband detection and demonstrated the potential for large‐area imaging, providing a new avenue for the application of THz technology in nondestructive testing and biometric identification fields.

A High-Performance Thin-Film Sensor in 6G for Remote Sensing of the Sea Surface

Functional devices in the THz band will provide a highly important technical guarantee for the promotion and application of 6G technology. We sought to design a high-performance sensor with a large area, high responsiveness, and low equivalent noise power, which is stable at room temperature for long periods and still usable under high humidity; it is suitable for the environment of marine remote sensing technology and has the potential for mass production. We prepared a Te film with high stability and studied its crystallization method by comparing the sensing and detection effects of THz waves at different annealing temperatures. It is proposed that the best crystallization and detection effect is achieved by annealing at 100 °C for 60 min, with a sensitivity of up to 19.8 A/W and an equivalent noise power (NEP) of 2.8 pW Hz−1/2. The effective detection area of the detector can reach the centimeter level, and this level is maintained for more than 2 months in a humid environment at 30 °C with 70–80% humidity and without encapsulation. Considering its advantages of stability, detection performance, large effective area, and easy mass preparation, our Te thin film is an ideal sensor for 6G ocean remote sensing technology.

Large Area Flexible Thin Layer Terahertz Detector

AbstractDue to the low photon energy in the relevant frequency band, fewer materials can directly excite carriers, and an extreme lack of high‐performance, large‐area detectors, limit the promotion, and development of 6G technology. In addition, flexible detectors with the integration of 6G communication and Internet of Things technology has good prospects for application in the development of optoelectronic devices, which are also urgently needed. A large‐area flexible thin layer terahertz detector is designed that combines the advantages of excellent optoelectronic performance in the detection of electromagnetic waves with low photon energy and the localized surface plasmon (LSP) effect in a sub‐wavelength structure detector. Due to the large effective area, the spiral electrode device demonstrates the best performance at room temperature. The noise equivalent power (NEP) and photoresponsivity (RV) are achieved with 0.4 pW Hz−1/2 and 154 MV W−1 at 0.28 THz. In addition, the bending experiments show that the device has extreme advantages for flexible 6G detector applications.

Preparation of hierarchical MOF-5 films using morphology controlled ZnO coatings for temperature dependent optical sensors application

Morphology and well-organized hierarchical structures are so effective on the properties of materials and their device applications. Herein, the metal organic framework (MOF-5) has been prepared by solvothermal transformation of nanostructured zinc oxides (ZnO) with different morphologies including nanorods (NRs), hollow spheres (HSs) and porous spheres (PSs). The SEM image indicates growth of MOF-5 sheets around the ZnO NRs with straight hexagonal arrangement. X-ray diffraction (XRD) illustrates the good crystal structure of MOF-5 grown around the ZnO NRs with a dominant crystal orientation (220). Moreover, the morphology and crystalline properties of the ZnO NRs remained intact after the deposition of MOF-5 structures. The photoluminescence (PL) properties of the MOF-5/ZnO film show a slight improvement compared to both the ZnO and MOF-5 components, which must originate from the improved transfer of charge carriers between the MOF-5 and ZnO NRs. The sensitivity and detectivity 5.6 and 1.2 times increased by decreasing temperature from 300 K to 285 K. Finally, a metal-semiconductor-metal (MSM) photodetector based on MOF-5/ZnO NRs was prepared. The optoelectrical behavior of the device is determined through current-voltage (I–V) and time-volage (t-V) curves under UV illumination at different temperatures. The MOF-5/ZnO MSM photodetectors are a temperature-dependent photodetector with excellent UV photosensitivity at lower temperatures. The voltage responsivity was 43.64 and 70.73 kV W−1 at 300 K and 285 K, respectively. NEP and detectivity was measured 15.53 pW Hz−1/2 and 2.03 × 108 Hz−1/2w−1 at 285K respectively.

Fast Switching of Bolometric and Self‐Powered Effects in 2H‐NbSe2 for High‐Efficiency Low‐Energy Photon Harvesting

AbstractThe high‐performance detector that operates at the low‐photon‐energy range (≈meV) of the electromagnetic spectrum at room temperature remains in urgent demand for application in a variety of important sectors, including 6G communications, security, sensing, medicine, space science, etc. The vast range of 2D‐layered nanomaterials and their distinct layer structures provide an ideal foundation for the manufacture of sophisticated photodetectors and detectors with convenient fabrication methods. In this paper, the direct detection of terahertz waveband dominated by the bolometer effect and photo‐thermoelectric effect is demonstrated, which is endowed with a versatile integration of 2H‐NbSe2 in terms of planar and vertical van der Waals structures. This 2H‐NbSe2‐based device can detect broadband long wavelength due to the bolometer effect, and the van der Waals heterostructure‐based device exhibits excellent sensitivity and self‐powered photo‐thermoelectric conversion with high responsivity (>735 V W−1), low response time (<1 µs), as well as low noise equivalent power (NEP < 50 pW Hz−0.5) at room temperature. The photodetector engineers versatile detection mechanisms, displaying low‐energy photons on the hybrid integration of novel low‐dimensional materials and providing an opportunity for the practical application of energy harvesting.

Wafer‐scale patterned growth of type‐II Dirac semimetal platinum ditelluride for sensitive room‐temperature terahertz photodetection

AbstractAs the lastly unexplored electromagnetic wave, terahertz (THz) radiation has been exploited in a plenty of contexts such as fundamental research, military and civil fields. Most recently, representative two‐dimensional (2D) topological semimetal, platinum ditelluride (PtTe2) has attracted considerable research interest in THz detection due to its unique physical properties. However, to achieve practical applications, the low‐cost, large‐scale, controllable synthesis and efficient patterning of 2D materials are key requirements, which remain a challenge for PtTe2 and its photodetectors (PDs). Herein, a facile approach is developed to obtain wafer‐scale (2‐inches) patterned PtTe2 arrays using one‐step tellurium‐vapor transformation method and micro‐Nano technology. PtTe2 PD arrays are fabricated with the as‐grown PtTe2 arrays evenly distributed on a 2‐inch wafer, exhibiting high conductivity (~2.7 × 105 S m−1) and good electrical consistency. Driven by the Dirac fermions, PtTe2 PDs achieve a broadband (0.02–0.3 THz) response with a fast response speed (~4.7 μs), a high sensitivity (~47 pW Hz−1/2) and high‐resolution transmission THz‐imaging capability, which displays the potential of large‐area THz array imaging. These results are one step towards the practical applications of integrated PD arrays based on 2D materials.image

Excitonic Insulator Enabled Ultrasensitive Terahertz Photodetection with Efficient Low-Energy Photon Harvesting.

Despite the interest toward the terahertz (THz) rapidly increasing, the high-efficient detection of THz photon is not widely available due to the low photoelectric conversion efficiency at this low-energy photon regime. Excitonic insulator (EI) states in emerging materials with anomalous optical transitions and renormalized valence band dispersions render their nontrivial photoresponse, which offers the prospect of harnessing the novel EI properties for the THz detection. Here, an EI-based photodetector is developed for efficient photoelectric conversion in the THz band. High-quality EI material Ta2 NiSe5 is synthesized and the existence of the EI state at room temperature is confirmed. The THz scanning near-field optical microscopy experimentally reveals the strong light-matter interaction in the THz band of EI state in the Ta2 NiSe5 . Benefiting from the strong light-matter interaction, the Ta2 NiSe5 -based photodetectors exhibit superior THz detection performances with a detection sensitivity of ≈42 pW Hz-1/2 and a response time of ≈1.1 µs at 0.1 THz at room temperature. This study provides a new avenue for realizing novel high-performance THz photodetectors by exploiting the emerging EI materials.

A van der Waals heterostructure based on nickel telluride and graphene with spontaneous high-frequency photoresponse

Terahertz detectors have potential applications in various fields including security inspection, biomedicine, and noninvasive quality inspection due to their ability to detect terahertz radiation. However, traditional detection materials have reached their bottlenecks due to difficulties in the breakthrough of fundamental principles for terahertz light. In this work, a terahertz detector based on a NiTe2–graphene van der Waals heterostructure has been developed to inhibit the dark current and thermal-agitation noise at room temperature. The hetero-integration of NiTe2 and graphene exhibits enhanced photon-absorption ability and its downconversion into a direct current. The experimental results show that the peak photoresponsivity of our photodetector is 1.31 A W−1 at 0.28 THz, and the corresponding noise equivalent power is 17.56 pW Hz−1/2, which rivals commercially thermal-based photodetectors. Our device has already shown capabilities of large-area imaging, fast speed, and high signal-to-noise ratio, which can be rendered as an important step for exploring topological semimetal optoelectronics.

Micromechanical Bolometers for Subterahertz Detection at Room Temperature.

Fast room-temperature imaging at terahertz (THz) and subterahertz (sub-THz) frequencies is an interesting technique that could unleash the full potential of plenty of applications in security, healthcare, and industrial production. In this Letter, we introduce micromechanical bolometers based on silicon nitride trampoline membranes as broad-range detectors down to sub-THz frequencies. They show, at the longest wavelengths, room-temperature noise-equivalent powers comparable to those of state-of-the-art commercial devices (∼100 pW Hz–1/2), which, along with the good operation speed and the easy, large-scale fabrication process, could make the trampoline membrane the next candidate for cheap room-temperature THz imaging and related applications.

Hot-carrier infrared detection in PbS with ultrafast and highly sensitive responses

Traditional infrared semiconductors with direct narrow bandgaps, such as HgCdTe, InGaAs, and lead salts (PbS, PbSe, and PbTe), have been commercialized for decades in various infrared technologies, such as night vision, military communication, and health monitoring. However, traditional infrared (specifically middle- and long-wave infrared) semiconductors suffer from serious noise generation via thermal excitation and external current bias. Although thermal infrared detectors can operate at room temperature, their response speed is very slow, typically on the order of milliseconds or worse, which limits their applications. Herein, we reinvent a classical lead salt semiconductor (PbS) as a room temperature, high speed, and high-detectivity infrared detector. The detection is operated via the self-driven (no bias voltage necessary) photothermoelectric (PTE) effect with a response time reaching 500 ns (limited by the measurement setup)—three orders of magnitude faster than commercial PTE and photoconductive PbS detectors. Furthermore, the physical principle of hot-carrier-dominated heat energy conversion is proposed to understand the unconventional ultrafast response behavior. Combined with high sensitivity at room temperature (noise equivalent power 0.3 pW Hz−1/2) and broadband detection range (0.4–2.3 μm), this hot carrier makes the traditional commercial semiconductor PbS applicable to a class of infrared detection applications.

Broadband Photodetectors: Broadband Bi2O2Se Photodetectors from Infrared to Terahertz (Adv. Funct. Mater. 14/2021)

In article number 2009554, Man Luo, Peng Wang, Zhiming Huang, and co-workers demonstrate a room-temperature 2D Bi2O2Se photodetector with ultrafast (476 ns) and ultralow noise (0.2 pW Hz−1/2) for broadband detection. In the infrared regions, the nonequilibrium carriers result from photo-induced electron-hole pairs in Bi2O2Se. While in the THz region, the nonequilibrium electrons are injected from the metal electrodes to Bi2O2Se by the electromagnetic induced well under the THz wave.

Broadband Bi2O2Se Photodetectors from Infrared to Terahertz

Abstract2D Bi2O2Se has shown great potential in photodetector from visible to infrared (IR) owing to its high mobility, ambient stability, and layer‐tunable bandgaps. However, for the terahertz (THz) band with longer wavelength and richer spectral information, there are few reports on the research of THz detection based on 2D materials. Herein, an antenna‐assisted Bi2O2Se photodetector is constructed to achieve broadband photodetection from IR to THz ranges driven by multi‐mechanism of electromagnetic waves to electrical conversion. The good tradeoff between the bandgap and high mobility results in a broad spectral detection. In the IR region, the nonequilibrium carriers result from photo‐induced electron‐hole pairs in the Bi2O2Se body. While in the THz region, the carriers are caused by the injected electrons from the metal electrodes by the electromagnetic‐induced well. The Bi2O2Se photodetector achieves a broadband responsivity of 58 A W‐1 at 1550 nm, 2.7 × 104 V W‐1 at 0.17 THz, and 1.9 × 108 V W‐1 at 0.029 THz, respectively. Surprisingly, an ultrafast response time of 476 ns and a quite low noise equivalent power of 0.2 pW Hz−1/2 are acquired at room temperature. Our researches exhibit promising prospects of Bi2O2Se in broadband detection, THz imaging, and ultrafast sensing.

Thermoelectric graphene photodetectors with sub-nanosecond response times at terahertz frequencies

AbstractUltrafast and sensitive (noise equivalent power <1 nW Hz−1/2) light-detection in the terahertz (THz) frequency range (0.1–10 THz) and at room-temperature is key for applications such as time-resolved THz spectroscopy of gases, complex molecules and cold samples, imaging, metrology, ultra-high-speed data communications, coherent control of quantum systems, quantum optics and for capturing snapshots of ultrafast dynamics, in materials and devices, at the nanoscale. Here, we report room-temperature THz nano-receivers exploiting antenna-coupled graphene field effect transistors integrated with lithographically-patterned high-bandwidth (∼100 GHz) chips, operating with a combination of high speed (hundreds ps response time) and high sensitivity (noise equivalent power ≤120 pW Hz−1/2) at 3.4 THz. Remarkably, this is achieved with various antenna and transistor architectures (single-gate, dual-gate), whose operation frequency can be extended over the whole 0.1–10 THz range, thus paving the way for the design of ultrafast graphene arrays in the far infrared, opening concrete perspective for targeting the aforementioned applications.

A fast and sensitive room-temperature graphene nanomechanical bolometer

Bolometers are a powerful means of detecting light. Emerging applications demand that bolometers work at room temperature, while maintaining high speed and sensitivity, properties which are inherently limited by the heat capacity of the detector. To this end, graphene has generated interest, because it has the lowest mass per unit area of any material, while also possessing extreme thermal stability and an unmatched spectral absorbance. Yet, due to its weakly temperature-dependent electrical resistivity, graphene has failed to challenge the state-of-the-art at room temperature. Here, in a departure from conventional bolometry, we use a graphene nanoelectromechanical system to detect light via resonant sensing. In our approach, absorbed light heats and thermally tensions a suspended graphene resonator, thereby shifting its resonant frequency. Using the resonant frequency as a readout for photodetection, we achieve a room-temperature noise-equivalent power (2 pW Hz−1/2) and bandwidth (from 10 kHz up to 1.3 MHz), challenging the state-of-the-art.

Anomalous Broadband Spectrum Photodetection in 2D Rhenium Disulfide Transistor

Abstract2D transition metal dichalcogenide (TMD)‐based phototransistors generally work under photoconductive, photovoltaic, or photogating mode, in which photocarriers are generated from band‐to‐band excitation. Nevertheless, due to the relatively large bandgap, most TMD phototransistors working under these modes are restricted in visible spectrum. Here, photodetection in 2D multilayer rhenium disulfide (ReS2) transistor via bolometric mode, which relies on light heating induced conductance change instead of band‐to‐band photoexcitation is reported, making it possible for sub‐bandgap photon detection. The bolometric effect induced photoresponse is first revealed by an anomalous sign switching of photocurrent from positive to negative while increasing gate voltage under visible light, which is further validated by the temperature dependent electrical transport measurements. The phototransistor exhibits remarkable photoresponse under infrared regime, beyond the optical bandgap absorption edge of the ReS2 flake. Additionally, it demonstrates a low noise equivalent power, less than 5 × 10−2 pW Hz−1/2, which is very promising for ultra‐weak light detection. Moreover, the response time is below 3 ms, nearly 3–4 orders of magnitude faster than previously reported ReS2 photodetectors. The findings promise bolometric effect as an effective photodetection mode to extend the response spectrum of large bandgap TMDs for novel and high‐performance broadband photodetectors.

Distinctive Performance of Terahertz Photodetection Driven by Charge‐Density‐Wave Order in CVD‐Grown Tantalum Diselenide

AbstractThe quantum behavior of carriers in solid is the foundation of modern electronic and optoelectronic technology, but it is still facing huge challenges within inherited single‐particle quantum processes working at the millimeter wave/terahertz (THz) band. Here, a straightforward strategy for the direct detection of millimeter wave/THz photons in a sub‐wavelength metal‐TaSe2‐metal structure under strong interaction with a localized field of surface plasmon is proposed. By breaking the inversion symmetry under the perturbations of electric field and atomic reconstruction from van der Waals integration, the nonequilibrium electronic states under a radiant field can be manipulated in a collective fashion, leading to a large photocurrent responsivity over 40 A W−1 and noise equivalent power less than 1 pW Hz−1/2 even at room temperature. A more than 40‐fold enhancement in responsivity is achieved when transitioning from the normal phase to the CDW phase. The findings shed fresh light on the understanding of the delicate balance in the charge‐ordered phase, and facilitate the exploitation of a correlated electron system for optoelectronic applications in fields of security, remote sensing, and imaging.

Investigation of silicon-on-insulator CMOS integrated thermocouple and heater for antenna-coupled bolometer

This paper presents the characterization of 0.6 μm silicon-on-insulator CMOS processed integrated thermocouple-heater device for bolometer applications. Two different kinds of thermocouple with poly- and single-crystalline silicon wires have been fabricated and the performances were evaluated in terms of responsivity (Rv) and noise equivalent power (NEP). Relatively large responsivity of 336 V W−1 and small NEP of 162 pW Hz−1/2 were obtained from the electrical characterization of 100 μm long device. The high Seebeck coefficient of 346 μV K−1 and the reduced thermal conductivity of 27.3 W m−1 K−1 were obtained by the fabricated devices. Assuming the use in antenna-coupled bolometers to detect the wave at 1 THz, the thermocouple-heater device was adapted for a half-wave dipole antenna, and the performances were estimated and compared with those of other temperature sensors. Comparison revealed that the thermocouple-based bolometers showed competitive NEP and uniquely featured low power consumption.

Analysis of nonlinear characteristics of a graphene based four-terminal ballistic rectifier using a drift-diffusion model.

In this study, rectification behavior and noise spectra of a graphene based four-terminal ballistic rectifier are reported utilizing semi-classical drift-diffusion 3D modeling. The room temperature DC and RF characteristics of the novel rectifier are demonstrated considering the traps in the material similar to a real device, reducing the rectification efficiency from 0.5% to 0.35%. The responsivity and noise equivalent power of about 89.21 mV mW−1 and 97.52 pW Hz−1/2, respectively, are obtained for different frequencies varying from 50 Hz to 1 THz. Furthermore, the noise spectral analysis of the device predicts a minimum low frequency noise, which depends upon the carrier concentration inside the device active region rather than mobility, and hence enables potential applications as THz detectors for imaging.

A unipolar nano-diode detector with improved performance using the high-k material SiNx

The performance of a solid-state planar nano-diode, namely self-switching diode (SSD), is improved by depositing a 100 nm-thick SiNx film with high dielectric constant (high-k) into the insulating nano-trenches. The SiNx film grown by using plasma-enhanced chemical vapour deposition can enhance the electric field coupling over the trenches and thus increase the accumulated charges for field effect. In this case, the current–voltage nonlinearity is improved significantly and the responsivity of high-frequency rectification is also increased by a factor of almost one order up to 100 GHz. In addition, compared to the device without SiNx coating, the low frequency noise of the proposed diode is suppressed dramatically. The improved responsivity and noise-equivalent power of 11 SSDs in parallel with SiNx coating are 110 V W−1 at 50 GHz and 180 pW Hz−1/2, which are comparable to the state-of-the-art data of reported SSD arrays.