Extreme Sensitivity of Room-Temperature Photoelectric Effect for Terahertz Detection

Enhanced room-temperature terahertz detection and imaging derived from anti-reflection 2D perovskite layer on MAPbI3 single crystals

Terahertz (THz) detection technology is getting increasing attention from scientists and industries alike due to its superiority in imaging, communication, and defense. Unfortunately, the detection of THz electromagnetic waves under room temperature requires a complicated device architecture design or additional cryogenic cooling units, which increase the cost and complexity of devices, subsequently imposing an impediment in its universal application. In this work, THz detectors operated under room temperature are designed based on the thermoelectric effect with MAPbI₃ single crystals (SCs) as active layers. With solution-processed molecular growth engineering, the anti-reflection 2D perovskite layers were constructed on SCs' surfaces to suppress THz reflection loss. Simultaneously, by finely regulating the main carrier types and the direction of the applied bias across the inclined energy level, the thermoelectric effect is further promoted. As a result, THz-induced ΔT in MAPbI₃ SCs reaches 4.6 °C, while the enhancement in the bolometric and photothermoelectric effects reach ∼4.8 times and ∼16.9 times, respectively. Finally, the devices achieve responsivity of 88.8 μA W^-1 at 0.1 THz under 60 V cm^-1, noise equivalent power (NEP) less than 2.16 × 10^-9 W Hz^-1/2, and specific detectivity (D*) of 1.5 × 10⁸ Jones, which even surpasses the performance of state-of-the-art graphene-based room-temperature THz thermoelectric devices. More importantly, proof-of-concept imaging gives direct evidence of perovskite-based THz sensing in practical applications.

Optically Transparent Broadband Microwave Absorber by Graphene and Metallic Rings

The demand for optically transparent microwave absorbers has attracted increasing interest among researchers in recent years. However, integrating broadband microwave absorption and high optical transparency remains a challenge. This report demonstrates a scheme for broadband microwave absorbers, featuring a 90% absorption bandwidth of 10 GHz covering a frequency range of 25.2-35.2 GHz and high compatibility with good optical transparency in a wide band from the visible to infrared. The absorber is based on a Jaumann structure composed of two graphene sheets sandwiched by dielectric and backed by an arrayed-metallic-rings sheet. Guided by derived formulas, this absorber exhibits complete absorption if the sheet resistance of graphene is close to 500 Ω sq^-1. The bandwidth and center frequency of the absorption spectra can be readily tuned simply via changes in the thickness of the dielectric between the graphene films and arrayed-metallic-rings sheet. Moreover, the absorber is insensitive to the incident angle of radiation and can achieve broadband and near-unity absorption even at oblique incidence. The graphene-based absorber proposed herein provides a viable solution for effectively integrating broadband and near-unity microwave absorption with high optical transparency, thereby enabling widespread applications in optics, communications, and solar cells.

Quantum emitters and detectors based on 2D van der Waals materials

Light plays an essential role in our world, with several technologies relying on it. Photons will also play an important role in the emerging quantum technologies, which are primed to have a transformative effect on our society. The development of single-photon sources and ultra-sensitive photon detectors is crucial. Solid-state emitters are being heavily pursued for developing truly single-photon sources for scalable technology. On the detectors' side, the main challenge lies in inventing sensitive detectors operating at sub-optical frequencies. This review highlights the promising research being conducted for the development of quantum emitters and detectors based on two-dimensional van der Waals (2D-vdW) materials. Several 2D-vdW materials, from canonical graphene to transition metal dichalcogenides and their heterostructures, have generated a lot of excitement due to their tunable emission and detection properties. The recent developments in the creation, fabrication and control of quantum emitters hosted by 2D-vdW materials and their potential applications in integrated photonic devices are discussed. Furthermore, the progress in enhancing the photon-counting potential of 2D material-based detectors, viz. 2D photodetectors, bolometers and superconducting single-photon detectors functioning at various wavelengths is also reported.

High Performance of Room-Temperature NbSe2 Terahertz Photoelectric Detector

Photoelectric detection is developing rapidly from ultraviolet to infrared band. However, terahertz (THz) photodetection approaches is constrained by the bandgap, dark current, and absorption ability. In this work, room-temperature photoelectric detection is extended to the THz range implemented in a planar metal-NbSe₂-metal structure based on an electromagnetic induced well (EIW) theory, exhibiting an excellent broadband responsivity of 5.2 × 10⁷ V W^-1 at 0.027 THz, 7.8 × 10⁶ V W^-1 at 0.173 THz, and 9.6 × 10⁵ V W^-1 at 0.259 THz. Simultaneously, the NbSe₂ photoelectric detector (PD) with ultrafast response speed (∼610 ns) and ultralow equivalent noise power (4.6 × 10^-14 W Hz^-1/2) in the THz region is realized, enabling high-resolution imaging. The figure of merit (FOM) characterizing the detection performance of the device is 2 orders of magnitude superior to that of the reported THz PDs based 2D materials. Furthermore, the THz response speed is 2 orders of magnitude faster than that of the visible due to the different response mechanisms of the device. Our results exhibit promising potential to achieve highly sensitive and ultrafast photoelectric detection.

Ultrabroadband Tellurium Photoelectric Detector from Visible to Millimeter Wave

Ultrabroadband photodetection is of great significance in numerous cutting-edge technologies including imaging, communications, and medicine. However, since photon detectors are selective in wavelength and thermal detectors are slow in response, developing high performance and ultrabroadband photodetectors is extremely difficult. Herein, one demonstrates an ultrabroadband photoelectric detector covering visible, infrared, terahertz, and millimeter wave simultaneously based on single metal-Te-metal structure. Through the two kinds of photoelectric effect synergy of photoexcited electron-hole pairs and electromagnetic induced well effect, the detector achieves the responsivities of 0.793 A W^-1 at 635 nm, 9.38 A W^-1 at 1550 nm, 9.83 A W^-1 at 0.305 THz, 24.8 A W^-1 at 0.250 THz, 87.8 A W^-1 at 0.172 THz, and 986 A W^-1 at 0.022 THz, respectively. It also exhibits excellent polarization detection with a dichroic ratio of 468. The excellent performance of the detector is further verified by high-resolution imaging experiments. Finally, the high stability of the detector is tested by long-term deposition in air and high-temperature aging. The strategy provides a recipe to achieve ultrabroadband photodetection with high sensitivity and fast response utilizing full photoelectric effect.

Photodetectors of 2D Materials from Ultraviolet to Terahertz Waves

2D materials are considered to be the most promising materials for photodetectors due to their unique optical and electrical properties. Since the discovery of graphene, many photodetectors based on 2D materials have been reported. However, the low quantum efficiency, large noise, and slow response caused by the thinness of 2D materials limit their application in photodetectors. Here, recent progress on 2D material photodetectors is reviewed, covering the spectrum from ultraviolet to terahertz waves. First the interaction of 2D materials with light is analyzed in terms of optical physics. Then the present methods to improve the performance of 2D material photodetectors are summarized, such as defect engineering, p-n junctions and hybrid detectors, and the issue of serious overestimation of the performance in reported photodetectors based on 2D materials is discussed. Next, a comparison of 2D material photodetectors with traditional commercially available detectors shows that it is difficult to balance the current 2D material photodetectors with regard to having simultaneously both high sensitivity and fast response. Finally, a possible novel EIW mechanism is suggested to advance the performance of 2D material photodetectors in the future.

Ultrabroadband, Ultraviolet to Terahertz, and High Sensitivity CH3NH3PbI3 Perovskite Photodetectors

Owning to the unique optical and electronic properties, organic-inorganic hybrid perovskites have made impressive progress in photodetection applications. However, achieving ultrabroadband detection over the ultraviolet (UV) to terahertz (THz) range remains a major challenge for perovskite photodetectors. Here, we report an ultrabroadband (UV-THz) dual-mechanism photodetector based on CH₃NH₃PbI₃ films. The photoresponse of the PD in the UV-visible (vis) and near-infrared (NIR)-THz bands is mainly caused by the photoconductive (PC) effect and bolometric effect, respectively. High responsivities ranging from 10⁵ to 10² mA W^-1 are acquired within UV-THz bands under 1 V bias voltage at room temperature. Moreover, the device also shows fast rise and decay times of 76 and 126 ns under 1064 nm laser illumination, respectively. This work provides insight into the thermoelectric characteristics of perovskite and offers a new way to realize ultrabroadband photodetectors notably for THz detector at room temperature.