Showing papers on "Responsivity published in 2020"

A High-Performance Solution-Processed Organic Photodetector for Near-Infrared Sensing.

Abstract: Sensitive detection of near-infrared (NIR) light enables many important applications in both research and industry. Current organic photodetectors suffer from low NIR sensitivity typically due to early absorption cutoff, low responsivity, and/or large dark/noise current under bias. Herein, organic photodetectors based on a novel ultranarrow-bandgap nonfullerene acceptor, CO1-4Cl, are presented, showcasing a remarkable responsivity over 0.5 A W-1 in the NIR spectral region (920-960 nm), which is the highest among organic photodiodes. By effectively delaying the onset of the space charge limited current and suppressing the shunt leakage current, the optimized devices show a large specific detectivity around 1012 Jones for NIR spectral region up to 1010 nm, close to that of a commercial Si photodiode. The presented photodetectors can also be integrated in photoplethysmography for real-time heart-rate monitoring, suggesting its potential for practical applications.

Strain-engineered high-responsivity MoTe2 photodetector for silicon photonic integrated circuits

Abstract: In integrated photonics, specific wavelengths such as 1,550 nm are preferred due to low-loss transmission and the availability of optical gain in this spectral region. For chip-based photodetectors, two-dimensional materials bear scientifically and technologically relevant properties such as electrostatic tunability and strong light–matter interactions. However, no efficient photodetector in the telecommunication C-band has been realized with two-dimensional transition metal dichalcogenide materials due to their large optical bandgaps. Here we demonstrate a MoTe2-based photodetector featuring a strong photoresponse (responsivity 0.5 A W–1) operating at 1,550 nm in silicon photonics enabled by strain engineering the two-dimensional material. Non-planarized waveguide structures show a bandgap modulation of 0.2 eV, resulting in a large photoresponse in an otherwise photoinactive medium when unstrained. Unlike graphene-based photodetectors that rely on a gapless band structure, this photodetector shows an approximately 100-fold reduction in dark current, enabling an efficient noise-equivalent power of 90 pW Hz–0.5. Such a strain-engineered integrated photodetector provides new opportunities for integrated optoelectronic systems. A strain-induced absorption-enhanced MoTe2-based silicon photonic microring-integrated photodetector is demonstrated, featuring high responsivity of ~0.5 A W–1 at 1,550 nm, with a low noise-equivalent power of 90 pW Hz–0.5.

Mixed-dimensional PdSe2/SiNWA heterostructure based photovoltaic detectors for self-driven, broadband photodetection, infrared imaging and humidity sensing

Abstract: The new discovery of two-dimensional (2D) palladium diselenide (PdSe2) films has attracted intensive research interest due to their unique asymmetric crystal structure and extraordinary optoelectronic properties, showing great potential for broadband and polarization photodetection. Herein, we have developed for the first time a self-driven, highly polarization-sensitive, broadband photovoltaic detector based on a PdSe2/Si nanowire array (SiNWA) heterostructure. Owing to the strong light confinement effect of the SiNWA and broadband light absorption of PdSe2, the present device exhibits pronounced photovoltaic behavior and excellent performance in terms of a high responsivity of 726 mA W−1, a large specific detectivity of 3.19 × 1014 Jones, an ultrabroad spectrum response range of 0.2–4.6 μm, and a fast response speed to monitor nanosecond pulsed light signals. Significantly, an impressive polarization sensitivity of 75 is achieved for the heterostructure device, which is among the highest for 2D material-based photodetectors. Thanks to the outstanding imaging capability, the detector can record images in both near infrared (NIR) and mid-infrared (MIR) ranges with a decent resolution. Moreover, the device exhibits light-enhanced humidity sensing behavior with a high sensitivity and a fast response/recovery time. Given these remarkable device features, the PdSe2/SiNWA heterostructure will hold great promise for high-performance, polarization-sensitive broadband photodetection, infrared imaging and humidity sensing applications.

A Chiral Reduced-Dimension Perovskite for an Efficient Flexible Circularly Polarized Light Photodetector.

Abstract: Chiral quasi-2D perovskite single crystals (SCs) were investigated for their circular polarized light (CPL) detecting capability. Quasi-2D chiral perovskites, [(R)-β-MPA]2 MAPb2 I7 ((R)-β-MPA=(R)-(+)-β-methylphenethylamine, MA=methylammonium), have intrinsic chirality and the capability to distinguish different polarization states of CPL photons. Corresponding quasi-2D SCs CPL photodetector exhibit excellent detection performance. In particular, our device responsivity is almost one order of magnitude higher than the reported 2D perovskite CPL detectors to date. The crystallization dynamics of the film were modulated to facilitate its carrier transport. Parallel oriented perovskite films with a homogeneous energy landscape is crucial to maximize the carrier collection efficiency. The photodetector also exhibits superior mechanical flexibility and durability, representing a promising candidate for sensitive and robust CPL photodetectors.

Metal–Semiconductor–Metal ε-Ga2O3 Solar-Blind Photodetectors with a Record-High Responsivity Rejection Ratio and Their Gain Mechanism

Abstract: In recent years, Ga2O3 solar-blind photodetectors (SBPDs) have received great attention for their potential applications in solar-blind imaging, deep space exploration, confidential space communica...

An Electrically Modulated Single-Color/Dual-Color Imaging Photodetector.

Abstract: An electrically modulated single-/dual-color imaging photodetector with fast response speed is developed based on a small molecule (COi 8DFIC)/perovskite (CH3 NH3 PbBr3 ) hybrid film. Owing to the type-I heterojunction, the device can facilely transform dual-color images to single-color images by applying a small bias voltage. The photodetector exhibits two distinct cut-off wavelengths at ≈544 nm (visible region) and ≈920 nm (near-infrared region), respectively, without any power supply. Its two peak responsivities are 0.16 A W-1 at ≈525 nm and 0.041 A W-1 at ≈860 nm with a fast response speed (≈102 ns). Under 0.6 V bias, the photodetector can operate in a single-color mode with a peak responsivity of 0.09 A W-1 at ≈475 nm, showing a fast response speed (≈102 ns). A physical model based on band energy theory is developed to illustrate the origin of the tunable single-/dual-color photodetection. This work will stimulate new approaches for developing solution-processed multifunctional photodetectors for imaging photodetection in complex circumstances.

High-performance silicon-graphene hybrid plasmonic waveguide photodetectors beyond 1.55 μm.

Abstract: Graphene has attracted much attention for the realization of high-speed photodetection for silicon photonics over a wide wavelength range. However, the reported fast graphene photodetectors mainly operate in the 1.55 μm wavelength band. In this work, we propose and realize high-performance waveguide photodetectors based on bolometric/photoconductive effects by introducing an ultrathin wide silicon−graphene hybrid plasmonic waveguide, which enables efficient light absorption in graphene at 1.55 μm and beyond. When operating at 2 μm, the present photodetector has a responsivity of ~70 mA/W and a setup-limited 3 dB bandwidth of >20 GHz. When operating at 1.55 μm, the present photodetector also works very well with a broad 3 dB bandwidth of >40 GHz (setup-limited) and a high responsivity of ~0.4 A/W even with a low bias voltage of −0.3 V. This work paves the way for achieving high-responsivity and high-speed silicon–graphene waveguide photodetection in the near/mid-infrared ranges, which has applications in optical communications, nonlinear photonics, and on-chip sensing. The use of a silicon−graphene plasmonic waveguide has enabled the realization of fast and sensitive photodetectors that operate at the wavelength of 2 µm. In order to satisfy the demands for the applications in optical communication and optical sensing, there is the need to extend silicon photonics to wavelengths beyond 1.55 µm. However, it is a challenge to create high-performance photodetectors at these wavelengths. Now, Daoxin Dai and coworkers from Zhejiang University and Southeast University in China have proposed and realized a silicon−graphene hybrid plasmonic waveguide photodetector that operates at 2 µm with a responsivity of ~70 mA/W and a 3-dB bandwidth over 20 GHz. In this design, efficient light absorption in graphene is enabled by using a hybrid plasmonic waveguide with a wide thin silicon ridge core and a metal cap that serves as a signal electrode.

Near-infrared and visible light dual-mode organic photodetectors.

Abstract: We report a dual-mode organic photodetector (OPD) that has a trilayer visible light absorber/optical spacer/near-infrared (NIR) light absorber configuration. In the presence of NIR light, photocurrent is produced in the NIR light-absorbing layer due to the trap-assisted charge injection at the organic/cathode interface at a reverse bias. In the presence of visible light, photocurrent is produced in the visible light-absorbing layer, enabled by the trap-assisted charge injection at the anode/organic interface at a forward bias. A high responsivity of >10 A/W is obtained in both short and long wavelengths. The dual-mode OPD exhibits an NIR light response operated at a reverse bias and a visible light response operated at a forward bias, with a high specific detectivity of ~1013 Jones in both NIR and visible light ranges. A bias-switchable spectral response OPD offers an attractive option for applications in environmental pollution detection, bioimaging process, wellness, and security monitoring in two distinct bands.

Flexible and Self-Powered Photodetector Arrays Based on All-Inorganic CsPbBr3 Quantum Dots

Abstract: Flexible devices are garnering substantial interest owing to their potential for wearable and portable applications. Here, flexible and self-powered photodetector arrays based on all-inorganic perovskite quantum dots (QDs) are reported. CsBr/KBr-mediated CsPbBr3 QDs possess improved surface morphology and crystallinity with reduced defect densities, in comparison with the pristine ones. Systematic material characterizations reveal enhanced carrier transport, photoluminescence efficiency, and carrier lifetime of the CsBr/KBr-mediated CsPbBr3 QDs. Flexible photodetector arrays fabricated with an optimum CsBr/KBr treatment demonstrate a high open-circuit voltage of 1.3 V, responsivity of 10.1 A W-1 , specific detectivity of 9.35 × 1013 Jones, and on/off ratio up to ≈104 . Particularly, such performance is achieved under the self-powered operation mode. Furthermore, outstanding flexibility and electrical stability with negligible degradation after 1600 bending cycles (up to 60°) are demonstrated. More importantly, the flexible detector arrays exhibit uniform photoresponse distribution, which is of much significance for practical imaging systems, and thus promotes the practical deployment of perovskite products.

High oscillator strength interlayer excitons in two-dimensional heterostructures for mid-infrared photodetection.

Abstract: The development of infrared photodetectors is mainly limited by the choice of available materials and the intricate crystal growth process Moreover, thermally activated carriers in traditional III–V and II–VI semiconductors enforce low operating temperatures in the infrared photodetectors Here we demonstrate infrared photodetection enabled by interlayer excitons (ILEs) generated between tungsten and hafnium disulfide, WS2/HfS2 The photodetector operates at room temperature and shows an even higher performance at higher temperatures owing to the large exciton binding energy and phonon-assisted optical transition The unique band alignment in the WS2/HfS2 heterostructure allows interlayer bandgap tuning from the mid- to long-wave infrared spectrum We postulate that the sizeable charge delocalization and ILE accumulation at the interface result in a greatly enhanced oscillator strength of the ILEs and a high responsivity of the photodetector The sensitivity of ILEs to the thickness of two-dimensional materials and the external field provides an excellent platform to realize robust tunable room temperature infrared photodetectors Formation of interlayer excitons with high oscillator strength in a WS2/HfS2 heterostructure enables the realization of high-responsivity room-temperature mid- and long-wavelength infrared photodetectors

Petermann-factor sensitivity limit near an exceptional point in a Brillouin ring laser gyroscope

Abstract: Exceptional points are singularities of open systems, and among their many remarkable properties, they provide a way to enhance the responsivity of sensors. Here we show that the improved responsivity of a laser gyroscope caused by operation near an exceptional point is precisely compensated by increasing laser noise. The noise, of fundamental origin, is enhanced because the laser mode spectrum loses the oft-assumed property of orthogonality. This occurs as system eigenvectors coalesce near the exceptional point and a bi-orthogonal analysis confirms experimental observations. While the results do not preclude other possible advantages of the exceptional-point-enhanced responsivity, they do show that the fundamental sensitivity limit of the gyroscope is not improved through this form of operation. Besides being important to the physics of microcavities and non-Hermitian photonics, these results help clarify fundamental sensitivity limits in a specific class of exceptional-point sensor.

Lateral 2D WSe2 p-n Homojunction Formed by Efficient Charge-Carrier-Type Modulation for High-Performance Optoelectronics.

Abstract: As unique building blocks for next-generation optoelectronics, high-quality 2D p-n junctions based on semiconducting transition metal dichalcogenides (TMDs) have attracted wide interest, which are urgent to be exploited. Herein, a novel and facile electron doping of WSe2 by cetyltrimethyl ammonium bromide (CTAB) is achieved for the first time to form a high-quality intramolecular p-n junction with superior optoelectronic properties. Efficient manipulation of charge carrier type and density in TMDs via electron transfer between Br- in CTAB and TMDs is proposed theoretically by density functional theory (DFT) calculations. Compared with the intrinsic WSe2 photodetector, the switching light ratio (Ilight /Idark ) of the p-n junction device can be enhanced by 103 , and the temporal response is also dramatically improved. The device possesses a responsivity of 30 A W-1 , with a specific detectivity of over 1011 Jones. In addition, the mechanism of charge transfer in CTAB-doped 2D WSe2 and WS2 are investigated by designing high-performance field effect transistors. Besides the scientific insight into the effective manipulation of 2D materials by chemical doping, this work presents a promising applicable approach toward next-generation photoelectronic devices with high efficiency.

Polarization-Sensitive Self-Powered Type-II GeSe/MoS2 Van der Waals Heterojunction Photodetector

Abstract: Polarization-sensitive photodetectors are highly desirable for high-performance optical signal capture and stray light shielding in order to enhance the capability for detection and identification of targets in dark, haze, and other complex environments. Usually, filters and polarizers are utilized for conventional devices to achieve polarization-sensitive detection. Herein, to simplify the optical system, a two-dimensional self-powered polarization-sensitive photodetector is fabricated based on a stacked GeSe/MoS2 van der Waals (vdW) heterojunction which facilitates efficient separation and transportation of the photogenerated carriers because of type-II band alignment. Accordingly, a high-performance self-powered photodetector is achieved with merits of a very large on-off ratio photocurrent at zero bias of currently 104 and a high responsivity (Rλ) of 105 mA/W with an external quantum efficiency of 24.2%. Furthermore, a broad spectral photoresponse is extended from 380 to 1064 nm owing to the high absorption coefficient in a wide spectral region. One of the key benefits from these highly anisotropic orthorhombic structures of layered GeSe is self-powered polarization-sensitive detection with a peak/valley ratio of up to 2.95. This is realized irradiating with a 532 nm wavelength laser with which a maximum photoresponsivity of up to 590 mA/W is reached when the input polarization is parallel to the armchair direction. This work provides a facile route to fabricate self-powered polarization-sensitive photodetectors from GeSe/MoS2 vdW heterojunctions for integrated optoelectronic devices.

Demonstration of a Broadband Photodetector Based on a Two-Dimensional Metal-Organic Framework.

Abstract: Metal-organic frameworks (MOFs) are emerging as an appealing class of highly tailorable electrically conducting materials with potential applications in optoelectronics. Yet, the realization of their proof-of-concept devices remains a daunting challenge, attributed to their poor electrical properties. Following recent work on a semiconducting Fe3 (THT)2 (NH4 )3 (THT: 2,3,6,7,10,11-triphenylenehexathiol) 2D MOF with record-high mobility and band-like charge transport, here, an Fe3 (THT)2 (NH4 )3 MOF-based photodetector operating in photoconductive mode capable of detecting a broad wavelength range from UV to NIR (400-1575 nm) is demonstrated. The narrow IR bandgap of the active layer (≈0.45 eV) constrains the performance of the photodetector at room temperature by band-to-band thermal excitation of charge carriers. At 77 K, the device performance is significantly improved; two orders of magnitude higher voltage responsivity, lower noise equivalent power, and higher specific detectivity of 7 × 108 cm Hz1/2 W-1 are achieved under 785 nm excitation. These figures of merit are retained over the analyzed spectral region (400-1575 nm) and are commensurate to those obtained with the first demonstrations of graphene- and black-phosphorus-based photodetectors. This work demonstrates the feasibility of integrating conjugated MOFs as an active element into broadband photodetectors, thus bridging the gap between materials' synthesis and technological applications.

Tellurene Photodetector with High Gain and Wide Bandwidth.

Abstract: Two-dimensional (2D) semiconductors have been extensively explored as a new class of materials with great potential. In particular, black phosphorus (BP) has been considered to be a strong candidate for applications such as high-performance infrared photodetectors. However, the scalability of BP thin film is still a challenge, and its poor stability in the air has hampered the progress of the commercialization of BP devices. Herein, we report the use of hydrothermal-synthesized and air-stable 2D tellurene nanoflakes for broadband and ultrasensitive photodetection. The tellurene nanoflakes show high hole mobilities up to 458 cm2/V·s at ambient conditions, and the tellurene photodetector presents peak extrinsic responsivity of 383 A/W, 19.2 mA/W, and 18.9 mA/W at 520 nm, 1.55 μm, and 3.39 μm light wavelength, respectively. Because of the photogating effect, high gains up to 1.9 × 103 and 3.15 × 104 are obtained at 520 nm and 3.39 μm wavelength, respectively. At the communication wavelength of 1.55 μm, the tellurene photodetector exhibits an exceptionally high anisotropic behavior, and a large bandwidth of 37 MHz is obtained. The photodetection performance at different wavelength is further supported by the corresponding quantum molecular dynamics (QMD) simulations. Our approach has demonstrated the air-stable tellurene photodetectors that fully cover the short-wave infrared band with ultrafast photoresponse.

MoTe2 p-n Homojunctions Defined by Ferroelectric Polarization.

Abstract: Doped p-n junctions are fundamental electrical components in modern electronics and optoelectronics. Due to the development of device miniaturization, the emergence of two-dimensional (2D) materials may initiate the next technological leap toward the post-Moore era owing to their unique structures and physical properties. The purpose of fabricating 2D p-n junctions has fueled many carrier-type modulation methods, such as electrostatic doping, surface modification, and element intercalation. Here, by using the nonvolatile ferroelectric field polarized in the opposite direction, efficient carrier modulation in ambipolar molybdenum telluride (MoTe2 ) to form a p-n homojunction at the domain wall is demonstrated. The nonvolatile MoTe2 p-n junction can be converted to n-p, n-n, and p-p configurations by external gate voltage pulses. Both rectifier diodes exhibited excellent rectifying characteristics with a current on/off ratio of 5 × 105 . As a photodetector/photovoltaic, the device presents responsivity of 5 A W-1 , external quantum efficiency of 40%, specific detectivity of 3 × 1012 Jones, fast response time of 30 µs, and power conversion efficiency of 2.5% without any bias or gate voltages. The MoTe2 p-n junction presents an obvious short-wavelength infrared photoresponse at room temperature, complementing the current infrared photodetectors with the inadequacies of complementary metal-oxide-semiconductor incompatibility and cryogenic operation temperature.

A facile spray pyrolysis fabrication of Sm:CdS thin films for high-performance photodetector applications

Abstract: Achievement of high-performance photodetectors based on CdS is a key field of research and challenge in the current scenario. Here, facile fabrication and characterization of novel samarium (1, 3 and 5 wt.% Sm)-doped CdS thin films for the photodetector applications have been demonstrated. The fabricated films show good crystallinity with crystallites size ranging 18–30 nm. The morphology and homogeneity of Sm-doping ingrown films were confirmed through scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX). Field emission SEM study reveals the low dimension nanograins formation and the films are free from voids and cracks. The effects of Sm-doping on linear and nonlinear optical properties of the fabricated thin films have been elucidated. The optical parameters such as refractive index, energy gap, susceptibilities were noticed to be reduced by Sm-doping in CdS thin films. An emission peak around 536 ± 14 nm was observed in PL spectra of pure CdS which was found to be shifted and quenched by Sm-doping. Finally, the photodetector performance of the fabricated thin films has been investigated for 532 nm laser light. The photodetector based on the 1 wt.% Sm:CdS shows an improved performance (higher responsivity of 1.01 AW−1, higher detectivity of 2.21 × 1012 Jones, excellent photosensitivity of ∼4.9 × 103, and very high external quantum efficiency (EQE) of 257 %) compared to pure CdS (responsivity of 0.213 AW−1, detectivity of 7.43 × 1011 Jones, photosensitivity of ∼2.0 × 103, and EQE of 249.70 %). These results propose a much simpler route to achieve high-quality CdS films for photodetector applications.

Flexible Ultrathin Single-Crystalline Perovskite Photodetector.

Abstract: Flexible optoelectronic devices attract considerable attention due to their prominent role in creating novel wearable apparatus for bionics, robotics, health care, and so forth. Although bulk single-crystalline perovskite-based materials are well-recognized for the high photoelectric conversion efficiency than the polycrystalline ones, their stiff and brittle nature unfortunately prohibits their application for flexible devices. Here, we introduce ultrathin single-crystalline perovskite film as the active layer and demonstrate a high-performance flexible photodetector with prevailing bending reliability. With a much-reduced thickness of 20 nm, the photodetector made of this ultrathin film can achieve a significantly increased responsivity as 5600A/W, 2 orders of magnitude higher than that of recently reported flexible perovskite photodetectors. The demonstrated 0.2 MHz 3 dB bandwidth further paves the way for high-speed photodetection. Notably, all its optoelectronic characteristics resume after being bent over thousands of times. These results manifest the great potential of single-crystalline perovskite ultrathin films for developing wearable and flexible optoelectronic devices.

Zero-bias mid-infrared graphene photodetectors with bulk photoresponse and calibration-free polarization detection

Abstract: Bulk photovoltaic effect (BPVE), featuring polarization-dependent uniform photoresponse at zero external bias, holds potential for exceeding the Shockley-Queisser limit in the efficiency of existing opto-electronic devices. However, the implementation of BPVE has been limited to the naturally existing materials with broken inversion symmetry, such as ferroelectrics, which suffer low efficiencies. Here, we propose metasurface-mediated graphene photodetectors with cascaded polarization-sensitive photoresponse under uniform illumination, mimicking an artificial BPVE. With the assistance of non-centrosymmetric metallic nanoantennas, the hot photocarriers in graphene gain a momentum upon their excitation and form a shift current which is nonlocal and directional. Thereafter, we demonstrate zero-bias uncooled mid-infrared photodetectors with three orders higher responsivity than conventional BPVE and a noise equivalent power of 0.12 nW Hz−1/2. Besides, we observe a vectorial photoresponse which allows us to detect the polarization angle of incident light with a single device. Our strategy opens up alternative possibilities for scalable, low-cost, multifunctional infrared photodetectors. Here, graphene-based plasmonic metamaterials are used to generate an artificial bulk photovoltaic effect, enabling the realization of mid-infrared photodetectors with enhanced responsivity and calibration-free polarization detection at room temperature.

A self-powered solar-blind photodetector with large Voc enhancing performance based on the PEDOT:PSS/Ga2O3 organic–inorganic hybrid heterojunction

Abstract: Self-powered photodetectors that can convert suitable light into an electrical signal without power supply are important and fundamental building blocks in the wide applications of environmental monitoring, light-wave communication, territory intrusions, and imaging technology. Motivated by the goals of fabricating a good-reliability, high-efficiency, and cost-efficient self-powered photodetector realizing zero power consumption, we construct an organic–inorganic hybrid photodetector with large open-circuit voltage (Voc ≈ 0.9 V) based on the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/Ga2O3 heterojunction. The prepared hybrid photodetector demonstrates a prominent self-powered photodetection performance with fantastic responsivity of 37.4 mA W−1, superior detectivity of 9.2 × 1012 Jones, and high external quantum efficiency of 18.3% at zero bias with 254 nm light illumination of 0.3 μW cm−2. Under excitation of the 248 nm pulsed laser, the photodetector shows an ultrafast response speed with a rise time of 3.3 μs and decay time of 71.2 μs. Furthermore, the hybrid photodetector displays specific solar-blind spectrum selectivity with a high R250nm/R360nm rejection ratio of 7 × 103 and good stability in ambient air even after one-week storage. The excellent photoelectric performance of the hybrid self-powered photodetector mainly profits from the efficient separation of photogenerated electron–hole pairs driven by the built-in electric field and the large photovoltaic effect (Voc ≈ 0.9 V) of the PEDOT:PSS/Ga2O3 heterojunction. With the ability of harvesting photon energy from deep space to support the operation, this low-cost and high-performance self-powered photodetector will open potential applications in space exploration.

Bionic Detectors Based on Low-Bandgap Inorganic Perovskite for Selective NIR-I Photon Detection and Imaging.

Abstract: Fluorescence imaging with photodetectors (PDs) toward near-infrared I (NIR-I) photons (700-900 nm), the so-called "optical window" in organisms, has provided an important path for tracing biological processes in vivo. With both excitation photons and fluorescence photons in this narrow range, a stringent requirement arises that the fluorescence signal should be efficiently differentiated for effective sensing, which cannot be fulfilled by common PDs with a broadband response such as Si-based PDs. In this work, delicate optical microcavities are designed to develop a series of bionic PDs with selective response to NIR-I photons, the merits of a narrowband response with a full width at half maximum (FWHM) of <50 nm, and tunability to cover the NIR-I range are highlighted. Inorganic halide perovskite CsPb0.5 Sn0.5 I3 is chosen as the photoactive layer with comprehensive bandgap and film engineering. As a result, these bionic PDs offer a signal/noise ratio of ≈106 , a large bandwidth of 543 kHz and an ultralow detection limit of 0.33 nW. Meanwhile, the peak responsivity (R) and detectivity (D*) reach up to 270 mA W-1 and 5.4 × 1014 Jones, respectively. Finally, proof-of-concept NIR-I imaging using the PDs is demonstrated to show great promise in real-life application.

WS2 Nanosheet/Graphene Heterostructures for Paper-Based Flexible Photodetectors

Abstract: We report a low-cost and green synthesis approach to produce high-performance optoelectronics based on WS2-decorated pencil trace on ordinary cellulose paper It is noteworthy that the photodetector was prepared via simply nontoxic solution-processed WS2 nanosheets, pencil-drawn graphene conducting films, and biodegradable papers Portable and flexible electronics based on WS2/graphene show excellent photoresponse in a broad spectral region from visible to near IR because of plasmonic improvement and efficient photoabsorption Liquid-phase-exfoliated atomically thin WS2 nanosheets were decorated on a conducting film of pencil trace using the large area electrophoretic deposition technique The photodetector based on the WS2/graphene heterostructure shows excellent temporal photoresponse with a responsivity of 0439 A/W, a detectivity of 141 × 1010 Jones, and an external quantum efficiency of 8139% The high-performance photodetector shows piezoresistive modulation in electric transport The device response was investigated up to 500 bending cycles Finally, the present finding advocates the great development over previously reported nonbiodegradable and small-area optoelectronic devices

A mixed-dimensional 1D Se–2D InSe van der Waals heterojunction for high responsivity self-powered photodetectors

Abstract: Mixed-dimension van der Waals (vdW) p-n heterojunction photodiodes have inspired worldwide efforts to combine the excellent properties of 2D materials and traditional semiconductors without consideration of lattice mismatch. However, owing to the scarcity of intrinsic p-type semiconductors and insufficient optical absorption of the few layer 2D materials, a high performance photovoltaic device based on a vdW heterojunction is still lacking. Here, a novel mixed-dimension vdW heterojunction consisting of 1D p-type Se nanotubes and a 2D flexible n-type InSe nanosheet is proposed by a facile method, and the device shows excellent photovoltaic characteristics. Due to the superior properties of the hybrid p-n junction, the mix-dimensional van der Waals heterojunction exhibited high on/off ratios (103) at a relatively weak light intensity of 3 mW cm-2. And a broadband self-powered photodetector ranging from the UV to visible region is achieved. The highest responsivity of the device could reach up to 110 mA W-1 without an external energy supply. This value is comparable to that of the pristine Se device at 5 V and InSe device at 0.1 V, respectively. Furthermore, the response speed is enhanced by one order of magnitude over the single Se or InSe device even at a bias voltage. This work paves a new way for the further development of high performance, low cost, and energy-efficient photodetectors by using mixed-dimensional vdW heterostructures.

An ultrahigh responsivity self-powered solar-blind photodetector based on a centimeter-sized β-Ga2O3/polyaniline heterojunction.

Abstract: Wide band gap semiconductors are promising UV photodetector materials due to their suitable bandgap, high crystal quality, strong absorption and large carrier mobility. Up to now, deep UV photodetectors are mainly based on epitaxial thin films, which have some undesired properties such as p-type doping difficulty. Lattice mismatch hinders the further development of these devices. Here, a high performance self-powered solar-blind UV photodetector was realized by a facile combination of a centimeter-sized single crystal β-Ga2O3 microwire and polyaniline. Owing to the excellent organic/inorganic hybrid p–n junction, the device shows an ultrahigh responsivity of 21 mA W−1 at 246 nm with a sharp cut-off wavelength of 272 nm without an external power supply. Moreover, the dark current is 0.08 pA, which is smaller than those of almost all the previous metallic oxide based solar-blind UV photodetectors. The photodetector also shows a high UV/visible rejection ratio (102) at zero bias voltage. Finally, a physical model of the self-powered photodetector is also proposed. This work provides a simple, low-cost, and effective method for preparing high performance self-powered solar-blind UV photodetectors based on organic/inorganic heterojunctions.

Photogating WS2 Photodetectors Using Embedded WSe2 Charge Puddles

Abstract: Performance of 2D photodetectors is often predominated by charge traps that offer an effective photogating effect. The device features an ultrahigh gain and responsivity, but at the cost of a retar...

Detector-Only Spectrometer Based on Structurally Colored Silicon Nanowires and a Reconstruction Algorithm.

Abstract: Spectroscopy is a cornerstone in the field of optics. Conventional spectrometers generally require two elements. The first provides wavelength selectivity, for example, diffraction grating or Michelson interferometer. The second is a detector (or detector array). Many applications would benefit from very small and lightweight spectrometers. This motivates us to investigate what may be regarded as an ultimate level of miniaturization for a spectrometer, in which it consists solely of a detector array. We demonstrate a chip containing 24 pixels, each comprising a silicon nanowire (Si NW) array photodetector formed above a planar photodetector. The NWs are structurally colored, enabling us to engineer the responsivity spectra of all photodetectors in the chip. Each pixel thus combines wavelength selectivity and photodetection functions. We demonstrate the use of our chip to reconstruct the spectrum of an unknown light source impinging upon it. This is achieved by an algorithm that takes as its inputs the measured photocurrents from the pixels and a library of their responsivity spectra.

Waveguide-integrated van der Waals heterostructure photodetector at telecom wavelengths with high speed and high responsivity.

Abstract: Intensive efforts have been devoted to the exploration of new optoelectronic devices based on two-dimensional transition-metal dichalcogenides (TMDCs) owing to their strong light–matter interaction and distinctive material properties. In particular, photodetectors featuring both high-speed and high-responsivity performance are of great interest for a vast number of applications such as high-data-rate interconnects operated at standardized telecom wavelengths. Yet, the intrinsically small carrier mobilities of TMDCs become a bottleneck for high-speed application use. Here, we present high-performance vertical van der Waals heterostructure-based photodetectors integrated on a silicon photonics platform. Our vertical MoTe2–graphene heterostructure design minimizes the carrier transit path length in TMDCs and enables a record-high measured bandwidth of at least 24 GHz under a moderate bias voltage of –3 V. Applying a higher bias or employing thinner MoTe2 flakes boosts the bandwidth even to 50 GHz. Simultaneously, our device reaches a high external responsivity of 0.2 A W–1 for incident light at 1,300 nm, benefiting from the integrated waveguide design. Our studies shed light on performance trade-offs and present design guidelines for fast and efficient devices. The combination of two-diemensional heterostructures and integrated guided-wave nano photonics defines an attractive platform to realize high-performance optoelectronic devices, such as photodetectors, light-emitting devices and electro-optic modulators. The low carrier mobilities of TMDCs pose a challenge for applications in high-speed photodetection. Integrating vertical two-dimensional heterostructures with photonic waveguides allows the intrinsic speed limitations to be overcome and record-high photodetection bandwidths to be achieved.

Anisotropic ultrasensitive PdTe2-based phototransistor for room-temperature long-wavelength detection.

Abstract: Emergent topological Dirac semimetals afford fresh pathways for optoelectronics, although device implementation has been elusive to date. Specifically, palladium ditelluride (PdTe2) combines the capabilities provided by its peculiar band structure, with topologically protected electronic states, with advantages related to the occurrence of high-mobility charge carriers and ambient stability. Here, we demonstrate large photogalvanic effects with high anisotropy at terahertz frequency in PdTe2-based devices. A responsivity of 10 A/W and a noise-equivalent power lower than 2 pW/Hz0.5 are achieved at room temperature, validating the suitability of PdTe2-based devices for applications in photosensing, polarization-sensitive detection, and large-area fast imaging. Our findings open opportunities for exploring uncooled and sensitive photoelectronic devices based on topological semimetals, especially in the highly pursuit terahertz band.