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A catalyst (ZIS/Ag@CN) with the ultra-close Van der Waals contact and silver single-atom bridge has been designed for photocatalytic water splitting. [Display omitted] The construction of ultra-close 2D atomic-thickness Van der Waals heterojunctions with high-speed charge transfer still faces challenges. Here, we synthesized single-layer ZnIn 2 S 4 and g-C 3 N 4 , and introduced silver single atoms to regulate Van der Waals heterojunctions at the atomic level to optimize charge transfer and catalytic activity. At the atomic scale, the impact of detailed structural differences between the two characteristic surfaces of ZnIn 2 S 4 ([Zn-S 4 ] and [In-S 4 ]) on catalytic performance has been first proposed. Experiments combined with the DFT study demonstrate that single atom Ag not only acts as a charge transfer bridge but also regulates the energy band and intrinsic catalytic activity. Benefiting from the enhanced electron delocalization, the synthesized catalyst ZIS/Ag@CN exhibits excellent photocatalytic performance, with a hydrogen production rate of 5.50 mmol·g−1·h−1, which is much higher than the reported Ag-based single-atom catalysts so far. This work provides a new understanding of atomic-level heterojunction interface regulation and modification. [ABSTRACT FROM AUTHOR]

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Incorporating atomically thin 2D semiconductors (2DSCs) into the vertical complementary field‐effect transistors (CFETs) is of great significance in enabling devices to break through the sub‐nanometer scaling limit. However, due to the lack of effective doping technology and the difficult‐to‐control electrode interface, simultaneously realizing high‐performance p‐type and n‐type devices using a single metal electrode presents great challenges for 2D‐CFETs design. In this study, an innovative electrical contact strategy is proposed by constructing van der Waals heterojunction (vdWH) using 2DSCs to regulate the electrical contact properties between the metal electrode and 2DSC channel. First‐principles calculations reveal that degenerate or quasi‐degenerate complementary doping is achieved in a series of transition metal dichalcogenides (TMDs) by designing (quasi‐)broken‐gap vdWHs and utilizing their interlayer charge transfer. Metal‐2DSC contact barriers can be effectively regulated by introducing 2DSC intercalation and constructing vdWH. P‐type (quasi‐)Ohmic contacts are realized between Au electrode and various TMD channels, as well as between WTe2 channel and different metal electrodes. Moreover, quantum transport simulations present the remarkable on‐current over 102 µA µm−1 in both p‐type and n‐type 2D‐FETs by employing the vdWH and metal‐vdWH electrodes. The proposed vdWH strategy is applicable to various metal‐2DSC contacts and will shed light on future high‐performance 2D‐CFET integrations. [ABSTRACT FROM AUTHOR]

2D materials hold potential for developing low‐cost, high‐performance broadband polarized infrared photodetectors. However, the development of 2D broadband polarized infrared photodetectors is largely constrained by the fixed bandgap spectral (cutoff wavelength) limitations of available semiconductors. Here, an approach is presented that leverages anisotropic interlayer excitons (IEXs) within a type‐II van der Waals heterojunction, achieving polarization photoresponse beyond the intrinsic bandgap spectral limits of its constituent semiconductors. By constructing heterojunctions using CrPS4 and ReS2, a unique type‐II band alignment, enabling strong anisotropic optical excitation is achieved through the interlayer sub‐bandgap, which is lower than the intrinsic bandgaps of both CrPS4 and ReS2. The heterojunction exhibits a responsivity of 0.3 A W−1 and a polarization ratio of 1.3 at an incident photon energy of 0.8 eV, comparable to naturally anisotropic materials with intrinsic bandgaps. Additionally, the potential of anisotropic IEXs is demonstrated for dual‐band polarization detection by introducing a ReS2/CrPS4/MoS2 heterojunctions with distinct inte rlayer sub‐bandgaps. This flexible design of IEXs offers a new platform for multi‐dimensional optical sensing and on‐chip optoelectronic applications. [ABSTRACT FROM AUTHOR]

Multi-spectral detection had significant applications in many fields of industry. High-performance broadband photodetectors integrating multi-band responses became one of the important research directions of optical imaging technology. Current research progress of broadband photodetectors was briefly introduced. The prospects of 2-D/3-D mix-dimensional van der Waals (VDW) heterojunctions in the development of broadband photodetectors were elaborated. Some progress of broadband phototransistors based on 2-D transition metal dichalcogenides/3-D group IV materials VDW heterojunctions by the research group, including traditional NPN-type, PNP-type phototransistors and emerging phototransistors with Schottky junction collectors were reviewed. Ultimately, the applications of these phototransistors were prospected. [ABSTRACT FROM AUTHOR]

Photodetectors with good polarization detection ability are promising in many applications, such as remote sensing imaging and environmental monitoring. However, the traditional polarization detection systems fall short in meeting integration demands of the integrated‐circuits field due to additional optical elements. The emerging 2D materials with in‐plane anisotropic structures provide a possible method to fabricate remarkable polarization detectors. Modulating the band structure by gate voltage is an important strategy for developing optoelectronic devices. Herein, a polarized photodetector based on PdSe2/MoS2 out‐of‐plane heterojunction is fabricated. Due to its unique out‐of‐plane heterostructure, the device exhibits excellent photoresponse characteristics and polarization sensitivity, including an excellent responsivity of 10.19A/W, an extremely high external quantum efficiency of 2429%, a fast rise/decay time of 68/192 µs, and a high photocurrent anisotropy ratio of 3.09. Based on the adjustment of the built‐in electric field through gate voltage, the performance of the device can be accordingly modulated. As the gate voltage increases from −30 to 30 V, the responsivity gradually increases from 7.5 to 13A/W and the detectivity increases from 1.53 to 2.63 × 109Jones. Finally, its olarization imaging ability is demonstrated at different polarization angles. The findings indicate that PdSe2/MoS2 devices exhibit significant potential for polarized photoelectric detection. [ABSTRACT FROM AUTHOR]

Single‐photon detectors (SPDs) are crucial in applications ranging from space, biological imaging to quantum communication and information processing. The SPDs that operate at room temperature are of particular interest to broader application space as the energy overhead introduced by cryogenic cooling can be avoided. Although silicon‐based single photon avalanche diodes (SPADs) are well‐matured and operate at room temperature, the bandgap limitation restricts their operation at telecommunication wavelength (1550 nm) and beyond. InGaAs‐based SPADs, on the other hand, are sensitive to 1550 nm photons but suffer from relatively lower efficiency, high dark count rate, afterpulsing probability, and pose hazards to the environment from the fabrication process. In this work, the properties of nanomaterials that can be leveraged to address these challenges are demonstrated and a room‐temperature single‐photon detector capable of operating at 1550 nm is realized. This is achieved by coupling a low bandgap (≈ 350 meV) absorber (black phosphorus) to a sensitive van der Waals probe that is capable of detecting discrete electron fluctuation. The device is optimized for operation at 1550 nm and demonstrates an overall quantum efficiency of 21.4% (estimated as 42.8% for polarized light), and a minimum dark count of ≈ 720 Hz at room temperature. [ABSTRACT FROM AUTHOR]

Single‐molecule diode was the first proposed device in molecular electronics. Despite the great efforts and advances over 50 years, the reported rectification ratios, the most critical parameter of a diode, remain moderate for the single‐molecule diode. Herein, we report an approach to achieve a larger rectification ratio by adopting the combined strategies of p‐type boron doping, the single‐layer graphene nodes, and the van der Waals layer‐by‐layer architecture. Measured current–voltage curves showed one of the as‐fabricated single‐molecule diodes hit an unprecedented large rectification ratio of 457 at ±1 V. Break junction operations and spectroscopic measurements revealed the three‐atom‐thick configuration of the single‐molecule diodes. With the experimental and theoretical calculation results, we demonstrated the doped boron atoms induced holes to redistribute the electron density, making the asymmetric coupling at positive and negative biases, and the van der Waals interaction promoted asymmetric coupling and significantly boosted diode performance. [ABSTRACT FROM AUTHOR]

2D van der Waal (vdWs) heterostructures present unique optoelectronic characteristics, making them favorable layer structures for constructing promising optoelectronic devices with multifunctional applications. Nevertheless, as a result of significant interface recombination of the photogenerated electron‐hole pairs and the presence of various absorption edges within constituent layers, they are prone to experiencing low carrier collection efficiency. In this work, a combined theoretical and experimental investigation are presented on the In2Se3/ReS2 vdWs heterostructure, aimed at developing high‐performance and broadband photodetector with multifunctionalities. In theoretical investigations, it is observed that, by adjusting the polarization states (+P to −P) in the In2Se3 layer, band alignment can be effectively tuned from type‐I to type‐II, providing a narrow bandgap of ≈0.65 eV, which is beyond that of their individual constituents. As a photodetector, the device shows broadband photoresponse ranging from 532 to 1550 nm with ultrahigh responsivity (99.36 AW−1), detectivity (3.5 × 1013 Jones), and external quantum efficiency (34195%). Additionally, competitive polarization sensitivity across the broad spectrum and imagining capability are observed with In2Se3/ReS2 vdWs heterostructure. This study demonstrates that In2Se3/ReS2 vdWs heterostructure device provides a promising technique for developing high‐performance 2D optoelectronic devices with multifunctionalities. [ABSTRACT FROM AUTHOR]

Fabricating heterojunctions with precisely controlled interfacial structures is crucial for exploring novel low-dimensional physics and for realizing high-performance devices. However, such capabilities are often constrained by contamination from the ambient environment or by the limitations of applicable methods and materials under vacuum conditions. In this study, MoS2/Au(111) heterostructures were fabricated by exfoliating MoS2 thin layers onto a crystallized Au(111) surface using a gold-assisted exfoliation method in an ultra-high vacuum environment. This method yields millimeter-sized monolayer or sub-millimeter-sized bilayers with contamination-free interfaces, which are unattainable for samples made in air. Scanning tunneling microscopy revealed that both the monolayer and the bilayer exhibit uniform and well-ordered moiré superlattices controlled by the twisting angle between the Au(111) surface and the MoS2 overlayer. The direct contact with the Au surface renders the monolayer MoS2 weakly metallic, while a less coupled bilayer is semiconducting, indicating a 0.54 eV Schottky barrier for the MoS2/Au(111) contact. This method is applicable to various combinations of van der Waals materials and metal surfaces. The uniform and controllable heterojunctions can serve as ideal model systems for exploring semiconductor–metal interfaces and atomic structures formed within.

Highlights Recent progress on the applications of 2D materials in perovskite solar cells is discussed from the views of bottom interfaces, top interfaces, and electrodes. The roles of van der Waals heterojunction in enhancing the performance of perovskite solar cells are highlighted. The future directions and challenges in development of 2D materials-based perovskite solar cells are provided.

Highlights: Recent progress on the applications of 2D materials in perovskite solar cells is discussed from the views of bottom interfaces, top interfaces, and electrodes. The roles of van der Waals heterojunction in enhancing the performance of perovskite solar cells are highlighted. The future directions and challenges in development of 2D materials-based perovskite solar cells are provided. Perovskite solar cells (PSCs) offer low costs and high power conversion efficiency. However, the lack of long-term stability, primarily stemming from the interfacial defects and the susceptible metal electrodes, hinders their practical application. In the past few years, two-dimensional (2D) materials (e.g., graphene and its derivatives, transitional metal dichalcogenides, MXenes, and black phosphorus) have been identified as a promising solution to solving these problems because of their dangling bond-free surfaces, layer-dependent electronic band structures, tunable functional groups, and inherent compactness. Here, recent progress of 2D material toward efficient and stable PSCs is summarized, including its role as both interface materials and electrodes. We discuss their beneficial effects on perovskite growth, energy level alignment, defect passivation, as well as blocking external stimulus. In particular, the unique properties of 2D materials to form van der Waals heterojunction at the bottom interface are emphasized. Finally, perspectives on the further development of PSCs using 2D materials are provided, such as designing high-quality van der Waals heterojunction, enhancing the uniformity and coverage of 2D nanosheets, and developing new 2D materials-based electrodes. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2D/2D Van der Waals (VDW) heterojunction between BCN/CuPc. • Phosphate group insertion between copper phthalocyanine (CuPc) and B-doped and N -deficient g-C 3 N 4 (BDCNN) to design and construct a Van der Waals heterojunction. • Phosphate group as a charge modulator and an efficient conduit for charge transfer. • Interfacial interaction charge transfer mechanism. The realization of 2D/2D Van der Waals (VDW) heterojunctions represents an advanced approach to achieving superior photocatalytic efficiency. However, electron transfer through Van der Waals heterojunctions formed via ex-situ assembly encounters significant challenges at the interface due to contrasting morphologies and potential barriers among the nanocomposite substituents. Herein, a novel approach is presented, involving the insertion of a phosphate group between copper phthalocyanine (CuPc) and B-doped and N -deficient g-C 3 N 4 (BDCNN), to design and construct a Van der Waals heterojunction labeled as xCu[acs]/yP-BDCNN. The introduction of phosphate as a charge modulator and efficient conduit for charge transfer within the heterojunction resulted in the elimination of spatial barriers and induced electron movement from BDCNN to CuPc in the excited states. Consequently, the catalytic central Cu2+ in CuPc captured the photoelectrons, leading to the conversion of CO 2 to C 2 H 4 , CO and CH 4. Remarkably, this approach resulted in a 78-fold enhancement in photocatalytic efficiency compared to pure BDCNN. Moreover the findings confirm that the 2D-2D 4Cu[acs]/9P-BDCNN sheet-like heterojunction effectively boosts photocatalytic activity for persistent pollutants such as methyl orange (MO), methylene blue (MB), rhodamine B (RhB), and tetracycline antibiotics (TCs). The introduction of "interfacial interacting" substances to establish an electron transfer pathway presents a novel and effective strategy for designing photocatalysts capable of efficiently reducing CO 2 into valuable products. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) self‐powered photodetectors have attracted considerable attention due to their exceptional sensitivity, and low dark current. However, the poor responsivity of single heterojunctions with type‐III band alignment is primarily attributed to band‐to‐band tunneling. The implementation of a double heterojunction has the potential to enhance photovoltaic responsivity, enable broadband detection, and improve response speed. In this study, a back‐to‐back type‐III band alignment based on SnSe2/Bi2Se3/MoTe2 double heterostructure by dry transfer method is designed. As a result, it exhibited an impressive photovoltaic performance in the overlapping region. Achieving a maximum responsivity (R), external quantum efficiency (EQE), photoelectric conversion efficiency (PCE), and specific detectiviy (D*) of 493 mA W−1, 76 %, 3 % and 1.8 × 1011 Jones at a gate voltage (Vg) of 60 V under 808 nm illumination. It can be ascribed to the effective depletion region at the SnSe2/Bi2Se3 interface and the reversed band edge from depletion to accumulation mode at Bi2Se3/MoTe2 interface. In addition, a faster response speed of 553/583 µs and a lower dark current of 2.9 pA can be obtained. Moreover, this double heterostructure achieves better photovoltaic performance with Vg compared to the single MoTe2/SnSe2 heterojunction. These results demonstrates the potential as a candidate for back‐to‐back type‐III band alignment in low power optoelectronics. [ABSTRACT FROM AUTHOR]

Resistive random access memory (RRAM) crossbar arrays require the highly nonlinear selector with high current density to address a specific memory cell and suppress leakage current through the unselected cell. 3D monolithic integration of RRAM array requires selector devices with a small footprint and low‐temperature processing for ultrahigh‐density data storage. Here, an ultrathin two‐terminal n‐p‐n selector with 2D transition metal dichalcogenides (TMDs) is designed by a low‐temperature transfer method. The van der Waals contact between transferred Au electrodes and TMDs reduces the Fermi level pinning and retains the intrinsic transport behavior of TMDs. The selector with a single type of TMD exhibits a trade‐off between current density and nonlinearity depending on the barrier height. By tuning the Schottky barrier height and controlling the thickness of p‐type WSe2 in MoS2/WSe2/MoS2 n‐p‐n selector for a punch‐through transport, the selector shows high nonlinearity (≈ 230) and high current density (2 × 103 A cm−2) simultaneously. The n‐p‐n selectors are further integrated with a bipolar hexagonal boron nitride memory and calculate the maximum crossbar size of the 2D material‐based one‐selector one‐resistor according to a 10% read margin, which offers the possible realization of future 3D monolithic integration. [ABSTRACT FROM AUTHOR]

Van der Waals (vdW) heterojunctions, with their unique electronic and optoelectronic properties, have become promising candidates for photodetector applications. Amplifying the contribution of the depletion region in vdW heterojunction, which would enhance both of the collection efficiency and speed of the photogenerated carriers, presents an effective strategy for achieving high performance vdW heterojunction photodetectors. Herein, a fully depleted vdW heterojunction photodetector is built on two-dimensional (2D) semiconductor materials (GaTe and InSe) layered on a pattered bottom electrode in vertical structure, in which the generation and motion of carriers are exclusively achieved in the depletion region. Attributed to the intrinsic built-in electric field, the elimination of series resistance and the depletion region confinement of carriers, the as-fabricated photodetector exhibits prominent photovoltaic properties with a high open-circuit voltage of 0.465 V, as well as photoresponse characteristics with outstanding responsivity, detectivity and photoresponse speed of 63.7 A/W, 3.88 × 1013 Jones, and 32.7 μs respectively. The overall performance of this fully depleted GaTe/InSe vdW heterojunctions photodetectors are ranking high among the top level of 2D materials based photodetectors. It indicates the device architecture can provide new opportunities for the fabrication of high-performance photodetectors.

Photodetectors with high responsivity, fast response, and broad spectral response are of great importance for a wide range of applications in fundamental science and various industries. However, conventional photodiodes operating at low bias voltage do not provide any gain. The graphene (Gr)/Si van der Waals heterostructure, on the other hand, offers a potential gain due to the limited density of states near the Dirac point. In this work, a highly photoresponsive broadband pyramidal black‐Si/Gr heterojunction photodetector is presented. The device, with an active area of 5×5 mm2 and a bias voltage of −5 V, exhibits an ultra‐high responsivity of 4.1 A W−1. The photoresponsivity can be further increased to 1379 A W−1 by reducing the device area. Comparative experiments reveal that the pyramidal black‐Si/Gr photodetectors exhibit the largest responsivity compared with pyramidal‐Si/Gr and flat‐Si/Gr photodetectors. The gain in pyramidal black‐Si/Gr photodetectors is attributed to both the pyramidal nanoporous structures and the shift of the Fermi level of Gr under bias. Furthermore, the high responsivity and stable operation of the photodetectors enable the demonstration of imaging applications. The results provide a new strategy for enhancing the performance of photodetectors based on 2D materials. [ABSTRACT FROM AUTHOR]

In this work, a high‐performance two‐terminal n‐MoSe2/p‐GeSn/n‐Ge van der Waals (vdW) heterojunction phototransistor (HPT) is proposed and demonstrated for short‐wave infrared (SWIR) detection. With a high Sn content of 17.1% in the GeSn base region, the cutoff wavelength is extended to beyond 2400 nm. The substantial electron/hole injection ratio resulting from the large bandgap offset between the MoSe2 emitter and the GeSn base enables the harvesting of high photocurrent gain. A record high responsivity of 12.75 A W−1 and an excellent specific detectivity of 1.74 × 1010 Jones at 2250 nm are achieved under a collector‐emitter bias of 1.0 V at room temperature. A response time of 462 µs at 1550 nm outbalancing that of most vdW junction‐based devices is obtained for the non‐optimized devices. Those results show that the mixed‐dimensional GeSn HPT is one of the promising candidates for detection of infrared band above 2 µm. [ABSTRACT FROM AUTHOR]

The heterojunction integration of two-dimensional (2D) materials via van der Waals (vdW) forces, unencumbered by lattice and processing constraints, constitutes an efficacious approach to enhance the overall optoelectronic performance of photodetectors, due to an assortment of distinctive light-matter interactions. Nonetheless, vdW heterojunction photodetectors based on transition metal dichalcogenides (TMDs) face an inevitable trade-off between low dark currents and high responsivity, curtailing the application potential of myriad novel optoelectronic components in sensing, spectral, and communication systems. In this study, we present the successful actualization of a highly sensitive, self-powered, and gate-tunable bipolar response photodetector. The mechanisms underlying photocurrent generation were scrutinized via bias-, power-, and position-dependent mapping photoresponse measurements, identifying the photovoltaic effect, which is attributable to the Schottky junction's built-in electric field, as the predominant mechanism. The prototype Au-WS2-graphene photodetector exhibits a remarkable light on/off ratio of 1.2 × 106, a specific detectivity of 6.12 × 1011 cm Hz1/2 W−1 with 20 μs response time at 638 nm. The wide gate-tunable responsivity provides an adjustability scope, ranging from 0.9 to 3.1 A W−1. Notably, the device demonstrates an exceptional linear photocurrent response, with a linear dynamic range (LDR) value approximating 130 dB, which significantly surpasses that of other photodetectors based on TMDs. [ABSTRACT FROM AUTHOR]

We report a computational study on the possibility of designing nanoscale organic tunnel field-effect transistors (OTFETs) with a subthreshold swing (SS) much smaller than 60 mV/dec and on-state current (Ion) much larger than that of conventional organic field-effect transistors. The OTFETs are designed on the basis of two-dimensional metallophthalocyanine covalent-organic frameworks (2D MPc-COFs) by employing first-principles and quantum-transport approaches in the ballistic-transport regime. The designed OTFETs with architecture of the van der Waals heterojunction manifest themselves with SS as small as 21 mV/dec and Ion as large as 887.5 μA/μm. These devices outperform most tunnel field-effect transistors reported in the literature and fulfill the IRDS (International Roadmap for Devices and Systems) requirement for both high-performance (HP) and low-power (LP) devices. We reveal that 2D MPc-COFs with moderate band gaps are highly required to optimize the device performance. This study provides an insight into the promising application of 2D COFs beyond conventional organic materials in the rational design of HP and LP nanoscale OTFETs. [ABSTRACT FROM AUTHOR]

Self-powered photodetectors that do not require external power support are expected to play a key role in future photodetectors due to their low power characteristics, but achieving high responsivity remains a challenge. 2D van der Waals heterojunctions are a promising technology for high-performance self-powered photodetectors due to their excellent optical and electrical properties. Here, we fabricate a self-powered photodetector based on In2Se3/WSe2/ReS2 van der Waals heterojunction self-powered photodetector. Due to the presence of ReS2 layer, photocurrent is enhanced as a result of the increase in light absorption efficiency and the effective region for generating photogenerated carriers. The built-in electric field is enhanced by a negative 'back-gate voltage' along the p–n junction vertical direction generated by the electrons in the photo-generated electrons accumulation layer. Accordingly, the optical responsivity and the photoresponse speed of this heterojunction self-powered photodetector are greatly boosted. The proposed self-powered photodetector based on the In2Se3/WSe2/ReS2 heterojunction exhibits a high responsivity of 438 mA W−1, which is 17 times higher compared to the In2Se3/WSe2 photodetector, a self-powered current (1.1 nA) that is an order of magnitude higher than that of the In2Se3/WSe2 photodetector, and a fast response time that is 250% faster. Thus the self-powered photodetector with a stronger built-in electric field and a wider depletion zone can provide a new technological support for the fabrication of high responsivity, low power consumption and high speed self-powered photodetectors based on van der Waals heterojunctions. [ABSTRACT FROM AUTHOR]

In recent years, 2D reconfigurable phototransistors (RPTs) have been applied in broadband convolutional processing, retinomorphic hardware devices, and non‐volatile memorizers. However, there has been a lack of investigation into all‐2D Schottky junctions used in RPT with polarity control behavior. Herein, a vertically stacked multilayered WS2/WTe2 Schottky RPT is reported. The semimetal characteristics of 1T'‐WTe2 is designed to form a built‐in electric field of 69 meV across the heterojunction and WS2 exhibits gate‐tunable characteristics. Therefore, reconfigurable rectifying behavior and self‐driven bidirectional photo response can be achieved. The phototransistor possesses a gate‐tunable rectification ratio ranging from 10−2 to 105, and the corresponding logic half‐wave rectifier shows excellent switchable rectifying states. Under 635 nm illumination, the responsivity can be adjusted from −1325 to 430 mA W−1 with reversed signs. Meanwhile, the maximum power conversion efficiency is 2.84%, and the specific detectivity is 1.47 × 1012 Jones. The device shows both negative and positive responsivity with linear gate dependence within a voltage window of 10 V. Impressively, nonvolatile photovoltaic performance can be demonstrated by reversing short‐circuit current and open‐circuit voltage by applying and releasing pulsed gate voltage. Finally, reconfigurable polarization behavior, single‐pixel imaging, and the optical logic circuit are applicable to the heterostructure. [ABSTRACT FROM AUTHOR]

Two-dimensional transition metal dichalcogenides (2DTMDs) and their van der Waals heterojunctions (vdWHs) have garnered significant attention working as the channel material of optoelectronics. The development of new heterojunction growth schemes may also provide better performance for optoelectronic devices. In this paper, PtSe2 thin films with controllable size and thickness are directly grown on MoS2 nanosheet by sputtering-selenization two-step growth method. The photodetector with PtSe2/MoS2 heterojunction exhibits a type-I band alignment and leads to an impressive broadband spectral photoresponse (405 to 1550 nm). It can achieve responsivity as high as 5.42 A/W, a detectivity of 2.52 × 1010 Jones, and a fast response rate (92/112 μs for rise/fall time respectively). In addition, the device has excellent stability in the air atmosphere and keeps its photoresponse after even six months. The in-situ growth method provides a new scheme to construct heterojunctions of 2DTMDs and develop energy-efficient photodetectors with enhanced performance. It also supplements the practical production and application of large-scale broadband detectors.

Abstract In recent years, 2D reconfigurable phototransistors (RPTs) have been applied in broadband convolutional processing, retinomorphic hardware devices, and non‐volatile memorizers. However, there has been a lack of investigation into all‐2D Schottky junctions used in RPT with polarity control behavior. Herein, a vertically stacked multilayered WS2/WTe2 Schottky RPT is reported. The semimetal characteristics of 1T’‐WTe2 is designed to form a built‐in electric field of 69 meV across the heterojunction and WS2 exhibits gate‐tunable characteristics. Therefore, reconfigurable rectifying behavior and self‐driven bidirectional photo response can be achieved. The phototransistor possesses a gate‐tunable rectification ratio ranging from 10−2 to 105, and the corresponding logic half‐wave rectifier shows excellent switchable rectifying states. Under 635 nm illumination, the responsivity can be adjusted from −1325 to 430 mA W−1 with reversed signs. Meanwhile, the maximum power conversion efficiency is 2.84%, and the specific detectivity is 1.47 × 1012 Jones. The device shows both negative and positive responsivity with linear gate dependence within a voltage window of 10 V. Impressively, nonvolatile photovoltaic performance can be demonstrated by reversing short‐circuit current and open‐circuit voltage by applying and releasing pulsed gate voltage. Finally, reconfigurable polarization behavior, single‐pixel imaging, and the optical logic circuit are applicable to the heterostructure.

High‐performance and versatile multifunctional photodetection devices are essential for various applications, but they often face severe challenges, such as limited operating modes and low detection sensitivity. In this study, a multifunctional detector based on InSe/VO2 heterojunction that integrates light and electric field perceiving capabilities and can dynamically switch operating modes is presented. The device can serve as a self‐powered photodetector, logic gates, and an artificial nociceptor, showcasing its versatility and potential for various applications. The unique metal‐insulator transition (MIT) of VO2 enables the device to dynamically switch between self‐powered photovoltaic and photoconductive modes. A significant advance over traditional photodetectors that can only operate in a single mode has been realized. The device exhibits high detectivity up to 2.09 × 1013 Jones and excellent responsivity of 6.15 A W−1, making it a reliable and accurate tool for photodetection. In addition, it functions as "AND" and "OR" logic gates, providing opportunities for signal processing and communication. Moreover, by adding electric pulses to the InSe/VO2 heterojunction, the device can also function as an artificial nociceptor, with potential implications for medical applications and prosthetics. This work presents remarkable progress toward intelligent sensors and systems, with transformative potential for electronic and photonic devices. [ABSTRACT FROM AUTHOR]

The electronic structure and optical properties of van der Waals heterostructures with different layers of MoS2 and VS2 stacks were studied by first-principles calculations based on density functional theory. The stability of two heterojunctions at room temperature was verified through ab initio molecular dynamics. In addition, both heterojunctions exhibit p-type Schottky contact. But compared to the heterojunction composed of monolayer MoS2, the barrier height in the heterojunction formed by the stacking of bilayer MoS2 and VS2 significantly decreases from 0. 36 eV to 0. 08 eV, effectively forming a low contact resistance and reducing the energy loss of carrier transport. The calculation of the light absorption spectrum indicates that the heterojunction composed of bilayer MoS2 has higher absorption peaks. The research results provide a theoretical basis for the design of heterojunctions based on MoS2 and their applications in high-performance optoelectronic devices. [ABSTRACT FROM AUTHOR]

Van der Waals heterostructures of black phosphorous(BP) and Molybdenum Disulfide(MoS2) is designed and evaluated for photodetection application from visible to mid-infrared wavelength up to 4.5 μm. The device possesses a low dark current less than 0.1 μA for short wavelength light. For visible and near infrared radiation, the contribution of heat and photo energy to current enhancement is analyzed. Dark current drift by joule heat and laser heat absorbed is observed in short waveband. The difference in response speed is believed to be a result of the competition of BP and MoS2 photocurrent. Gate tunable response time and on-off ratio makes the device versatile in potential application. For mid infrared radiation, BP-MoS2 heterojunction with a dedicated thickness tailoring of MoS2 exhibits similar negative response as an intrinsic BP. The normalized detectivity is ${D}^*$ of $2.02 \times {10}^8\ Jones$ for the 4.5 μm mid-infrared radiation. Elaborate reduction of the noise is conducted to get the time resolvable photo-response. A low bias is necessary for a time resolved photocurrent, reducing the flicker noise to an acceptable level.

Recently, van der Waals heterojunctions (vdWHs) constructed from two two-dimensional materials have attracted considerable attention. In particular, vdWHs based on black phosphorus (BP) have shown excellent photoelectric properties. In this work, we construct a BP/GeTe vdWH and investigate its electronic and optical properties. We find that the BP/GeTe vdWH has a type-II band alignment. Its optical absorption exhibits a red shift compared to the freestanding BP and GeTe monolayers. The electric field and strain effects on the BP/GeTe vdWH are also investigated. The band offsets can be modulated by the electric field and the strain. The BP/GeTe vdWH will convert from type-II to type-I when applying an electric field and to type-III under strain, which will expand the application of BP/GeTe vdWHs in transistor devices. Furthermore, the strain can significantly enhance the optical absorption and induce the red shift of the absorption edge, which indicates the broad applications of the BP/GeTe vdWH in photodetector devices. [ABSTRACT FROM AUTHOR]

Utilization of semiconductor photocatalyst materials to degrade pollutants for addressing environmental pollution problems has become a research focus in recent years. In this work, a 2D/2D S-scheme crystalline carbon nitride (CCN)/BiOIO3 (BOI) van der Waals heterojunction was successfully constructed for effectively enhancing the degradation efficiency of antibiotic contaminant. The as-synthesized optimal CCN/BOI-3 sample exhibited the highest efficiency of 80% for the photo-degradation of tetracycline (TC, 20 mg/L) after 120 min visible light irradiation, which was significantly higher than that of pure CCN and BOI. The significant improvement in photocatalytic performance is mainly attributed to two aspects: (i) the 2D/2D van der Waals heterojunction can accelerate interface carriers' separation and transfer and afford sufficient active sites; (ii) the S-scheme heterojunction elevated the redox capacity of CCN/BOI, thus providing a driving force for the degradation reaction. The degradation pathways of TC for the CCN/BOI composite were investigated in detail by liquid chromatography-mass spectrometry (LC-MS) analysis. This work provides a design idea for the development of efficient photocatalysts based on the 2D/2D S-scheme van der Waals heterojunctions. [ABSTRACT FROM AUTHOR]

The 2D/2D van der Waals heterojunctions have promising photocatalytic applications. However, their interfacial interaction and photocatalytic mechanism are still unclear. Herein, monolayer black phosphorus (BP)/graphitic carbon nitride (GCN) heterojunction photocatalytic hydrogen evolution is systematically investigated using the density‐functional theory method. It is indicated in the results that BP/GCN heterojunction structure distortion and interface interaction change its electronic structure and photocatalytic performance. The hydrogen‐adsorption free energy of BP/GCN heterojunction is −0.28 eV, indicating that the BP/GCN heterojunction has a high catalytic activity for hydrogen production. Calculated Bader charge and Fermi energy level show that a built‐in electric field from BP to GCN forms in its interface. The energy barrier and built‐in electric field promote the recombination of photogenerated electrons in GCN conduction band and photogenerated holes in BP valence band; electrons on the BP conduction band and holes on the GCN valence band are effectively separated in space; and more electrons and holes can participate in redox reactions on the surface. The BP/GCN heterojunction is a type Z heterojunction. Significant improvement in photocatalytic reaction efficiency is attributed to the type Z photocatalytic mechanism and small free energy of hydrogen adsorption. Herein, it is aimed to offer insights into the photocatalytic mechanism of 2D/2D heterojunctions. [ABSTRACT FROM AUTHOR]

Transparent photodetectors with the optical signal recognition and conversion capabilities are the core component for smart sensors and next‐generation "see‐through" optoelectronics. However, it is usually difficult to have both excellent optical transmittance and photoresponse performance, which hinders the practicality of transparent photodetectors. Herein, a photogating effect enhanced transparent ultraviolet (UV) photodetector is demonstrated based on the TiO2/MXene van der Waals heterojunction. By simply spin‐coating MXene nanosheets on TiO2 film, the UV photodetector exhibits significantly enhanced performance, such as ultrahigh responsivity (202.4 A/W), large specific detectivity (1.79 × 1014 Jones) and outstanding external quantum efficiency (1.02 × 105%), which are three orders of magnitude higher than those of pure TiO2 film. Meanwhile, the device exhibits up to 95% transparency in the visible range. Both the experimental results and theory calculations indicate that local Schottky junctions are established at the TiO2/MXene interface. These local junctions exert a giant photogating effect under illumination, which can facilitate the separation of photogenerated carriers and improve the photodetection performance. Moreover, the transparent photodetector has been successfully applied in a UV index wireless sensing system. This work demonstrates the ingenious application of MXene in optoelectronics and provides insight into the design of high‐performance transparent photodetectors. [ABSTRACT FROM AUTHOR]

The Janus structure has a built-in electric field due to the different atoms on its two sides. In the present work, hexagonal PdSSe with Janus structure is compounded with graphene to form a van der Waals heterostructure. The geometric and electronic structures are investigated by first-principles calculations based on density functional theory. Two types of stacking, Se side and S side in contact with graphene, are considered in the calculations. When the S-side is in contact with graphene, the system has smaller equilibrium spacing and larger charge transfer with lower binding energy. N-type Ohmic contacts are formed when the S-side is in contact with graphene, n-type Schottky contacts with extremely low potential barriers are formed when the Se-side is in contact with graphene. Finally, the effect of vertical strain on the contact properties is discussed. The contact type of PdSSe/graphene is significantly tunable by applying vertical strain. [ABSTRACT FROM AUTHOR]

[Display omitted] • Semiconductor-metal ZrX 2 (X = Cl, Br, I) /Zr 2 Cl 2 heterojunctions is constructed and studied. • ZrI 2 /Zr 2 Cl 2 exhibits a very low p-type Schottky barrier height. • ZrI 2 /Zr 2 Cl 2 achieves Ohmic contact by a relatively low positive electric field. • All heterojunctions hold a high intrinsic light absorption capability. Exploring metal–semiconductor electrical contact behaviors is highly desirable for developing high-performance new devices. Here, transition metal halide ZrX 2 (X = Cl, Br, I)/Zr 2 Cl 2 vdW heterojunctions are constructed by semiconducting ZrX 2 and metallic Zr 2 Cl 2 monolayers. Our calculations reveal that such metal–semiconductor heterojunctions possess very high energetic, thermal, dynamic and mechanical stability, with p-type Schottky contacts in the intrinsic state, and their Schottky barrier height (SBH) decreases with the atom number of haloid elements increased. Particularly, ZrI 2 /Zr 2 Cl 2 heterojunction exhibits a very low p-type SBH, 0.18 eV, favorably to design high-performance Schottky devices. Their electronic and electrical contact properties can also be modulated by physical field coupling effects. For example, p-type SBH decreases continuously to obtain quasi-Ohmic contact under applied compressive strain, and the p-type Schottky contact can be transformed to p-type Ohmic contacts under suitable positive external electric field for all heterojunctions. Particularly, ZrI 2 /Zr 2 Cl 2 heterojunction achieves Ohmic contact by a relatively low positive electric field, 0.15 V/Å. It is also shown that all heterojunctions possess high intrinsic light absorption capability. The light absorption performance of ZrBr 2 /Zr 2 Cl 2 heterojunction would undergo a significant enhancement under electric field. Therefore, these suggested heterojunctions hold promising application potentials for developing electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract Ferroelectric two dimensional (2D) materials hold great potential to develop modern miniaturized electronic and memory devices. 2D ferroelectrics exhibiting spontaneous polarization in the out‐of‐plane direction have been extensively investigated to date, but the loss of their polarization during device operation has been problematic. Although 2D materials with in‐plane ferroelectric behavior are more stable against depolarization and thus promising for memory and logic applications, experimental realization of in‐plane 2D ferroelectric devices is still scarce. Here, we demonstrate in‐plane ferroelectric field effect transistors (FETs) based on a van der Waals heterojunction (vdWHJ), which can perform multibit memory and logic operations. Tin monosulfide (SnS), a 2D material with in‐plane ferroelectricity, is partially stacked on top of a semiconducting molybdenum disulfide (MoS2) on a silicon dioxide (SiO2)‐coated silicon substrate to fabricate vdWHJ FETs in back‐gate configuration. Switching of the in‐plane polarization direction in the SnS channel modulates the contact barriers at the electrode/SnS and SnS/MoS2 interfaces, thereby creating high resistance states and low resistance states (LRS). The device exhibits a logic transfer characteristic with a high drain current on/off ratio (>106) in LRS and non‐volatile memory performance with excellent retention characteristics (extrapolated retention time > 10 years). With exquisite tuning of the channel resistance by SnS polarization and gate bias, we realize multiple states with distinct current levels for multibit memory and logic operations suitable for programmable logic‐in‐memory applications.

Van der Waals (vdW) heterojunction has emerged as promising building blocks for the next generation of optoelectronics, which can fulfill the increasing demands of miniaturization, high density of integration, and low power consumption. The photovoltaic effect is one of the crucial functions for fast photo‐detection and energy‐harvesting applications. Here, graphene is integrated into vdW WS2/WSe2 heterojunction, the graphene can serve as electron and hole transport layers, boosting the collection efficiency of photo‐excited carriers and thus improving the photovoltaic effect. The graphene‐integrated device exhibits superior power‐conversion‐efficiency (PCE) up to 9.08%, one order of magnitude improvement compared to the device with metal‐WS2/WSe2‐metal configuration. Moreover, the back gate has great modulation on its photovoltaic effect due to the large gate‐tunability of band bending at the interface. Operating as self‐driven photo‐diode, it also achieves outstanding photodetection performance with high photo‐switching ratio of 1 × 106, high detectivity (D*) of 2.66 × 1012 Jones, and fast speed of 110 µs, all the parameters are improved by nearly one order of magnitude compared to the device without graphene integration. This work provides a universal approach by integrating graphene as vdW contact to significantly improve the photovoltaic effect and photodetection property toward highly efficient energy‐harvest and photodetector applications. [ABSTRACT FROM AUTHOR]

Synergy between superconductivity and ferromagnetism may offer great opportunities in nondissipative spintronics and topological quantum computing. Yet at the microscopic level, the exchange splitting of the electronic states responsible for ferromagnetism is inherently incompatible with the spin-singlet nature of conventional superconducting Cooper pairs. Here, we exploit the recently discovered van der Waals ferromagnets as enabling platforms with marvelous controllability to unravel the myth between ferromagnetism and superconductivity. We report unambiguous experimental evidence of superconductivity in few-layer ferromagnetic Fe 3 GeTe 2 (FGT) proximity coupled to a superconducting NbSe 2 overlayer through an insulating spacer, demonstrating coexistence of these two seemingly antagonistic orderings. Our transport measurements reveal a sudden resistance drop to zero in FGT below the superconducting critical temperature of NbSe 2 and detect a Josephson supercurrent through the NbSe 2 /insulator/FGT van der Waals junction. Furthermore, using anomalous Hall effect and magnetic force microscopy characterizations, we confirm that FGT preserves its ferromagnetism in the superconducting regime. Our central findings reveal the microscopic harmony between ferromagnetism and superconductivity and render these systems immense technological potentials.

The contact type between graphene and semiconducting two-dimensional materials is a crucial factor in determining the performance of nanoscale electronic devices based on two-dimensional materials. Recently, SiCP4 is proposed to have high charge mobility plus high stability. In this work, we study the contact type between graphene and SiCP4. The Schottky barrier is formed between graphene and SiCP4. By changing the interlayer distance, the Schottky barrier can be tuned in a wide range. The charge transfer at the interface induces a reverse shift between the bands of graphene and SiCP4. The amount of charge transfer can be used to explain the change in the Schottky barrier. Furthermore, the Schottky barrier can be controlled by applying a vertical electric field. The tunable Schottky barrier provides a guide for the design of the nanodevice based on graphene and SiCP4.

Two-dimensional (2D) Janus transition metal dichalcogenides (JTMDs) exhibit suitable band gaps and strong visible light absorption, which are extensively applied to the field of optoelectronic devices. Here, we investigate the electronic properties of 2D JTMDs MSeS (M = Hf, Zr) and SnS2 van der Waals heterojunction through density functional theory. The calculated electronic properties reveal that ZrSeS/SnS2 heterojunction has a type-I band alignment, while HfSeS/SnS2 heterojunction has a type-II band alignment. We build the diodes based on the MSeS (M = Hf, Zr)/SnS2 heterojunctions and study the electronic transport. The currents of the devices exhibit asymmetry, and the negative turn-on voltages suggest that constructed devices are backward diodes. Moreover, it is found that the gate voltage can modulate the rectifying ratio, and the rectifying performance of ZrSeS/SnS2 is better than that of HfSeS/SnS2.. [ABSTRACT FROM AUTHOR]

• Ultra-high vacuum environment enables ultra-clean MoS 2 /Au(111) interfaces. • Millimeter-sized monolayer and sub-millimeter-sized bilayer MoS 2 form on Au(111). • The bilayer MoS 2 on Au(111) exhibits a tunable semiconducting band gap. • A 0.54 eV Schottky barrier forms at the MoS 2 /Au(111) contact. Fabricating heterojunctions with precisely controlled interfacial structures is crucial for exploring novel low-dimensional physics and for realizing high-performance devices. However, such capabilities are often constrained by contamination from the ambient environment or by the limitations of applicable methods and materials under vacuum conditions. In this study, MoS 2 /Au(111) heterostructures were fabricated by exfoliating MoS 2 thin layers onto a crystallized Au(111) surface using a gold-assisted exfoliation method in an ultra-high vacuum environment. This method yields millimeter-sized monolayer or sub-millimeter-sized bilayers with contamination-free interfaces, which are unattainable for samples made in air. Scanning tunneling microscopy revealed that both the monolayer and the bilayer exhibit uniform and well-ordered moiré superlattices controlled by the twisting angle between the Au(111) surface and the MoS 2 overlayer. The direct contact with the Au surface renders the monolayer MoS 2 weakly metallic, while a less coupled bilayer is semiconducting, indicating a 0.54 eV Schottky barrier for the MoS 2 /Au(111) contact. This method is applicable to various combinations of van der Waals materials and metal surfaces. The uniform and controllable heterojunctions can serve as ideal model systems for exploring semiconductor–metal interfaces and atomic structures formed within. [ABSTRACT FROM AUTHOR]

Employing liquid metal peeling techniques, we developed a Bi x Sn 1-x O 2 /Ga 2 O 3 heterojunction ultraviolet (UV) photodetector. This device delivers high sensitivity and excellent photoelectric performance, with a notable responsivity of 3.16 A/W and a detectivity (D∗) reaching 4.48 × 1012 Jones under 255 nm UV illumination at a light intensity of 341 μW/cm2, biased at 5V. It also features rapid response times, with a rising time of 58 ms, along with a decaying time of 190 ms. Notably, the liquid metal peeling method for creating oxide heterojunction opens up significant potential for the advancement of high-performance UV photodetectors based on 2D van der Waals heterojunction. • Fabricated BTO/Ga2O3 p-n junction via liquid metal process for UV photodetector with high responsivity (3.16 A/W) and detectivity (4.48×1012 Jones). • Shows potential for efficient weak light detection and optical signal conversion in heterojunction, a candidate for next-gen optoelectronic devices. • Strategy for fabricating oxide-based van der Waals heterojunctions for UV optoelectronics. [ABSTRACT FROM AUTHOR]

We construct GeC/SiC x (x = 1,2,7) van der Waals heterojunctions to study the photoelectric properties. The first-principle calculations show that three heterojunctions have the Z-type band alignment by analyzing the charge transfer paths. The designed heterojunctions possess good optical absorption in the visible light region, suggesting potential applications in photocatalysis, solar cells, and other photovoltaic devices. It is found that GeC/SiC and GeC/SiC 7 heterojunctions fulfill the requirements as photocatalysts from PH = 0 to PH = 14. Although the GeC/SiC 2 heterojunction fulfills the requirements as a photocatalyst from PH = 6 to PH = 10, the GeC/SiC 2 -based solar cell presents excellent performance, whose power conversion efficiency reaches 24.6 % theoretically. The results demonstrate that GeC/SiC x (x = 1, 2, 7) is a potential candidate for photocatalytic and solar cell materials in the future. [Display omitted] [ABSTRACT FROM AUTHOR]