Vertical Van Der Waals Heterostructures Research Articles

Vertical MoSe2–WSe2 p-n Heterojunctions Grown by One-Pot Chemical Vapor Deposition for Ultrafast Photodetection

Two-dimensional transition metal dichalcogenides (TMDCs) have been extensively studied in the last decade due to their atomic thin structure and unique optoelectronic properties. In particular, lateral and vertical van der Waals heterostructures by combining different transition metal dichalcogenides (TMDCs) have been studied to develop the potential applications of two-dimensional materials. However, the optical properties are challenging due to the limited quality of TMDCs based heterojunctions. In this work, vertical MoSe2/WSe2 p–n heterojunctions have been synthesized by one-pot chemical vapor deposition (CVD) method. The MoSe2 -WSe2 heterostructure exhibits rectification characteristics of a p-n junction with the rectification ratio of 100 at ±10V bias. The phototransistor based on MoSe2/WSe2 p-n heterojunction shows a photoresponse of visible(638nm). The responsivity can reach up to 20 A/W, and the detectivity is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.5\times 10^{13}$ </tex-math></inline-formula> Jones. Most importantly, the optical response time of the MoSe2/WSe2 p-n heterojunction is as fast as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$28 ~\mu $ </tex-math></inline-formula> s. The results indicate that vertical MoSe2/WSe2 p-n heterojunction could be a prospective candidate for high-performance optoelectronic devices.

Sequential Growth of Vertical Transition-Metal Dichalcogenide Heterostructures on Rollable Aluminum Foil.

Vertical van der Waals heterostructures (vdWhs), which are made by layer-by-layer stacking of two-dimensional (2D) materials, offer great opportunities for the development of extraordinary physics and devices such as topological superconductivity, robust quantum Hall phenomenon, electron-hole pair condensation, Coulomb drag, and tunneling devices. However, the size of vdWhs is still limited to the order of a few micrometers, which restricts the large-scale roll-to-roll processes for industrial applications. Herein, we report the sequential growth of a 14 in. vertical vdWhs on a rollable Al foil via chemical vapor deposition. By supplying chalcogen precursors to liquid transition-metal precursor-coated Al foils, we grew a wide range of individual 2D transition-metal dichalcogenide (TMD) films, including MoS2, VS2, ReS2, WS2, SnS2, WSe2, and vanadium-doped MoS2. Additionally, by repeating the growth process, we successfully achieved the layer-by-layer growth of ReS2/MoS2 and SnS2/ReS2/MoS2 vdWhs. The chemically inert Al native oxide layer inhibits the diffusion of chalcogen and metal atoms into Al foils, allowing for the growth of diverse TMDs and their vdWhs. The conductive Al substrate enables the effective use of vdWhs/Al as a hydrogen evolution reaction electrocatalyst with a transfer-free process. This work provides a robust route for the commercialization of 2D TMDs and their vdWhs at a low cost.

Electrically Controlled Wavelength-Tunable Photoluminescence from van der Waals Heterostructures.

Achieving facile control of the wavelength of light emitters is of great significance for many key applications in optoelectronics and photonics, including on-chip interconnection, super-resolution imaging, and optical communication. The Joule heating effect caused by electric current is widely applied in modulating the refractive index of silicon-based waveguides for reconfigurable nanophotonic circuits. Here, by utilizing localized Joule heating in the biased graphene device, we demonstrate electrically controlled wavelength-tunable photoluminescence (PL) from vertical van der Waals heterostructures combined by graphene and two-dimensional transition metal dichalcogenides (2D-TMDCs). By applying a moderate electric field of 6.5 kV·cm-1 to the graphene substrate, the PL wavelength of 2D-TMDCs exhibits a continuous tuning from 662 to 690 nm, corresponding to a bandgap reduction of 76 meV. The electric control is highly reversible during sweeping the bias back and forth. The temperature dependence of Raman and PL spectroscopy reveals that the current-induced local Joule heating effect plays a leading role in reducing the optical direct bandgap of TMDCs. The bias-dependent optical reflectivity and time-resolved photoluminescence measurements show a consistent reduction of the optical band gap of 2D-TMDCs and increased PL lifetimes with the electric field over the heterostructures. Moreover, we demonstrate the consistent device operation from 2D materials grown by chemical vapor deposition, showing great advantages for the scalability.

Atomically Sharp Lateral Superlattice Heterojunctions Built‐In Nitrogen‐Doped Nanoporous Graphene

Nanometer scale lateral heterostructures with atomically sharp band discontinuities can be conceived as the 2D analogues of vertical Van der Waals heterostructures, where pristine properties of each component coexist with interfacial phenomena that result in a variety of exotic quantum phenomena. However, despite considerable advances in the fabrication of lateral heterostructures, controlling their covalent interfaces and band discontinuities with atomic precision, scaling down components and producing periodic, lattice-coherent superlattices still represent major challenges. Here, a synthetic strategy to fabricate nanometer scale, coherent lateral superlattice heterojunctions with atomically sharp band discontinuity is reported. By merging interdigitated arrays of different types of graphene nanoribbons by means of a novel on-surface reaction, superlattices of 1D, and chemically heterogeneous nanoporous junctions are obtained. The latter host subnanometer quantum dipoles and tunneling in-gap states, altogether expected to promote interfacial phenomena such as interribbon excitons or selective photocatalysis.

Overall High-Performance Near-Infrared Photodetector Based on CVD-Grown MoTe2 and Graphene Vertical vdWs Heterostructure

Two-dimensional (2D) materials, such as graphene and transition metal dichalcogenides (TMDCs), are highly appealing in the fields of electronics, optoelectronics, energy, etc. Graphene, with high conductivity and high carrier mobility, is an excellent candidate for transparent electrodes. TMDCs have remarkably strong light absorption in the range of visible to infrared wavelength. High-performance photodetectors are expected to achieve through the combination of graphene and TMDCs. Nowadays, near-infrared (NIR) photodetectors play significant roles in many areas. MoTe2 with bandgap energy of about 1.0 eV in its bulk form is a promising material for cost-saving NIR photodetectors. Thus far, only a few of the reported studies on NIR photodetectors built on MoTe2/graphene heterostructures have achieved high responsivity and short response time simultaneously in one device. In this study, we fabricate graphene–MoTe2–graphene vertical van der Waals heterostructure devices through chemical vapor deposition (CVD) growth, wet transfer method, and dry etching technique. Under 1064 nm laser illumination, we acquire responsivity of as high as 635 A/W and a response time of as short as 19 μs from the as-fabricated device. Moreover, we acquire higher responsivity of 1752 A/W and a shorter response time of 16 μs from the Al2O3-encapsulated device. Our research drives the application of 2D materials in the NIR wavelength range.

Controllable Preparation of 2D Vertical van der Waals Heterostructures and Superlattices for Functional Applications

2D van der Waals heterostructures (vdWHs) and superlattices (SLs) with exotic physical properties and applications for new devices have attracted immense interest. Compared to conventionally bonded heterostructures, the dangling-bond-free surface of 2D layered materials allows for the feasible integration of various materials to produce vdWHs without the requirements of lattice matching and processing compatibility. The quality of interfaces in artificially stacked vdWHs/vdWSLs and scalability of production remain among the major challenges in the field of 2D materials. Fortunately, bottom-up methods exhibit relatively high controllability and flexibility. The growth parameters, such as the temperature, precursors, substrate, and carrier gas, can be carefully and comprehensively controlled to produce high-quality interfaces and wafer-scale products of vdWHs/vdWSLs. This review focuses on three types of bottom-up methods for the assembly of vdWHs and vdWSLs with atomically clean and electronically sharp interfaces: chemical/physical vapor deposition, metal-organic chemical vapor deposition, and ultrahigh vacuum growth. These methods can intuitively illustrate the great flexibility and controllability of bottom-up methods for the preparation of vdWHs/vdWSLs. The latest progress in vdWHs and vdWSLs, related physical phenomena, and (opto)electronic devices are summarized. Finally, the authors discuss current challenges and future perspectives in the synthesis and application of vdWHs and vdWSLs.

Water assisted growth of two-dimensional MoS2/MoSe2 vertical heterostructures on molten glass.

Herein, we demonstrate a chemical vapor deposition route to the controlled growth of large scale MoS2/MoSe2 vertical van der Waals heterostructures on a molten glass substrate using water as the oxidizing chemical to guarantee a sufficient and uniform delivery of the metal precursor. This work offers an efficient way for developing other layered heterostructures for integrated electronic and optoelectronic devices.

Modulation of strain on electronic structure and contact type of BP/SnS van der waals heterostructure

Vertical van der Waals heterostructures (vdWH) composed of two monolayer (ML) materials can provide new opportunities for layered electronic devices. Here we present a detailed theoretical investigation about the electronic properties of BP/SnS vdWH by applying in-plane uniaxial and biaxial strains. Our first principles calculations suggest that the direct bandgap of BP/SnS vdWH can be maintained within a large range of uniaxial and biaxial strains. We also find that the bandgap, band alignment and contact type of BP/SnS vdWH can be tuned by uniaxial and biaxial strains. In addition, the Poisson’s ratio exhibits an intense anisotropy with respect to the uniaxial strain along zigzag (ZZ) and armchair directions. The easily tunable electronic properties and highly anisotropic character of BP/SnS vdWH make it to be a promising material in the field of photovoltaic cells, photodetectors, and other functional nano devices.

Out-of-Plane Transport of 1T-TaS2/Graphene-Based van der Waals Heterostructures.

Due to their anisotropy, layered materials are excellent candidates for studying the interplay between the in-plane and out-of-plane entanglement in strongly correlated systems. A relevant example is provided by 1T-TaS2, which exhibits a multifaceted electronic and magnetic scenario due to the existence of several charge density wave (CDW) configurations. It includes quantum hidden phases, superconductivity and exotic quantum spin liquid (QSL) states, which are highly dependent on the out-of-plane stacking of the CDW. In this system, the interlayer stacking of the CDW is crucial for interpreting the underlying electronic and magnetic phase diagram. Here, atomically thin-layers of 1T-TaS2 are integrated in vertical van der Waals heterostructures based on few-layers graphene contacts and their electrical transport properties are measured. Different activation energies in the conductance and a gap at the Fermi level are clearly observed. Our experimental findings are supported by fully self-consistent DFT+U calculations, which evidence the presence of an energy gap in the few-layer limit, not necessarily coming from the formation of out-of-plane spin-paired bilayers at low temperatures, as previously proposed for the bulk. These results highlight dimensionality as a key effect for understanding quantum materials as 1T-TaS2, enabling the possible experimental realization of low-dimensional QSLs.

γ-GeSe: A New Hexagonal Polymorph from Group IV–VI Monochalcogenides

The family of group IV-VI monochalcogenides has an atomically puckered layered structure, and their atomic bond configuration suggests the possibility for the realization of various polymorphs. Here, we report the synthesis of the first hexagonal polymorph from the family of group IV-VI monochalcogenides, which is conventionally orthorhombic. Recently predicted four-atomic-thick hexagonal GeSe, so-called γ-GeSe, is synthesized and clearly identified by complementary structural characterizations, including elemental analysis, electron diffraction, high-resolution transmission electron microscopy imaging, and polarized Raman spectroscopy. The electrical and optical measurements indicate that synthesized γ-GeSe exhibits high electrical conductivity of 3 × 105 S/m, which is comparable to those of other two-dimensional layered semimetallic crystals. Moreover, γ-GeSe can be directly grown on h-BN substrates, demonstrating a bottom-up approach for constructing vertical van der Waals heterostructures incorporating γ-GeSe. The newly identified crystal symmetry of γ-GeSe warrants further studies on various physical properties of γ-GeSe.

Perspectives on photodetectors based on selenides and their van der Waals heterojunctions

Two-dimensional layered selenides have attracted intense attention in recent years because of their unique structures and physical properties. Many high-performance electrical and optoelectrical devices based on selenides and their heterostructures have been extensively investigated, and photodetectors have been a particular area of attention. Here, we provide a systematic summary of our recent research progress in selenide-based photodetectors. Three different strategies are introduced and discussed, specifically the use bottom metal contacts, graphene contacts, and bandgap engineering-based vertical van der Waals heterostructures. These approaches are effective for improving the performance of photodetectors based on selenides and their heterostructures. Conclusions are given, and several approaches are proposed for further development of selenide-based optoelectrical devices.

Thermodynamic stability of defects in hybrid MoS2/InAs heterostructures

Vertical van der Waals heterostructures created from two chemically different two-dimensional (2D) materials have made significant headway in the current electronic manufacturing landscape since they demonstrate enhanced attributes. Recently, among the wide variety of possible van der Waals heterostructures, a 2D molybdenum disulfide (MoS2) thin film deposited on a 3D indium arsenide (InAs) semiconductor substrate has demonstrated promising properties. To realize the true potential of these hybrid heterostructures, it is imperative to understand their structural stability, as well as the thermodynamic stabilities of various defects at the heterointerface. We report first principles-based electronic structure calculations to study MoS2(100)/InAs(111) heterostructures with two different terminations of the substrate. We present relative stabilities of arsenic-terminated and indium-terminated heterostructures, and shed light on the thermodynamic stabilities of arsenic, indium, and sulfur vacancy defects at the heterointerface. Atomic-scale structure and electronic structure of defects is detailed along with changes in band gaps due to inclusion of vacancy defects. In general, defects are found to be energetically favorable to occur at the interface as compared to the bulk. We offer new insights into the fundamental role of interfaces in hybrid van der Waals heterostructures and their influence on defects, with potential implications for future design of next-generation semiconductors.

Enhanced Photodetection Performance in Graphene-Assisted Tunneling Photodetector

The vertical van der Waals heterostructures based on 2-D materials have attracted tremendous attention in optoelectronic devices as they can offer perfect interface without dangling bonds, atomic layer thicknesses, and conveniently tunable energy band alignment. However, the carrier transport mechanism in vertically stacked van der Waals heterostructure photodetectors is usually neglected in regards of photoresponse enhancement strategy, leading to low photoresponsivity and quantum efficiency. Here, we report a vertically stacked tunneling photodetector based on WSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /graphene/WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> van der Waals heterostructure. By introducing graphene film into the WSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface, the interface composition was ameliorated and the Fowler–Nordheim tunneling (FNT) was enhanced with the reduced tunneling barrier height and thickness, caused by the elevated energy level of electrons since strong electron–electron interaction, ultrafast thermalization (~50 fs), and massless Dirac electrons of graphene. Therefore, the device exhibits a high photocurrent/dark current ratio (>10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> ), fast response time ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 300~ \mu \text{s}$ </tex-math></inline-formula> ), high detectivity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1.58\times 10^{12}$ </tex-math></inline-formula> Jones), and high responsivity (429 mA W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) across a broad spectral range till <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1~ \mu \text{m}$ </tex-math></inline-formula> at room temperature. The optimized detectivity and responsivity are about 150 times and 50 times higher than WSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> device without graphene, respectively. These results contribute to offer a novel and versatile strategy for overcoming the performance limitation in van der Waals photodetector.

0.5T0.5R—An Ultracompact RRAM Cell Uniquely Enabled by van der Waals Heterostructures

Conventional designs of the extensively studied resistive-random access-memory (RRAM) cell involve one transistor and one RRAM-“1T1R,” i.e., two separate devices thereby constraining its integration density. In this work, we overcome this longstanding limitation by experimentally demonstrating a novel memory architecture that combines the 1T and 1R into a single hybrid device by uniquely leveraging both lateral and vertical van der Waals (vdW) heterostructures. This ultracompact device, which can be considered as a “0.5T0.5R” memory cell, reduces the device count by half-the first of its kind in RRAM technology history, and simultaneously allows higher lateral as well as vertical (3-D) integration density w.r.t. the conventional 1T1R architecture. The unique “smart” device that can retain information after power is turned off is structurally designed by utilizing a shared graphene edge-contact and resistively switchable hexagonal boron nitride ( h-BN) insulator. Aided by design optimization, record performance(10 ns switching-speed), energy- (~0.07 pJ/bit), and area-efficiency (smallest footprint among all reported vdW-material-based RRAM memory units), as well as great retention (10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> s) and endurance (>1000), benchmarked against current vdW-material-based RRAM devices, have been achieved by this 0.5T0.5R memory cell. Moreover, the RRAM's fine tunability with ultrashort pulsewidth, pulse amplitude, and gate voltage, enables synaptic plasticity and makes it an integrated three-terminal RRAM with considerable potential for neuromorphic and in-memory computing applications.

First-principles investigation of the valley and electrical properties of carbon-doped α-graphyne-like BN sheet* *Project supported by the Special Foundation for Theoretical Physics Research Program of China (Grant No. 11847065) and the Natural Science Foundation of Shanxi Province, China (Grant No. 201901D211115).

Based on ab initio density functional theory calculations, we demonstrate that two carbon-doped boron nitride analog of α-graphyne structures, B3C2N3 and BC6N monolayers, are two-dimensional direct wide band gap semiconductors, and there are two inequivalent valleys in the vicinities of the vertices of their hexagonal Brillouin zones. Besides, B3C2N3 and BC6N monolayers exhibit relatively high carrier mobilities, and their direct band gap feature is robust against the biaxial strain. More importantly, the energetically most favorable B3C2N3 and BC6N bilayers also have direct wide band gaps, and valley polarization could be achieved by optical helicity. Finally, we show that BC6N monolayer might have high efficiency in photo-splitting reactions of water, and a vertical van der Waals heterostructure with a type-II energy band alignment could be designed using B3C2N3 and BC6N monolayers. All the above-mentioned characteristics make B3C2N3 and BC6N monolayers, bilayers, and their heterostructures recommendable candidates for applications in valleytronic devices, metal-free photocatalysts, and photovoltaic cells.

Halide Perovskite Epitaxial Heterostructures

ConspectusThe past decade has witnessed the great success and rapid development of halide perovskite materials in photovoltaics and light-emitting devices, which is due to the inherently high photoluminescence quantum yield, long carrier diffusion length, high light absorption coefficient, great defect tolerance, and remarkable tunability. For example, the record efficiency of perovskite solar cells has ramped up to 25.5%, comparable to single-crystal silicon solar cells. In combination with the facile solution processing, perovskite solar cells have gained tremendous attention and interest from both academia and the photovoltaic market. Moreover, as a newly emerging class of semiconductors with excellent properties and low manufacturing cost, it is also promising and meaningful to explore new applications beyond optoelectronic devices, such as transistors, lasers, and memory devices. To this end, the integration of different halide perovskites into epitaxial heterostructures provides an ideal option. On the other hand, from the perspective of fundamental studies, halide perovskite heterostructures also provide a platform to directly visualize ion migration and to study the charge transfer behavior and anomalous exciton phenomena, etc.The aim of our Account is to summarize the synthetic strategies to achieve halide perovskite epitaxial heterostructures and to highlight the effective routes to stabilize halide perovskites and heterostructures. We focus this Account on two-dimensional (2D) halide perovskites and emphasize the important roles the organic ligands play. Specifically, we discuss our recent findings on the incorporation of conjugated organic ligands into 2D halide perovskites leading to enhanced thermal and environmental stability and suppressed halide interdiffusion in the corresponding heterostructures. Molecular dynamics simulation and low-dose aberration corrected transmission electron microscopy were used as powerful tools to unveil and elucidate the working mechanism of stabilization and anion interdiffusion suppression. Following this strategy, diverse halide perovskite heterostructures between different halides, metals, or organic cations and more complex heterostructures and superlattices can be realized. Due to the reduced ion motion and improved stability, the interface of the heterostructures can be kept quite sharp. In the outlook of this Account, we discuss the challenges and a few promising directions with a special focus on the vertical van der Waals (vdW) heterostructures, which are expected to offer more flexibility in heterostructure integration and more opportunities in studying the charge transfer and carrier interaction along the out-of-plane direction. Moreover, the existence of semiconducting organic ligands provides new insights to tune the carrier and exciton behaviors along both in-plane and out-of-plane directions.

Stacking of 2D Materials

Abstract2D layered materials have sparked great interest from the perspective of basic physics and applied science in the past few years. Extraordinarily, many novel stacked structures that bring versatile properties and applications can be artificially assembled, as exemplified by vertical van der Waals (vdW) heterostructures, twisted multilayer 2D materials, hybrid dimensional structures, etc. Compared with the ordinary synthesis process, the stacking technique is a powerful strategy to achieve high‐quality and freely controlled 2D material stacked structures with atomic accuracy. This review highlights the most advanced stacking techniques involving the preparation, transfer, and stacking of high‐quality single crystal 2D materials. Apart from the 2D–2D stacked structures, 2D–0D, 2D–1D, and 2D–3D structures offer a prospective platform for the increasing application of 2D materials. The assembly strategy and physical properties of these stacked structures strongly depend on the factors in the stacking process, including the surface quality, angle control, and sample size. In addition, comparative analysis tables on the techniques involved are also available. The summary of these strategies and techniques will hopefully provide a valuable reference for relevant work.

Emerging Magnetic Interactions in van der Waals Heterostructures.

Vertical van der Waals (vdWs) heterostructures based on layered materials are attracting interest as a new class of quantum materials, where interfacial charge-transfer coupling can give rise to fascinating strongly correlated phenomena. Transition metal chalcogenides are a particularly exciting material family, including ferromagnetic semiconductors, multiferroics, and superconductors. Here, we report the growth of an organic-inorganic heterostructure by intercalating molecular electron donating bis(ethylenedithio)tetrathiafulvalene into (Li,Fe)OHFeSe, a layered material in which the superconducting ground state results from the intercalation of hydroxide layer. Molecular intercalation in this heterostructure induces a transformation from a paramagnetic to spin-glass-like state that is sensitive to the stoichiometry of molecular donor and an applied magnetic field. Besides, electron-donating molecules reduce the electrical resistivity in the heterostructure and modify its response to laser illumination. This hybrid heterostructure provides a promising platform to study emerging magnetic and electronic behaviors in strongly correlated layered materials.

Stable C2N/h-BN van der Waals heterostructure: flexibly tunable electronic and optic properties

Monolayer C2N has been successfully synthesized. To explore the enhancement of its stability and the expansion of its potential applications in electronics and optoelectronics, a vertical van der Waals heterostructure is constructed by C2N monolayer integrated with h-BN monolayer. The first-principles calculations based on the density functional theory show that this structure possesses a type-II band alignment with a smaller direct band gap and lager band offsets, suggesting that photo-generated electron–hole pairs can be well spatially separated, and thus an excellent photoelectric and photovoltaic material can be obtained. Also shown is that the electronic properties of such a heterostructure can be effectively regulated by a vertical strain and external electric field. For example, under compressive strain or forward electric field, its band gap can be significantly reduced to enhance light-excitation electron transition further, meanwhile the feature of direct band-gap and large band offsets is always well-preserved. Furthermore, it is found that the intrinsic heterostructure holds a wide optic adsorption range and large adsorption coefficient, and the applied compressive strain or a positive electric field can lead to a wide and high main absorption peak across the near-infrared, visible light, and ultraviolet region, implying that a tuned heterostructure has more promising applications in optoelectronics.

High-performance junction field-effect transistor based on black phosphorus/β-Ga2O3 heterostructure

Black phosphorous (BP), an excellent two-dimensional (2D) monoelemental layered p-type semiconductor material with high carrier mobility and thickness-dependent tunable direct bandgap structure, has been widely applied in various devices. As the essential building blocks for modern electronic and optoelectronic devices, high quality PN junctions based on semiconductors have attracted widespread attention. Herein, we report a junction field-effect transistor (JFET) by integrating narrow-gap p-type BP and ultra-wide gap n-type β-Ga2O3 nanoflakes for the first time. BP and β-Ga2O3 form a vertical van der Waals (vdW) heterostructure by mechanically exfoliated method. The BP/β-Ga2O3 vdW heterostructure exhibits remarkable PN diode rectifying characteristics with a high rectifying ratio about 107 and a low reverse current around pA. More interestingly, by using the BP as the gate and β-Ga2O3 as the channel, the BP/β-Ga2O3 JFET devices demonstrate excellent n-channel JFET characteristics with the on/off ratio as high as 107, gate leakage current around as low as pA, maximum transconductance (gm) up to 25.3 µS and saturation drain current (IDSS) of 16.5 µA/µm. Moreover, it has a pinch-off voltage of –20 V and a minimum subthreshold swing of 260 mV/dec. These excellent n-channel JFET characteristics will expand the application of BP in future nanoelectronic devices.