Van Der Waals Heterojunctions Research Articles

Gain-type photodetector with GFET-coupled MoS2/WSe2 heterojunction

Due to its exceptional photovoltaic properties and freedom from crystal lattice matching constraints, transition-metal dichalcogenides (TMDCs) have gained increased attention as a prospective two-dimensional (2D) layered material. Van der Waals heterojunctions (vdWHs) constituted of these materials afford chances for the advancement of high-performance photodetectors and solar cells. However, low light absorption efficiency and electron/hole traps at heterointerfaces make it difficult to improve the response speed and sensitivity of TMDCs vdWH based photodetectors. Here, we designed and realized a GFET-coupled MoS2/WSe2 heterojunction gain photodetector. An interfacial amplification effect is induced when a graphene field-effect transistor (GFET) is coupled to a MoS2/WSe2 heterojunction because of the lengthy carrier lifetime of MoS2 and the ultrahigh mobility of graphene. This effect leads to a high gain for our device, enhancing the photovoltaic response. Compared to the pristine MoS2/WSe2 heterojunction, the device exhibits two to three orders of magnitude improvement in responsivity, up to 50 A/W. Rising and decaying times of 67 μs and 2 μs are also achieved, respectively. By utilizing the strong correlation between the incident light spot position and the photocurrent, the device also enables sensitive detection of the spot position. This research offers an attainable method for developing gain-type, high-speed photodetectors.

Triazine-based covalent organic framework/ g-C3N4 heterojunction toward highly efficient photoactivation of peroxydisulfate for sulfonamides degradation

Rational design of multifunctional catalysts to realize the synergistic combination of photocatalysis and peroxydisulfate (PDS) activation process is a promising approach for the effective removal of recalcitrant pollutants. Herein, metal-free covalent organic framework/g-C3N4 (COF/CN) van der Waals heterojunction was synthesized by the in-situ polymerization on g-C3N4. The van der Waals force and π-π conjugation effect contributes to promoting the interfacial migration and separation of photoinduced carries. The photocatalytic removal efficiency of sulfamethazine (SMT) by COF/CN was increased by 4.9 and 6.6-folds compared to those of COF and g-C3N4, respectively. In the optimal COF/CN-3/PDS/Vis process, SO4•− and 1O2 were identified as the major contributors to SMT degradation. The relationship between the molecular reactivity of sulfonamides (SAs) and reaction kinetics was elucidated by density functional theory (DFT) calculations at the electron level. The degradation rates and pathways depend on the electronic distribution and reactive sites of SAs with five- or six-membered heterocyclic ring substituents. The nonradical attack on the aniline and the breakage of C-N bond were the common traits of SAs degradation, whereas a unique Smiles-type pathway occurred in SAs with six-membered heterocyclic substituents. This work expected to promote the insight for the interaction between molecular structures of pollutants and reactive species in wastewater purification.

Research on the robust electrical contact properties and favorable transport characteristics of two-dimensional WB4/MoSi2N4 van der Waals heterostructures

Ensuring optimal interface contact performance is crucial for achieving low-resistance ohmic contact in the design of two-dimensional (2D) electronic devices. In this study, we systematically investigate the contact properties of van der Waals (vdW) heterojunctions formed by compositing the semi-metal WB4 with Dirac cones and the semiconductor MoSi2N4 through first-principles calculations. A thorough investigation has been carried out on the electronic structure and transport characteristics at the interface. Our research findings indicate that the WB4/MoSi2N4 combination demonstrates robust ohmic contact performance, maintaining ohmic or near-ohmic p-type Schottky contacts over a wide range when exposed to electric field, varying layer spacing, and biaxial strain. This unique characteristic is associated with the Fermi level pinning (FLP), where there are gap states present at the interface. Here, the FLP plays a positive role in maintaining ohmic contact. In addition, different derivatives of MoSi2N4 are combined with WB4 to create heterostructures and study the changes in contact performance. Our research shows that the robust ohmic contact of WB4/MoSi2N4 will have excellent prospects for application in future electronic devices.

First principles study on the type-II g-C6N6/PtSSe heterojunction: A potential photocatalyst for overall water splitting

Constructing suitable van der Waals heterojunction is considered to be an efficient way to develop and design new multifunctional devices. In this work, DFT calculations have been preformed to investigate the stacking structures, electronic, optical as well as catalytic properties of vertical heterojunctions (g-C6N6/PtSSe) constructed from graphene-like C6N6 layer and PtSSe monolayer. It is predicted that Se-side contacted heterojunction (CN/SePtS) is a typical type-II semiconductor with band edges satisfying the conditions of overall water splitting, thus can be a potential photocatalyst. In addition, CN/SePtS also possesses good absorption ranging from ultraviolet to visible light regions. It is also found that strain engineering can further tune the electronic and optical properties of the heterojunction and even improve its visible light absorption. By considering the effect of optical driving force, CN/SePtS heterojunction with 4 % biaxial tensile strain is recommended to be a good candidate for overall water splitting photocatalyst. Our research can provide a guidance for designing new optoelectronic devices and photocatalysts based on g-C6N6/PtSSe vdW heterojunctions.

Monomolecular Membrane-Assisted Growth of Antimony Halide Perovskite/MoS2 Van der Waals Epitaxial Heterojunctions with Long-Lived Interlayer Exciton.

Epitaxial growth stands as a key method for integrating semiconductors into heterostructures, offering a potent avenue to explore the electronic and optoelectronic characteristics of cutting-edge materials, such as transition metal dichalcogenide (TMD) and perovskites. Nevertheless, the layer-by-layer growth atop TMD materials confronts a substantial energy barrier, impeding the adsorption and nucleation of perovskite atoms on the 2D surface. Here, we epitaxially grown an inorganic lead-free perovskite on TMD and formed van der Waals (vdW) heterojunctions. Our work employs a monomolecular membrane-assisted growth strategy that reduces the contact angle and simultaneously diminishing the energy barrier for Cs3Sb2Br9 surface nucleation. By controlling the nucleation temperature, we achieved a reduction in the thickness of the Cs3Sb2Br9 epitaxial layer from 30 to approximately 4 nm. In the realm of inorganic lead-free perovskite and TMD heterojunctions, we observed long-lived interlayer exciton of 9.9 ns, approximately 36 times longer than the intralayer exciton lifetime, which benefited from the excellent interlayer coupling brought by direct epitaxial growth. Our research introduces a monomolecular membrane-assisted growth strategy that expands the diversity of materials attainable through vdW epitaxial growth, potentially contributing to future applications in optoelectronics involving heterojunctions.

High-Spike Barrier Photodiodes Based on 2D Te/WS2 Heterostructures.

Two-dimensional (2D) van der Waals (vdWs) heterojunctions have been actively investigated in low-power-consumption and fast-response photodiodes owing to their atomically smooth interfaces and ultrafast interfacial charge transfer. However, achieving ultralow dark current and ultrafast photoresponse in the reported photovoltaic devices remains a challenge as the large built-in electric field in a heterojunction can not only speed up photocarrier transport but also increase the minority-carrier dark current. Here, we propose a high-spike barrier photodiode that can achieve both an ultralow dark current and an ultrafast response. The device is fabricated by the Te/WS2 heterojunction, while the band alignment can transition from type-II to type-I with a high electron barrier and a large hole built-in electronic field. The high electron barrier can greatly reduce the drift current of minority carriers and the generation current of the thermal carriers, while the large built-in electronic field can still speed up the photocarrier transport. The designed Te/WS2 vdWs photodiode yields an ultralow dark current of 8 × 10-14 A and an ultrafast photoresponse of 10/13 μs. Furthermore, a high-performance visible-light imager with a pixel resolution of 100 × 40 is demonstrated using the Te/WS2 vdWs photodiode. This work provides a comprehensive understanding of designing 2D-material-based photovoltaics with excellent overall performance.

Programmable Interfacial Band Configuration in WS2/Bi2O2Se Heterojunctions.

van der Waals heterojunctions based on transition-metal dichalcogenides (TMDs) offer advanced strategies for manipulating light-emitting and light-harvesting behaviors. A crucial factor determining the light-material interaction is in the band alignment at the heterojunction interface, particularly the distinctions between type-I and type-II alignments. However, altering the band alignment from one type to another without changing the constituent materials is exceptionally difficult. Here, utilizing Bi2O2Se with a thickness-dependent band gap as a bottom layer, we present an innovative strategy for engineering interfacial band configurations in WS2/Bi2O2Se heterojunctions. In particular, we achieve tuning of the band alignment from type-I (Bi2O2Se straddling WS2) to type-II and finally to type-I (WS2 straddling Bi2O2Se) by increasing the thickness of the Bi2O2Se bottom layer from monolayer to multilayer. We verified this band architecture conversion using steady-state and transient spectroscopy as well as density functional theory calculations. Using this material combination, we further design a sophisticated band architecture incorporating both type-I (WS2 straddles Bi2O2Se, fluorescence-quenched) and type-I (Bi2SeO5 straddles WS2, fluorescence-recovered) alignments in one sample through focused laser beam (FLB). By programming the FLB trajectory, we achieve a predesigned localized fluorescence micropattern on WS2 without changing its intrinsic atomic structure. This effective band architecture design strategy represents a significant leap forward in harnessing the potential of TMD heterojunctions for multifunctional photonic applications.

Construction of covalent organic framework and g-C3N4 heterojunction for photocatalytic degradation of tetracycline and photocatalytic production of hydrogen peroxide

Organic semiconductors, notably graphitic carbon nitride (g-C3N4, CN), are increasingly recognized as effective photocatalysts for environmental remediation and energy harvesting. In this study, we introduce a Van der Waals metal-free heterojunction (TTO/CN), composed of g-C3N4 and a vinyl-linked covalent organic framework (COF), fabricated via a simple self-assembly process. This novel heterojunction is adeptly utilized for the photocatalytic degradation of tetracycline (TC) in aqueous environments and for the generation of hydrogen peroxide (H2O2). The synthesized TTO/CN heterojunction demonstrates an expanded specific surface area and broadened absorption spectrum in the visible light range, coupled with enhanced efficiency in photogenerated carrier separation and transfer. These attributes collectively contribute to its remarkable photocatalytic performance. Notably, the TTO/CN-1 variant emerges as a highly efficient photocatalyst, exhibiting degradation rate constants for TC that surpass those of TTO-COF and CN by 2.0 and 6.2 times, respectively. Furthermore, TTO/CN-1 distinguishes itself as a dual-functional photocatalyst, showcasing exceptional activity in H2O2 production (745.3 μM·h−1, or 1863.3 μmol·g−1·h−1). This research heralds a potent strategy for the design and synthesis of van der Waals heterojunction photocatalysts, and the distinctive heterostructures of COF and CN hold significant promise for enhancing the performance and broadening the applicability of CN-based photocatalysts.

Polarized Photodetectors Based on 2D 2H‐MoTe2/1T'‐MoTe2/MoSe2 Van Der Waals Heterojunction

AbstractThe van der Waals heterojunction based on transition metal dichalcogenides has broad research value and application prospects as the basic material for advanced near‐infrared polarized photodetectors. a type II heterojunction based on the 2H‐MoTe2/1T′‐MoTe2/MoSe2 structure is reported for photovoltaic photodetectors. Notably, this device generates a self‐powered photocurrent, eliminating the need for an external bias or gate voltage. This device has the ability to detect polarized light, and its photocurrent anisotropy ratio is 55. The device performance is significantly amplified due to the proficient facilitation of electron‐hole separation through the type II band structure of MoSe2 at the bottom and 2H‐MoTe2 at the top, as well as enhanced exciton splitting by 1T′‐MoTe2 situated in the middle. Consequently, the device demonstrates exceptional proficiency, presenting a noteworthy response rate of 0.76 A W−1, a high detection rate of 3 × 109 Jones, an elevated EQE of 71%, and rapid rising and falling response speeds of 13 ms/10 ms respectively. Moreover, the device's anisotropy ratio of photocurrent highlights its sensitivity to polarized light, making it a promising candidate for applications in polarized photodetection. Overall, this innovative heterostructure opens new avenues for exploring and developing advanced optoelectronic devices based on 2D van der Waals materials.

Multifunction realization in MoS2/WS2/h-BN heterojunction: Integrated self-powered high-performance photodetection, visualization, nonvolatile memory, and synaptic simulation

Nowadays, efficient performance, functional diversification, device miniaturization and systematic integration are the trends for developing new electronic information technology. However, photodetectors with only optoelectronic detection functions cannot satisfy the growing demands of the multifunction required in single devices. This paper presents a MoS2/WS2/h-BN van der Waals heterojunction device realizing multifunctional applications which integrated self-powered high-performance photodetection, visualization, nonvolatile memory, and synaptic simulation. The heterojunction achieves a high responsivity of 9.28 A/W, an excellent specific detectivity of 6.1×1012 Jones, a large external quantum efficiency of 2358 %, a considerable on/off ratio of 7×105 and an ultrafast response time of 0.6 μs at 1 V bias under 488 nm laser irradiation. Besides, the photodetector shows excellent photovoltaic characteristics with a short-circuit current of 0.22 μA and an open-circuit voltage of 0.34 V. Moreover, the device also shows a favorable optical response to 532 and 633 nm lasers. The device also realizes visualization and can be used as an imaging sensor. In addition, the device integrates nonvolatile memory function due to the charge storage effect of h-BN and h-BN/SiO2 interface. Furthermore, biological synaptic functions, such as the memory process, short- and long-term plasticity, and double pulse facilitation, are also successfully simulated. This work realizes the high-performance and multifunctional applications of MoS2/WS2/h-BN device based on a new strategy of utilizing h-BN as a heterojunction substrate.

Van der Waals heterojunctions comprising double/single-walled carbon nanotubes: Insights into heat flux and thermal rectification

Van der Waals (vdWs) heterojunctions constructed from double/single-walled carbon nanotubes (DSCNTs) demonstrate exceptional thermal rectification (TR) ratios, coupled with a straightforward fabrication process, making them highly suitable for thermal rectifier applications. In this study, we employed a Nonequilibrium Molecular Dynamics method to investigate the heat flux and TR across DSCNTs with varying interlayer spacings. Our findings reveal that at smaller interlayer spacings, high temperatures readily overcome vdWs interactions. Conversely, increasing the interlayer spacing initially impedes this effect, though elevated temperatures can surmount this barrier. Significantly, at specific combinations of temperature and interlayer spacing, the left side in DSCNTs establishes interlayer phonons transport channels, facilitating forward heat flux but impeding the backward. This mechanism results in an exceptionally high TR ratio, reaching up to 757 %. Additionally, altering the chiral configurations of the CNTs in the inner and outer layers, while preserving interlayer spacing, further enhances the TR ratio and reduces the temperature threshold required to achieve peak TR ratio. Our findings contribute valuable insights into the phonon transport mechanisms within one-dimensional vdWs heterojunctions.

Low-cost and efficient all group-IV visible/shortwave infrared dual-band photodetector.

Low-cost broadband photodetectors (PDs) based on group-IV materials are highly demanded. Herein, a vertical all group-IV graphene-i-n (Gr-i-n) structure based on sputtering-grown undoped Ge0.92Sn0.08/Ge multiple quantum wells (MQWs) on n-Ge substrate was proposed to realize efficient visible/shortwave infrared (VIS/SWIR) dual-band photoresponse. Harnessing Gr-germanium tin (GeSn)/Ge MQWs van der Waals heterojunctions, an extended surface depletion region was established, facilitating separation and transportation of photogenerated carriers at VIS wavelengths. Consequently, remarkable VIS/SWIR dual-band response ranging from 400 to 2000 nm with a rapid response time of 23 μs was achieved. Compared to the PD without Gr, the external quantum efficiency at 420, 660, and 1520 nm was effectively enhanced by 10.2-, 5.2-, and 1.2-fold, reaching 40, 42, and 50%, respectively. This research paves the way for the advancement of all group-IV VIS/SWIR broadband PDs and presents what we believe to be a novel approach to the design of low-cost broadband PDs.

GeC/SiCx van der Waals heterojunction: Applications for water splitting and solar cell

We construct GeC/SiCx(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/SiC7 heterojunctions fulfill the requirements as photocatalysts from PH = 0 to PH = 14. Although the GeC/SiC2 heterojunction fulfills the requirements as a photocatalyst from PH = 6 to PH = 10, the GeC/SiC2-based solar cell presents excellent performance, whose power conversion efficiency reaches 24.6 % theoretically. The results demonstrate that GeC/SiCx (x = 1, 2, 7) is a potential candidate for photocatalytic and solar cell materials in the future.

Tandem Fields Facilitating Directional Carrier Migration in Van der Waals Heterojunction for Efficient Overall Piezo-Synthesis of H2O2.

Piezo-synthesis of H2O2 utilizing sustainable mechanical energy as well as earth-abundant water and oxygen is a green, cost-effective, and promising approach. However, achieving simultaneous two-electron water oxidation reaction (2e- WOR) and two-electron oxygen reduction reaction (2e- ORR) faces huge challenges due to insufficient synergistic active sites and slow/messy carrier transfer. Herein, a novel 2D/2D van der Waals heterojunction consisting of BiOIO3 and carbon nitride (BIO/CN) is elaborately designed for highly efficient overall H2O2 piezo-synthesis. Theoretical/experimental results reveal that a Z-scheme electron transfer is formed and facilitated by the tandem interfacial electric field and the bulk piezo-polarization field. On this basis, the carriers are efficiently separated while the oxidation/reduction capacity is preserved, thus providing the strong driving force for the 2e- WOR and 2e- ORR on BIO and CN, respectively. Furthermore, the kinetic and thermodynamic processes of WOR and ORR for H2O2 synthesis improve remarkably. Therefore, BIO/CN exhibits an excellent H2O2 yield of 259.8µM within 30min in pure water and air atmosphere (without any sacrificial agents and aeration). This study provides a new idea on strategically controlling electron transfer toward high-efficiency H2O2 piezo-synthesis and expands the avenue for developing effective environmental purification materials.

Dual-function optical modulation and detection in microring resonators integrated graphene/MoTe2 heterojunction

On-chip photonic devices such as modulators and photodetectors are essential building blocks for integrated photonics, enabling a wide range of applications in optical communication, sensing, and other emerging fields. Generally, optical modulation and photodetection are accomplished by two discrete devices in integrated photonic circuits, prohibiting the expansion of device functionality and the miniaturization of photonic systems. In this work, we demonstrate graphene/MoTe2 heterojunction integrating with microring resonators (MRRs) to serve as an optical modulator under positive bias voltage and a photodetector under negative bias voltage at the telecom band. Such a device primarily benefits from graphene's optoelectronic characteristics, including broadband absorption and electrostatically tunable refractive index. The obtained dual-functional MoTe2/graphene heterojunction devices demonstrate a modulation depth of ∼26.7 dB, a bandwidth of 7.0 GHz, and a self-driven, wavelength-sensitive optoelectronic response at the telecom C band. Our studies indicate that combining graphene van der Waals heterojunction with MRRs paves the way to emerging photonic applications such as neuromorphic computing while expanding the freedom for miniaturized photonic circuits.

MoS2/MXene Van der Waals heterojunction-based electrochemiluminescence sensor for triple negative breast cancer detection

The van der Waals heterojunction is able to combine the advantages of different materials and has potential to be used in biosensing researches. In this study, we developed a novel van der Waals heterojunction by combining MXene and MoS2 nanosheets for the electrochemiluminescence (ECL) sensing applications. This van der Waals heterojunction material not only possessed the superior conductivity of MXene, but also regulated the electron transport. Additionally, the incorporation of MoS2 nanosheets into the MXene interlayers significantly enhances the material stability. Meanwhile, nitrogen-rich quantum dots (N dots) were synthesized as ECL tags with an impressive nitrogen content of up to 75 %. By integrating the ECL response of N dots within the van der Waals heterojunction, we established a highly efficient sensing system for miRNA-373, which overexpressed in triple negative breast cancer tissues. The van der Waals heterojunction-based biosensor can enhance the ECL signal of N dots effectively to detect miRNA-373 from 1 fM to 1 μM. Consequently, the developed sensing system holds promise for the early detection of metastasis of the triple-negative breast cancer, paving the way for the effective clinical interventions.

Schottky junction-mediated carrier separation in BiOBr/Ti3C2Tx van der Waals heterojunction photocatalyst for increased removal of Cr(VI) under visible-light

The photocatalytic removal of pollutants can integrate efficient solar energy utilization with wastewater treatment. Herein, we report a simple strategy to construct BiOBr/Ti3C2Tx composite photocatalysts consisting of self-assembled van der Waals (vdw) heterojunction structures containing Schottky junctions. The vdW interaction between BiOBr and Ti3C2Tx and the structural stability of the catalysts were validated by density functional theory (DFT) calculations and an ab initio molecular dynamic simulation (AIMD). Compared to BiOBr, the BiOBr/Ti3C2Tx composites exhibited an enhanced light absorption capability and photocurrent response, along with a lower carrier recombination rate and charge-transfer resistance. The BiOBr/Ti3C2Tx activity for the photoreduction of hexavalent chromium (Cr(VI)) under visible-light irradiation considerably surpassed that of the original BiOBr (53.9 %). Using the BTC-0.8 catalyst (with a Ti3C2Tx: BiOBr mass ratio of 0.8 %) optimal reduction efficiency (94.0 %) for Cr(VI) with a reaction rate approximately 3.5 times that of pure BiOBr. The BTC-0.8 catalyst was viable over a wide pH range and maintained an 83.9 % photoreduction rate after four cycling experiments. The exceptional photocatalytic ability of BiOBr/Ti3C2Tx was achieved because Ti3C2Tx served as an electron injection layer that separated photogenerated carriers. The Schottky junction constructed within the BiOBr/Ti3C2Tx vdW heterojunctions suppressed electron backflow, promoting carrier separation. The excellent photocatalytic performance and strong cyclic stability of BiOBr/Ti3C2Tx demonstrated the considerable application potential of this photocatalyst.

Two-Dimensional Sc2CCl2/XSe2(X=Mo, Pt) van der Waals Heterojunctions: Promising Photocatalytic Hydrogen Evolution Materials.

In the field of photocatalysis, new heterojunction materials are increasingly explored to achieve efficient energy conversion and environmental catalysis under visible light and sunlight. This paper presents a study on two newly constructed two-dimensional van der Waals heterojunctions, Sc2CCl2/MoSe2 and Sc2CCl2/PtSe2, using density-functional theory. The study includes a systematic investigation of their geometrical structure, electronic properties, and optical properties. The results indicate that both heterojunctions are thermodynamically, kinetically, and mechanically stable. Additionally, Bader charge analysis reveals that both heterojunctions exhibit typical type II band properties. However, the band gap of the Sc2CCl2/MoSe2 heterojunction is only 1.18 eV, which is insufficient to completely cross the reduction and oxidation (REDOX) potential of 1.23 eV, whereas the band gap of Sc2CCl2/PtSe2 heterojunction is 1.49 eV, which is theoretically capable for water decomposition. The subsequent calculation of the Sc2CCl2/PtSe2 heterojunction demonstrate excellent hole carrier mobility and high efficiency light absorption in the visible light range, facilitating the separation of photogenerated electrons and holes. More importantly, Sc2CCl2/PtSe2 vdW type II heterojunction can achieve full water decomposition from pH 1 to pH 4, and its thermodynamic feasibility is confirmed by Gibbs free energy results. The aim of this study is to develop materials and analyses that will result in optoelectronic devices that are more efficient, stable, and sustainable.

Electric field and strain tuned the electronic and optical properties of Zr2CO2/MoSe2 van der Waals heterojunction

Two-dimensional semiconductor materials have attracted significant research interest due to their exceptional properties in various applications. Among them, transition-metal dichalcogenides and MXenes have emerged as widely used materials in photoelectronic devices due to their excellent optical and electronic properties. In this study, we investigate the electronic and optical properties of MXene/MX2 heterojunctions by employing First Principles based on density functional theory calculations on Zr2CO2/MoSe2 van der Waals heterojunctions. The results of band structure, density of states and band alignment demonstrate that the Zr2CO2/MoSe2 heterojunction is a type-II band alignment with an indirect bandgap of 0.93 eV. We further explore the impact of electric fields and strains on their electronic and optical performance. The results show that carriers can be effectively separated for designing high-performance devices in photocatalysis under electric fields ranging from −0.5 to 0.5 V/Å and biaxial strains ranging from −4% to 10 %. The formation of the Zr2CO2/MoSe2 heterojunction allows for enhanced coefficient and a broader light absorption range compared to the individual Zr2CO2 and MoSe2 components. In consequence, this study contributes to a fundamental understanding of Zr2CO2/MoSe2 heterojunctions and their potential applications in photocatalysis.

Dominant n-type conduction and fast photoresponse in BP/MoS2 heterostructures

In recent years, van der Waals heterojunctions between two-dimensional (2D) materials have garnered significant attention for their unique electronic and optoelectronic properties and have opened avenues for innovative device architectures and applications. Among them, the heterojunction formed by black phosphorus (BP) and molybdenum disulfide (MoS2) stands out as a promising candidate for advanced optoelectronic devices. This study unravels the interplay between BP, MoS2, and Cr contacts to explain the electrical behavior of a BP/MoS2 heterojunction showing rectifying behavior with dominant n-type conduction, and a high ON/OFF current ratio around 104 at ± 20 V. The higher unexpected current observed when applying a negative bias to either MoS2 or BP side is elucidated by an energy band model incorporating a type II heterojunction at the BP/MoS2 interface with Cr forming a Schottky contact with MoS2 and an ohmic contact with BP. The BP/MoS2 heterojunction shows pronounced photoresponse, linearly dependent on the incident laser power, with a responsivity of 100 µA/W under white light at 50 µW incident power. Time-resolved photocurrent measurements reveal a relatively fast response with characteristic rise times less than 200 ms. This work demonstrates that BP/MoS2 van der Waals heterojunctions have unique electrical and photoresponse characteristics that are promising for advanced optoelectronic applications.