Showing papers on "Schottky barrier published in 2021"

Ultralow contact resistance between semimetal and monolayer semiconductors.

Abstract: Advanced beyond-silicon electronic technology requires both channel materials and also ultralow-resistance contacts to be discovered1,2. Atomically thin two-dimensional semiconductors have great potential for realizing high-performance electronic devices1,3. However, owing to metal-induced gap states (MIGS)4–7, energy barriers at the metal–semiconductor interface—which fundamentally lead to high contact resistance and poor current-delivery capability—have constrained the improvement of two-dimensional semiconductor transistors so far2,8,9. Here we report ohmic contact between semimetallic bismuth and semiconducting monolayer transition metal dichalcogenides (TMDs) where the MIGS are sufficiently suppressed and degenerate states in the TMD are spontaneously formed in contact with bismuth. Through this approach, we achieve zero Schottky barrier height, a contact resistance of 123 ohm micrometres and an on-state current density of 1,135 microamps per micrometre on monolayer MoS2; these two values are, to the best of our knowledge, the lowest and highest yet recorded, respectively. We also demonstrate that excellent ohmic contacts can be formed on various monolayer semiconductors, including MoS2, WS2 and WSe2. Our reported contact resistances are a substantial improvement for two-dimensional semiconductors, and approach the quantum limit. This technology unveils the potential of high-performance monolayer transistors that are on par with state-of-the-art three-dimensional semiconductors, enabling further device downscaling and extending Moore’s law. Electric contacts of semimetallic bismuth on monolayer semiconductors are shown to suppress metal-induced gap states and thus have very low contact resistance and a zero Schottky barrier height.

Self-Powered MXene/GaN van der Waals Heterojunction Ultraviolet Photodiodes with Superhigh Efficiency and Stable Current Outputs

Abstract: A self-powered, high-performance Ti3 C2 Tx MXene/GaN van der Waals heterojunction (vdWH)-based ultraviolet (UV) photodiode is reported. Such integration creates a Schottky junction depth that is larger than the UV absorption depth to sufficiently separate the photoinduced electron/hole pairs, boosting the peak internal quantum efficiency over the unity and the external quantum efficiency over 99% under weak UV light without bias. The proposed Ti3 C2 Tx /GaN vdWH UV photodiode demonstrates pronounced photoelectric performances working in self-powered mode, including a large responsivity (284 mA W-1 ), a high specific detectivity (7.06 × 1013 Jones), and fast response speed (rise/decay time of 7.55 µs/1.67 ms). Furthermore, the remarkable photovoltaic behavior leads to an impressive power conversion efficiency of 7.33% under 355 nm UV light illumination. Additionally, this work presents an easy-processing spray-deposition route for the fabrication of large-area UV photodiode arrays that exhibit highly uniform cell-to-cell performance. The MXene/GaN photodiode arrays with high-efficiency and self-powered ability show high potential for many applications, such as energy-saving communication, imaging, and sensing networks.

Interfacial engineering of Bi2S3/Ti3C2Tx MXene based on work function for rapid photo-excited bacteria-killing.

Abstract: In view of increasing drug resistance, ecofriendly photoelectrical materials are promising alternatives to antibiotics. Here we design an interfacial Schottky junction of Bi2S3/Ti3C2Tx resulting from the contact potential difference between Ti3C2Tx and Bi2S3. The different work functions induce the formation of a local electrophilic/nucleophilic region. The self-driven charge transfer across the interface increases the local electron density on Ti3C2Tx. The formed Schottky barrier inhibits the backflow of electrons and boosts the charge transfer and separation. The photocatalytic activity of Bi2S3/Ti3C2Tx intensively improved the amount of reactive oxygen species under 808 nm near-infrared radiation. They kill 99.86% of Staphylococcus aureus and 99.92% of Escherichia coli with the assistance of hyperthermia within 10 min. We propose the theory of interfacial engineering based on work function and accordingly design the ecofriendly photoresponsive Schottky junction using two kinds of components with different work functions to effectively eradicate bacterial infection. MXenes have emerged as potential antimicrobial materials. Here, the authors report on the creation of a Schottky junction to increase the charge separation between MXenes and semiconductor to increase photodynamic creation of reactive oxygen species under near infrared irradiation for antibacterial purposes.

Synthesis of 2D/2D CoAl-LDHs/Ti3C2Tx Schottky-junction with enhanced interfacial charge transfer and visible-light photocatalytic performance

Abstract: The layered double hydroxides (LDHs) are potential non-noble metal photocatalysts. Unfortunately, the intrinsic activity of bulk LDHs is relatively low, which limits their use. Herein, the ultrathin, porous and vacancy-rich CoAl-LDHs nanosheets were prepared by exfoliation strategy. Then, they were assembled with the early transition-metal carbides nanosheets (MXenes, Ti3C2Tx) to afford a hybrid 2D/2D CoAl-LDHs/Ti3C2Tx photocatalyst via electrostatic assembly process. The experiments indicated that the CoAl-LDHs/Ti3C2Tx hybrids performed an excellent visible-light photocatalytic activity for tetracycline hydrochloride (96.67 %) degradation. Diversified characterization techniques (SEM, TEM, AFM, N2 adsorption-desorption analysis, XRD, FTIR, UV–vis DRS, photoelectrochemical test) and density functional theory calculations (electronic and optical properties) have indicated that such excellent photocatalytic activity was ascribed to the synergy and the Schottky heterojunction formation between CoAl-LDHs nanosheets and Ti3C2Tx nanosheets, which possessed markedly visible-light absorption, high specific surface area, rapid electrons transfer and depressed electron-hole pairs recombination.

Highly sensitive solar-blind deep ultraviolet photodetector based on graphene/PtSe2/β-Ga2O3 2D/3D Schottky junction with ultrafast speed

Abstract: There is an emerging need for high-sensitivity solar-blind deep ultraviolet (DUV) photodetectors with an ultra-fast response speed. Although nanoscale devices based on Ga2O3 nanostructures have been developed, their practical applications are greatly limited by their slow response speed as well as low specific detectivity. Here, the successful fabrication of two-/three-dimensional (2D/3D) graphene (Gr)/PtSe2/β-Ga2O3 Schottky junction devices for high-sensitivity solar-blind DUV photodetectors is demonstrated. Benefitting from the high-quality 2D/3D Schottky junction, the vertically stacked structure, and the superior-quality transparent graphene electrode for effective carrier collection, the photodetector is highly sensitive to DUV light illumination and achieves a high responsivity of 76.2 mA/W, a large on/off current ratio of ~ 105, along with an ultra-high ultraviolet (UV)/visible rejection ratio of 1.8 × 104. More importantly, it has an ultra-fast response time of 12 µs and a remarkable specific detectivity of ~ 1013 Jones. Finally, an excellent DUV imaging capability has been identified based on the Gr/PtSe2/β-Ga2O3 Schottky junction photodetector, demonstrating its great potential application in DUV imaging systems.

Evidencing Interfacial Charge Transfer in 2D CdS/2D MXene Schottky Heterojunctions toward High-Efficiency Photocatalytic Hydrogen Production

Abstract: Photocatalytic water splitting by heterojunction nanostructures is considered as one of the most favorable pathways for direct solar-to-hydrogen conversion. High-efficiency solar hydrogen production demands an effective separation of charge carriers and their rapid transport to the interface, whereas the charge-transfer pathway in heterojunction photocatalysts is largely elusive. Herein, 2D CdS/2D MXene Schottky heterojunctions are synthesized via a sequence of electrostatic self-assembly process and solvothermal method. The composite photocatalysts exhibit highly efficient and robust hydrogen-evolving performance, far superior than the pristine CdS nanosheets. Furthermore, density functional theory (DFT) calculations are adopted to unveil the charge-transport pathway. It is revealed that an intimate Schottky contact is constructed between CdS and MXene, which further steers the formation of charge flow and expedites the charge migration from CdS to MXene, thus suppressing the recombination of photogenerated charge carriers and boosting the photocatalytic activity for hydrogen evolution.

Gate-controlled reversible rectifying behavior investigated in a two-dimensional MoS 2 diode

Abstract: By using density functional theory and ab initio quantum-transport simulation, we study the Schottky barrier and the rectifying behavior of diodes consisting of the two-dimensional metal phase $1T\text{\ensuremath{-}}{\mathrm{MoS}}_{2}$ and semiconductor phase 2H-${\mathrm{MoS}}_{2}$. The results show that the Schottky barrier of the out-of-plane (OP) contacted ${\mathrm{MoS}}_{2}$ heterostructure diode is a little different from that of the in-plane (IP) contacted ${\mathrm{MoS}}_{2}$ heterostructure diode. The current-voltage characteristics show that the OP diode has the better rectifying behavior compared to the IP diode under the zero gate voltage. The corresponding maximum rectifier ratio of the OP Schottky barrier diode is close to ${10}^{7}$ at 0.9 V bias voltage. More interestingly, we find that the gate voltage can be used to effectively control the rectifying behavior of the two diodes. The positive gate voltages can increase the current value of two Schottky barrier diodes, but weaken their rectification ratios. The negative gate voltages can reverse the rectifying direction of two Schottky barrier diodes. The above results provide good theoretical guidance for the designing of diode devices based on two-dimensional materials in the future.

Schottky barrier heights in two-dimensional field-effect transistors: from theory to experiment.

Abstract: Over the past decade, two-dimensional semiconductors (2DSCs) have aroused wide interest due to their extraordinary electronic, magnetic, optical, mechanical, and thermal properties, which hold potential in electronic, optoelectronic, thermoelectric applications, and so forth. The field-effect transistor (FET), a semiconductor gated with at least three terminals, is pervasively exploited as the device geometry for these applications. For lack of effective and stable substitutional doping techniques, direct metal contact is often used in 2DSC FETs to inject carriers. A Schottky barrier (SB) generally exists in the metal-2DSC junction, which significantly affects and even dominates the performance of most 2DSC FETs. Therefore, low SB or Ohmic contact is highly preferred for approaching the intrinsic characteristics of the 2DSC channel. In this review, we systematically introduce the recent progress made in theoretical prediction of the SB height (SBH) in the 2DSC FETs and the efforts made both in theory and experiments to achieve low SB contacts. From the comparison between the theoretical and experimentally observed SBHs, the emerging first-principles quantum transport simulation turns out to be the most powerful theoretical tool to calculate the SBH of a 2DSC FET. Finally, we conclude this review from the viewpoints of state-of-the-art electrode designs for 2DSC FETs.

Ohmic Contact Engineering for Two-Dimensional Materials

Abstract: Summary One of the major areas of semiconductor device research is the development of transparent or ohmic contacts between semiconductors and metal electrodes for the efficient injection of charge carriers into the conduction channel. Fast-emerging two-dimensional (2D) materials with atomically flat surfaces, free of dangling bonds, are intuitively promising to form ohmic contacts with metals. However, the contacts of 2D devices usually possess a large Schottky barrier and rarely follow the Schottky-Mott rule, because of interfacial effects such as Fermi-level pinning. Herein, we summarize recent progress and developments in contact engineering of 2D materials for the realization of ohmic contacts in 2D electronic devices. The basic physics of contacts for both Si and 2D materials is briefly introduced. A variety of engineering strategies are subsequently introduced, including band matching, doping, phase engineering, insertion of buffer layers, 2D/metal van der Waals contacts, and edge contacts. Finally, opportunities and challenges for optimizing contacts for future 2D electronics are discussed.

Enhanced bulk photovoltaic effect in two-dimensional ferroelectric CuInP2S6.

Abstract: The photocurrent generation in photovoltaics relies essentially on the interface of p-n junction or Schottky barrier with the photoelectric efficiency constrained by the Shockley-Queisser limit. The recent progress has shown a promising route to surpass this limit via the bulk photovoltaic effect for crystals without inversion symmetry. Here we report the bulk photovoltaic effect in two-dimensional ferroelectric CuInP2S6 with enhanced photocurrent density by two orders of magnitude higher than conventional bulk ferroelectric perovskite oxides. The bulk photovoltaic effect is inherently associated to the room-temperature polar ordering in two-dimensional CuInP2S6. We also demonstrate a crossover from two-dimensional to three-dimensional bulk photovoltaic effect with the observation of a dramatic decrease in photocurrent density when the thickness of the two-dimensional material exceeds the free path length at around 40 nm. This work spotlights the potential application of ultrathin two-dimensional ferroelectric materials for the third-generation photovoltaic cells. While magnetism, hyperferroelectricity, and topological phases in the two-dimensional limit have been widely explored, the direct experimental study on bulk photovoltaic effect in 2D materials remains unimplemented. Here, the authors find bulk photovoltaic effect in 2D ferroelectric CuInP2S6.

Near-ideal van der Waals rectifiers based on all-two-dimensional Schottky junctions.

Abstract: The applications of any two-dimensional (2D) semiconductor devices cannot bypass the control of metal-semiconductor interfaces, which can be severely affected by complex Fermi pinning effects and defect states. Here, we report a near-ideal rectifier in the all-2D Schottky junctions composed of the 2D metal 1 T′-MoTe2 and the semiconducting monolayer MoS2. We show that the van der Waals integration of the two 2D materials can efficiently address the severe Fermi pinning effect generated by conventional metals, leading to increased Schottky barrier height. Furthermore, by healing original atom-vacancies and reducing the intrinsic defect doping in MoS2, the Schottky barrier width can be effectively enlarged by 59%. The 1 T′-MoTe2/healed-MoS2 rectifier exhibits a near-unity ideality factor of ~1.6, a rectifying ratio of >5 × 105, and high external quantum efficiency exceeding 20%. Finally, we generalize the barrier optimization strategy to other Schottky junctions, defining an alternative solution to enhance the performance of 2D-material-based electronic devices. Here, a defect healing method is used to tune the height and width of the Schottky barrier at the interface between 2D metals and 2D semiconductors, leading to the realization of van der Waals rectifiers with enhanced performance.

Efficient Ohmic contacts and built-in atomic sublayer protection in MoSi2N4 and WSi2N4 monolayers

Abstract: Metal contacts to two-dimensional (2D) semiconductors are often plagued by the strong Fermi level pinning (FLP) effect which reduces the tunability of the Schottky barrier height (SBH) and degrades the performance of 2D semiconductor devices. Here, we show that MoSi2N4 and WSi2N4 monolayers—an emerging 2D semiconductor family with exceptional physical properties—exhibit strongly suppressed FLP and wide-range tunable SBH. An exceptionally large SBH slope parameter of S ≈ 0.7 is obtained which outperforms the vast majority of other 2D semiconductors. Such intriguing behavior arises from the septuple-layered morphology of MoSi2N4 and WSi2N4 monolayers in which the semiconducting electronic states are protected by the outlying Si–N sublayer. We identify Ti, Sc, and Ni as highly efficient Ohmic contacts to MoSi2N4 and WSi2N4 with zero interface tunneling barrier. Our findings reveal the potential of MoSi2N4 and WSi2N4 as a practical platform for designing high-performance and energy-efficient 2D semiconductor electronic devices.

Packaged Ga 2 O 3 Schottky Rectifiers With Over 60-A Surge Current Capability

Abstract: Ultrawide-bandgap gallium oxide (Ga2O3) devices have recently emerged as promising candidates for power electronics; however, the low thermal conductivity ( k T) of Ga2O3 causes serious concerns about their electrothermal ruggedness. This letter presents the first experimental demonstrations of large-area Ga2O3 Schottky barrier diodes (SBDs) packaged in the bottom-side-cooling and double-side-cooling configurations, and for the first time, characterizes the surge current capabilities of these packaged Ga2O3 SBDs. Contrary to popular belief, Ga2O3 SBDs with proper packaging show high surge current capabilities. The double-side-cooled Ga2O3 SBDs with a 3 × 3-mm2 Schottky contact area can sustain a peak surge current over 60 A, with a ratio between the peak surge current and the rated current superior to that of similarly-rated commercial SiC SBDs. The key enabling mechanisms for this high surge current are the small temperature dependence of on -resistance, which strongly reduces the thermal runaway, and the double-side-cooled packaging, in which the heat is extracted directly from the Schottky junction and does not need to go through the low- k T bulk Ga2O3 chip. These results remove some crucial concerns regarding the electrothermal ruggedness of Ga2O3 power devices and manifest the significance of their die-level thermal management.

Carbon Vacancy Mediated Incorporation of Ti3C2 Quantum Dots in a 3D Inverse Opal g-C3N4 Schottky Junction Catalyst for Photocatalytic H2O2 Production

Abstract: Photocatalytic H2O2 production is an environmentally friendly and sustainable production technique. Here, we fabricate the Ti3C2 quantum dot-modified defective inverse opal g-C3N4 (TC/CN) via a fac...

Recent developments in the photodetector applications of Schottky diodes based on 2D materials

Abstract: In recent years, 2D layered materials have emerged as potential candidates in the opto-electronic field due to their intriguing optical, electrical and mechanical properties. Photodetectors based on 2D materials have been reported to exhibit excellent photodetection capability due to their tunable bandgap and ability to detect broadband spectrum ranging from UV to NIR. Schottky junction-based detectors are highly sensitive and fast responsive compared to other heterojunction devices. Schottky contacted devices are fabricated by constructing a heterojunction of a semiconductor with a metal or a metal-like material. In the case of 2D material-based photodetectors, either the semiconductor or the metal belongs to the 2D family. The detection properties of Schottky contacted devices are mainly dependent on the junction properties such as the barrier height. The photodetection performance of detectors with 2D materials is observed to be superior and further it can be enhanced by tuning the properties through various strategies. Herein, the basic concepts, detection mechanism and evaluation parameters of Schottky junction-based photodetectors and the recent developments in Schottky junction-based photodetectors achieved using various 2D materials in the past five years are reviewed. Emerging strategies to enhance the performance by adjusting the Schottky barrier height are elaborated. Finally, the summary and future prospects are provided.

Ammonia gas sensing properties and density functional theory investigation of coral-like Au-SnSe2 Schottky junction

Abstract: This paper introduces a coral-like Au-modified SnSe2 nanocomposite prepared by a simple hydrothermal method. The pure- and Au-modified SnSe2 film sensors were prepared on the substrate with interdigitated electrodes by drop coating. The compositions, morphologies and microstructures of the as-synthesized nanomaterials were observed using transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The Au-modified SnSe2 nanocomposite has a coral-like morphology assembled from many irregular and very thin nanosheets. The gas performances of the film sensors at room temperature were tested through a series of experiments. The experimental results demonstrated that the Au-modified SnSe2 nanocomposite film sensor had excellent response characteristics, extremely short response/recovery time, outstanding gas selectivity and stability towards ammonia gas compared with the pure one. In addition, the first-principle density functional theory (DFT) was employed to simulate the effect of Au modification on gas adsorption behavior, clarifying the internal mechanism of gas sensing by combining with Au-SnSe2 Schottky junction. These results verified that the Au-modified SnSe2 film sensor is a high-performance candidate for enhanced ammonia gas sensing properties at room temperature.

A Bulk-Heterostructure Nanocomposite Electrolyte of Ce0.8Sm0.2O2-δ–SrTiO3 for Low-Temperature Solid Oxide Fuel Cells

Abstract: Since colossal ionic conductivity was detected in the planar heterostructures consisting of fluorite and perovskite, heterostructures have drawn great research interest as potential electrolytes for solid oxide fuel cells (SOFCs). However, so far, the practical uses of such promising material have failed to materialize in SOFCs due to the short circuit risk caused by SrTiO3. In this study, a series of fluorite/perovskite heterostructures made of Sm-doped CeO2 and SrTiO3 (SDC–STO) are developed in a new bulk-heterostructure form and evaluated as electrolytes. The prepared cells exhibit a peak power density of 892 mW cm−2 along with open circuit voltage of 1.1 V at 550 °C for the optimal composition of 4SDC–6STO. Further electrical studies reveal a high ionic conductivity of 0.05–0.14 S cm−1 at 450–550 °C, which shows remarkable enhancement compared to that of simplex SDC. Via AC impedance analysis, it has been shown that the small grain-boundary and electrode polarization resistances play the major roles in resulting in the superior performance. Furthermore, a Schottky junction effect is proposed by considering the work functions and electronic affinities to interpret the avoidance of short circuit in the SDC–STO cell. Our findings thus indicate a new insight to design electrolytes for low-temperature SOFCs.

Low-Voltage and Fast-Response SnO 2 Nanotubes/Perovskite Heterostructure Photodetector.

Abstract: One-dimensional metal-oxides (1D-MO) nanostructure has been regarded as one of the most promising candidates for high-performance photodetectors due to their outstanding electronic properties, low-cost and environmental stability However, the current bottlenecks are high energy consumption and relatively low sensitivity Here, Schottky junctions between nanotubes (NTs) and FTO were fabricated by electrospinning SnO2NTs on FTO glass substrate, and the bias voltage of SnO2NTs photodetectors was as low as ∼176 V, which can effectively reduce energy consumption Additionally, for improving the response and recovery speed of SnO2NTs photodetectors, the NTs were covered with organic/inorganic hybrid perovskite SnO2NTs/perovskite heterostructure photodetectors exhibit fast response/recovery speed (∼0075/004 s), and a wide optical response range (∼220-800 nm) At the same time, the bias voltage of heterostructure photodetectors was further reduced to 042 V The outstanding performance is mainly attributed to the formation of type-II heterojunctions between SnO2NTs and perovskite, which can facilitate the separation of photogenerated carriers, as well as Schottky junction between SnO2NTs and FTO, which reduce the bias voltage All the results indicate that the rational design of 1D-MO/perovskite heterostructure is a facile and efficient way to achieve high-performance photodetectors

Performance optimization of thermionic refrigerators based on van der Waals heterostructures

Abstract: In this paper, an irreversible thermionic refrigerator model based on van der Waals heterostructure with various irreversibilities is established by utilizing combination of non-equilibrium thermodynamics and finite time thermodynamics. The basic performance characteristics of the refrigerator are obtained. The effects of key factors, such as bias voltages, Schottky barrier heights and heat leakages, on the performance are studied. Results show that cooling rates and coefficients of performances (COPs) can attain the double maximum with proper modulation of barrier heights and bias voltages. Increasing cross-plane thermal resistance as well as decreasing electrode-reservoir thermal resistance and reservoir-reservoir thermal resistance can enhance the performance of the device. The optimal performance region is the interval between the maximum cooling rate point and the maximum COP point. By modulating the bias voltage, the working state of the device can fall into the optimal performance region. The optimal performance of the refrigerator when using single layer graphene and a few layers graphene as electrode material is also compared.

Interfacial Electronic Properties and Tunable Contact Types in Graphene/Janus MoGeSiN4 Heterostructures.

Abstract: Two-dimensional MoSi2N4 is an emerging class of 2D MA2N4 family, which has recently been synthesized in experiment. Herein, we construct ultrathin van der Waals heterostructures between graphene and a new 2D Janus MoGeSiN4 material and investigate their interfacial electronic properties and tunable Schottky barriers and contact types using first-principles calculations. The GR/MoGeSiN4 vdWHs are expected to be energetically favorable and stable. The high carrier mobility in graphene/MoGeSiN4 vdWHs makes them suitable for high-speed nanoelectronic devices. Furthermore, depending on the stacking patterns, either an n-type or a p-type Schottky contact is formed at the GR/MoGeSiN4 interface. The strain engineering and electric field can lead to the transformation from an n-type to a p-type Schottky contact or from Schottky to Ohmic contact in graphene/MoGeSiN4 heterostructure. These findings provide useful guidance for designing controllable Schottky nanodevices based on graphene/MoGeSiN4 heterostructures with high-performance.