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Maximizing the Current Output in Self-Aligned Graphene–InAs–Metal Vertical Transistors
摘要： With finite density of states and electrostatically tunable work function, graphene can function as a tunable contact for semiconductor channel to enable vertical field effect transistors (VFET). However, the overall performance, especially the output current density is still limited by the low conductance of the vertical semiconductor channel, as well as large series resistance of graphene electrode. To overcome these limitations, we construct a VFET by using single crystal InAs film as the high conductance vertical channel and self-aligned metal contact as the source-drain electrodes, resulting a record high current density over 45,000 A/cm2 at a low bias voltage of 1 V. Furthermore, we construct a device-level VFET model using resistor network method, and experimentally validate the impact of each geometry parameter on device performance. Importantly, we found the device performance is not only a function of intrinsic channel material, but also greatly influenced by device geometries and footprint. Our study not only pushes the performance limit of graphene VFETs, but also sheds light on van der Waals integration between two-dimensional material and conventional bulk material for high performance VFETs and circuits.
关键词： resistor network model,high current density,vertical transistor,graphene,van der Waals heterostructure,InAs film
更新于2025-09-23 15:23:52
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Near-direct bandgap WSe <sub/>2</sub> /ReS <sub/>2</sub> type-II pn heterojunction for enhanced ultrafast photodetection and high-performance photovoltaics
摘要： PN heterojunctions comprising layered van der Waals (vdW) semiconductors have been used to demonstrate current-rectifiers, photodetectors, and photovoltaic devices. However, a direct or near-direct heterointerface bandgap for enhanced photogeneration in high light-absorbing few-layer vdW materials remains unexplored. In this work, for the first time, density functional theory calculations show that the heterointerface of few-layer group-6 transition metal dichalcogenide (TMD) WSe2 with group-7 ReS2 results in a sizeable (0.7 eV) near-direct type-II bandgap. The interlayer IR bandgap is confirmed through IR photodetection and micro-photoluminescence measurements demonstrate type-II alignment. Few-layer flakes exhibit ultrafast response time (5 μs) and high responsivity (3 A/W) and large photocurrent-generation and responsivity-enhancement at the hetero-overlap region (10-100×). Large open-circuit voltage of 0.64 V and short-circuit current of 2.6 μA enable high output electrical power. Finally, long term air-stability and facile single contact metal fabrication process make the multi-functional few-layer WSe2/ReS2 heterostructure diode technologically promising for next-generation optoelectronics.
关键词： van der Waals heterostructure,pn heterojunction,ultrafast photodetection,near-direct bandgap,infrared photodetection,interlayer bandgap
更新于2025-09-23 15:19:57
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A Mixed-Dimensional van der Waals Heterostructure Photodetector
摘要： Van der Waals (vdW) heterostructures, integrated two-dimensional (2D) materials with variously functional materials, provide a distinctive platform for next-generation optoelectronics with unique flexibility and high performance. However, exploring the vdW heterostructures combined with strongly correlated electronic materials is hitherto rare. Herein, a novel temperature-sensitive photodetector based on the GaSe/VO2 mixed-dimensional vdW heterostructure is discovered. Compared with previous devices, our photodetector exhibits excellently enhanced performance, with external quantum efficiency up to 109.6 % and the highest responsivity (358.1 mA?W?1) under a 405 nm laser. Interestingly, we show that the heterostructure overcomes the limitation of a single material under the interaction between VO2 with GaSe, where photoresponse is highly sensitive to temperature and can be further shut at the critical value. The metal-insulator transition of VO2, which controls the peculiar band-structure evolution across the heterointerface, is demonstrated to manipulate the photoresponse variation. This study enables us to elucidate the method of manipulating 2D materials by strongly correlated electronic materials, paving the way for developing the high-performance and special optoelectronic application.
关键词： gallinum selenide,Vanadium dioxide,MIT-controlled photoresponse,mixed-dimensional van der Waals heterostructure,band engineering
更新于2025-09-23 15:19:57
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Tuning the electronic properties of van der Waals heterostructures composed of black phosphorus and graphitic SiC
摘要： This study presents a new van der Waals (vdW) heterostructure composed of monolayer black phosphorus (BP) and monolayer graphitic SiC (g-SiC). Using first-principles calculations, the structural and electronic properties of the BP/SiC heterostructure were investigated. It was found that by stacking BP with SiC, weak type-I band alignment can be achieved with a band gap of 0.705 eV, where the direct band gap as well as linear dichroism features were well preserved. The electrostatic potential drop in the heterojunction was calculated to be 4.044 eV. By applying perpendicular electric field, the band alignment can be altered to either type-I or type-II, and the band gap can be effectively controlled by field intensity, hence making the heterostructure suitable for various applications.
关键词： first-principles calculations,van der Waals heterostructure,graphitic SiC,electronic properties,black phosphorus
更新于2025-09-19 17:15:36
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The photovoltaic and photoconductive photodetector based on GeSe/2D semiconductor van der Waals heterostructure
摘要： Although plenty of two-dimensional (2D) semiconductor heterostructure photodetectors have been studied, there is still a lack of systematic comparison and analysis about photovoltaic and photoconductive 2D semiconductor photodetectors. Taking advantage of the 2D semiconductor van der Waals heterostructure, this work constructs a photovoltaic (PV) GeSe/MoS2 and a photoconductive (PC) GeSe/graphene photodetector, respectively. The PC GeSe/graphene photodetector achieves relatively higher photoresponsivity (R), where R can reach up to 104 AW(cid:2)1. The PV GeSe/MoS2 photodetector, by contrast, obtains a faster photoresponse speed. More importantly, the photoresponse properties of the PV GeSe/MoS2 photodetector can remain constant under the reverse bias, due to the minority carrier conduction in its depletion region at this time. The different characteristics of the two type 2D photodetectors are explored in detail, which can play a guiding role in the construction of high-performance photodetectors.
关键词： photovoltaic,photodetector,photoconductive,van der Waals heterostructure,2D semiconductor,GeSe
更新于2025-09-19 17:13:59
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Visible to Near-Infrared Photodetector Based on Graphene-MoTe2-Graphere Heterostructure
摘要： Graphene and transition metal dichalcogenides (TMDs) are widely investigated two dimensional materials in recent years. As a member of the TMDs family, MoTe2 possesses a suitable bandgap of ~1.0 eV for near infrared (NIR) photodetection. Here we stacked the MoTe2 flake with two graphene flakes of high carrier mobility to form a graphene-MoTe2-graphene heterostructure. It exhibits high photo-response to a broad spectrum range from 500 nm to 1300 nm. The photoresponsivity was calculated to be 1.6 A/W for the 750 nm light under 2 V/0 V drain-source/gate bias, and 154 mA/W for the 1100 nm light under 0.5 V/60 V drain-source/gate bias. Besides, the polarity of the photocurrent under zero Vds can be efficiently tuned by the back gate voltage to satisfy different applications. Finally, we fabricated a vertical graphene-MoTe2-graphene heterostructure photodetector which showed improved photoresponsivity of 3.3 A/W toward visible light.
关键词： photodetector,graphene,TMDs,van der Waals heterostructure,two-dimensional materials
更新于2025-09-19 17:13:59
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Self-Powered SnS1-xSex Alloy/Silicon Heterojunction Photodetectors with High Sensitivity in a Wide Spectral Range
摘要： Alloy engineering and heterostructures designing are two efficient methods to improve the photosensitivity of 2D material-based photodetectors. Herein, we report the first-principle calculation about the band structure of SnS1-xSex (0 ≤ x ≤ 1) and synthesize these alloy nanosheets. Systematic measurements indicate that SnS0.25Se0.75 exhibits the highest hole mobility (0.77 cm2·V-1·s-1) and a moderate photoresponsivity (4.44 × 102 A·W-1) with fast response speed (32.1/57.5 ms) under 635 nm irradiation. Furthermore, to reduce the dark current and strengthen the light absorption, a self-driven SnS0.25Se0.75/n-Si device has been fabricated. The device achieved a preeminent photo-responsivity of 377 mA·W-1, a detectivity of ~1011 Jones and Ilight/Idark ratio of ~4.5×102. In addition, the corresponding rising/decay times are as short as 4.7/3.9 ms. Moreover, a broadband sensitivity from 635 nm to 1200 nm is obtained and the related photoswitching curves are stable and reproducibility. Noticeably, the above parameters are comparable or superior to the most of reported group IVA layered materials-based self-driven photodetectors. Last, the synergistic effects between the SnS0.25Se0.75 nanosheets and the n-Si have been discussed by the band alignment. These brilliant results will pave a new pathway for the development of next generation 2D alloy-based photoelectronic devices.
关键词： alloy engineering,photodetectors,Tin chalcogenides,physical vapor deposition,van der Waals heterostructure
更新于2025-09-16 10:30:52
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High Performance Van der Waals Graphene–WS <sub/>2</sub> –Si Heterostructure Photodetector
摘要： 2D materials have become a major focus in material science due to their exotic properties originated from quantum confinement effects. Van der Waals heterostructures composed of 2D materials and conventional semiconductors always show enhanced optoelectronic performance and have attracted much attention in recent years. Here, high performance photodetectors based on graphene–WS2–Si van der Waals heterostructure is reported. The photodetector shows wide spectrum response from visible to near infrared with a maximum photoresponsivity of 54.5 A W?1 at 800 nm. Furthermore, the photodetector has a fast response speed with rise time of 45 μs and decay time of 210 μs. Photocurrent mapping shows that not only the graphene–WS2–Si area, but also the graphene–WS2–SiO2–Si area contributes to the photocurrent. With the increase of lateral size of the junction area, the photoresponsivity is reduced due to increased recombination. The response speed decreases with the increase of lateral size of the junction area, which is due to increased junction capacitance. The results indicate that this kind of van der Waals heterostructure has excellent photodetection performance and is suitable for application in high performance broadband photodetectors. Also, the simple fabrication method has a great potential for large scale device integration.
关键词： van der Waals heterostructure,photodetector,WS2,graphene,Si
更新于2025-09-12 10:27:22
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Electric field mediated large valley splitting in the van der Waals heterostructure WSe <sub/>2</sub> /CrI <sub/>3</sub>
摘要： In contrast to commonly used means such as the magnetic field, here an electric field is used to achieve a large valley splitting in the van der Waals (vdW) heterostructure WSe2/CrI3. CrI3 contributes to the spin moment. The electric field pushes the valence bands of Cr atoms close to those of the W atoms associated with pseudospin so that they can interact through the exchange interaction. The opposite helicities of pseudospin at the K and K′ points realize a valley splitting as large as 10.5 meV under an electric field of 0.1 V ??1. The underlying physics stems from the interlayer charge transfer, where the spin conservation plays a role.
关键词： van der Waals heterostructure,WSe2/CrI3,electric field,pseudospin,valley splitting
更新于2025-09-04 15:30:14
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Prediction of Adsorption Probability of Oxidizing and Reducing Species on 2D Hybrid Junction of rGO-ZnO from First Principle Analysis
摘要： The target of this paper is to theoretically investigate the probability of gas (both oxidizing and reducing) adsorption on the van der Waals (vdW) heterojunction formed between p-type rGO and n-type 2D-ZnO, using density functional theory (DFT) based first principle calculation employing Virtual Nanolab (VNL) Atomistix Toolkit (ATK) (v2016.4). Two types of heterostructures are considered viz. heterostructure type-1 where hydroxyl group (sp2) is at the edge of the reduced graphene oxide (rGO) and heterostructure type-2 where hydroxyl group (sp3) is perpendicular to the plane of rGO. Adsorption energy, charge transfer and the distance of the nearest atom from the adsorbent are calculated for oxidizing (NO2 as the test case) and reducing (NH3 as the test case) species and compared with that of Oxygen on rGO/2D-ZnO heterostructures as well as on its individual constituent (rGO nanoflakes and 2D-ZnO, separately). Like 2D-ZnO, heterostructure type-1 was also found to be selective towards NO2 with almost three times and five times higher adsorption energy than that of 2D-ZnO and rGO, respectively. On the other hand, it was found that charge distribution in the underlying 2D-ZnO of heterostructure type-2 remained almost unaltered even after gas adsorption and therefore lead to insignificant improvement compared to its 2D-ZnO counterpart.
关键词： gas adsorption probability,charge transfer,van der Waals heterostructure,Density functional theory,rGO-ZnO hybrid system
更新于2025-09-04 15:30:14