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Assembling two-dimensional (2D) crystals via weak van der Waals (vdW) interactions in a vertical stack reveals various exciting physical phenomena and becomes essential for high-performance electronic devices through band alignment modulation. These vdW heterostructures enable the creation of primary electronic components, such as diodes and transistors, facilitating multifunctional device integration on a single chip and offering significant potential for analog and digital electronics. This study demonstrates the potential of metal–insulator–semiconductor (MIS) diodes within 2D vdW heterostructures, focusing on a combination of black phosphorus (BP), thin hexagonal boron nitride (hBN), and graphene (Gr). The BP/hBN/Gr MIS diode is fabricated using a dry transfer method to vertically stack the layered materials. Comparative analysis with similar metal–semiconductor diodes reveals superior current rectification in the MIS diode, attributed to carrier tunneling at the interfaces. We evaluate the performance metrics, including the rectification ratio, ideality factor, and tunneling behavior, over a temperature range of 77–300 K. The device exhibits a rectification ratio of 3.5 × 102 and an ideality factor of 1.6. Our findings highlight the potential of MIS diodes in ultrathin nanoelectronics, offering insights for future advancements in electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

The exponential development in quantum phenomena is directly correlated with the decreasing size of nano‐semiconductor transistors. Consequently, the use of a quantum structure that deviates from traditional transistor types becomes imperative. Electrostatically defined nanoscale devices within 2D semiconductor heterostructures serve as foundational elements for diverse quantum electrical circuits. Van der Waals heterostructures, distinguished by atomically flat interfaces and inherent 2D characteristics, offer advantages such as large‐scale uniformity, flexibility, and portability over conventional bulk semiconductor heterostructures. Herein, the intricate electronic behavior of a MoS2/WSe2 encapsulated heterostructure governed by split‐gate and middle‐gate configurations is investigated, revealing a distinctive step‐like current profile at a low temperature of 77 K. The observed four regimes in the current highlight the impact of quantum confinement induced by reduced lateral dimensions, coupled with precise electrostatic confinement controlled by gate voltages. The temperature dependence of the phenomena emphasizes the role of thermal effects on carrier scattering mechanisms. In addition, the pinch‐off characteristics with different temperatures, middle‐gate voltages, and drain biases are explored. This study contributes to a deeper understanding of electrostatic effects in 2D transition metal dichalcogenide heterostructures and holds promise for the development of advanced electronic devices with tailored confinement for enhanced functionalities. [ABSTRACT FROM AUTHOR]

A two-dimensional (2D) atomic crystalline transition metal dichalcogenides has shown immense features, aiming for future nanoelectronic devices comparable to conventional silicon (Si). 2D molybdenum ditelluride (MoTe2) has a small bandgap, appears close to that of Si, and is more favorable than other typical 2D semiconductors. In this study, we demonstrate laser-induced p-type doping in a selective region of n-type semiconducting MoTe2 field effect transistors (FET) with an advance in using the hexagonal boron nitride as passivation layer from protecting the structure phase change from laser doping. A single nanoflake MoTe2-based FET, exhibiting initial n-type and converting to p-type in clear four-step doping, changing charge transport behavior in a selective surface region by laser doping. The device shows high electron mobility of about 23.4 cm2V−1s−1 in an intrinsic n-type channel and hole mobility of about 0.61 cm2V−1s−1 with a high on/off ratio. The device was measured in the range of temperature 77–300 K to observe the consistency of the MoTe2-based FET in intrinsic and laser-dopped region. In addition, we measured the device as a complementary metal–oxide–semiconductor (CMOS) inverter by switching the charge-carrier polarity of the MoTe2 FET. This fabrication process of selective laser doping can potentially be used for larger-scale MoTe2 CMOS circuit applications. [ABSTRACT FROM AUTHOR]

Stacking of graphene with hexagonal boron nitride (h-BN) can dramatically modify its bands from their usual linear form, opening a series of narrow minigaps that are separated by wider minibands. While the resulting spectrum offers strong potential for use in functional (opto)electronic devices, a proper understanding of the dynamics of hot carriers in these bands is a prerequisite for such applications. In this work, we therefore apply a strategy of rapid electrical pulsing to drive carriers in graphene/h-BN heterostructures deep into the dissipative limit of strong electron-phonon coupling. By using electrical gating to move the chemical potential through the "Moiré bands", we demonstrate a cyclical evolution between metallic and semiconducting states. This behavior is captured in a self-consistent model of non-equilibrium transport that considers the competition of electrically driven inter-band tunneling and hot-carrier scattering by strongly non-equilibrium phonons. Overall, our results demonstrate how a treatment of the dynamics of both hot carriers and hot phonons is essential to understanding the properties of functional graphene superlattices. Significant attention has been devoted to understanding the low-electric-field properties of carriers in moiré graphene, but high-electric-field transport has not been as well explored. Here, the authors find non-monotonic transport behavior at moiré minigaps due to competition between inter-band tunneling and coupling to out-of-equilibrium phonons. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) atomic crystalline materials have attracted the scientific community owing to their remarkable electrical and optical applications, such as solar cells, light-emitting diodes, and photodiodes. This study demonstrates a Schottky barrier photodiode (SPD) using different metal architectures in lateral and vertical contacts on n-type 2H phase semiconducting molybdenum ditelluride (MoTe2) synthesized by the self-flux crystal growth method. High-work-function palladium and low-work-function indium metals have been deposited on MoTe2 to fabricate a field-effect transistor confirming diode characteristics. The device shows an ideality factor of 1.09 and a rectification ratio of 102, indicating ideal diode characteristics based on a single MoTe2 channel. In addition, we measured the device in the dark and used the green laser to analyze the photodiode behavior of SPD in a wide range of light intensity. A single channel using contact architecture-based study is helpful to apply in other 2D materials to achieve the simplest fundamental diodes for future nanoelectrical and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Diode characteristics of transition metal dichalcogenides are studied extensively owing to their electrical and optical properties. In particular, the Schottky barrier diode (SBD) structure has advantages, such as its small leakage current and power consumption, over conventional p–n diodes. This study develops an SBD system using n‐type tungsten disulfide (WS2). By depositing a low work function In (ΦIn = 4.1 eV) and high work function Au (ΦAu = 5.1 eV) on n‐type WS2, the diode characteristics are demonstrated to be close to an ideal diode. The In–Au contacts are measured, and SBD characteristics are confirmed with a 1.02 ideality factor at a zero back‐gate voltage at room temperature and a rectification ratio up to 5 × 102, even at a low temperature (77 K), indicating almost ideal diode properties. In addition, the In electrodes exhibited improved electrical properties, with a high on/off ratio of 107, mobility that is 100 times higher, and Schottky barrier height that is 20 times lower than that of Au electrodes. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) molybdenum disulphide (MoS2) transition metal dichalcogenides (TMDs) have great potential for use in optical and electronic device applications; however, the performance of MoS2 is limited by its crystal quality, which serves as a measure of the defects and grain boundaries in the grown material. Therefore, the high-quality growth of MoS2 crystals continues to be a critical issue. In this context, we propose the formation of high-quality MoS2 crystals via the flux method. The resulting electrical properties demonstrate the significant impact of crystal morphology on the performance of MoS2 field-effect transistors. MoS2 made with a relatively higher concentration of sulphur (a molar ratio of 2.2) and at a cooling rate of 2.5 °C h−1 yielded good quality and optimally sized crystals. The room-temperature and low-temperature (77 K) electrical transport properties of MoS2 field-effect transistors (FETs) were studied in detail, with and without the use of a hexagonal boron nitride (h-BN) dielectric to address the mobility degradation issue due to scattering at the SiO2/2D material interface. A maximum field-effect mobility of 113 cm2 V−1 s−1 was achieved at 77 K for the MoS2/h-BN FET following high-quality crystal formation by the flux method. Our results confirm the achievement of large-scale high-quality crystal growth with reduced defect density using the flux method and are key to achieving higher mobility in MoS2 FET devices in parallel with commercially accessible MoS2 crystals. [ABSTRACT FROM AUTHOR]

In this study, we fabricated quantum point contacts narrower than 100 nm by using an electrostatic potential to open the finite bandgap by applying a perpendicular electric field to bilayer graphene encapsulated between hexagonal boron nitride sheets. The conductance across the quantum point contact was quantized at a high perpendicular-displacement field as high as 1 V/nm at low temperature, and the quantization unit was 2e2/h instead of mixed spin and valley degeneracy of 4e2/h. This lifted degeneracy state in the quantum point contact indicates the presence of valley polarized state coming from potential profile or effective displacement field in one-dimensional channel. [ABSTRACT FROM AUTHOR]

Manipulation of Ohmic contacts in 2D transition metal dichalcogenides for enhancing the transport properties and enabling its application as a practical device has been a long‐sought goal. In this study, n‐type tungsten disulfide (WS2) single atomic layer to improve the Ohmic contacts of the p‐type molybdenum ditelluride (MoTe2) material is covered. The Ohmic properties, based on the lowering of Schottky barrier height (SBH) owing to the tunneling barrier effect of the WS2 monolayer, are found to be unexpectedly excellent at room temperature and even at 100 K. The improved SBH and contact resistances are 3 meV and 1 MΩ µm, respectively. The reduction in SBH and contact resistance is confirmed with temperature‐dependent transport measurements. This study further demonstrates the selective carrier transport across the MoTe2 and WS2 layers by modulating the applied gate voltage. This WS2/MoTe2 heterostructure exhibits excellent gate control over the currents of both channels (n‐type and p‐type). The on/off ratios for both the electron and hole channels are calculated as 107 and 106, respectively, indicating good carrier type modulation by the electric field of the gate electrode. The Ohmic contact resistance using the tunneling of the atomic layer can be applied to heterojunction combinations of various materials. [ABSTRACT FROM AUTHOR]

The integration of electrical contact into 2D heterostructure is an essential approach to high-quality electronic nano-devices, especially field-effect transistors. However, high contact resistance with transition metal dichalcogenides such as molybdenum disulphide (MoS2)-based devices has been a significant fabrication impediment to their potential applications. Here, we have demonstrated the advantage of 1D indium metal contact with fully encapsulated MoS2 within hexagonal boron nitride. The electrical measurements of the device exhibit ambipolar transport with an on/off ratio of for holes and for electrons. The device exhibits high field-effect mobility of at liquid nitrogen temperature. Furthermore, we have also analysed the charge-transport mechanism at the interface and have calculated the Schottky barrier height from the temperature-dependent measurement. These results are highly promising for the use of air-sensitive material heterostructure and large-scale design of trending flexible, transparent electronic wearable devices. [ABSTRACT FROM AUTHOR]

Single crystalline Ni nanowires (with a controlled diameter of ∼14 nm) have been fabricated by electrochemical deposition in etched ion-track polycarbonate templates. The exchange bias effect in these nanowires has been studied at 10 K under a cooling field of 10 kOe applied parallel to the wire axis for different time intervals starting from the as-fabricated to ∼2 yr old samples. A continuous drop in the saturation magnetization has been observed with time due the formation of an antiferromagnetic oxide layer at the periphery of nanowires. A model for the drop of magnetization has been used to calculate the thickness of the oxide layer in nickel nanowires. The observed variation in exchange bias and saturation magnetization has been explained by taking into account the exchange interactions at the Ni-NiO interface and the development of antiferromagnetic NiO at the expense of metallic Ni. [ABSTRACT FROM AUTHOR]

This paper investigates how postgrowth annealing affects the structure and the electro-optical properties of low-temperature grown GaAs (LT-GaAs). A systematic study of as-grown and annealed LT-GaAs revealed that the carrier lifetime is directly related to the density of the An duster and distance between As clusters. The Ga/As compositional ratio and the crystal structure of As clusters were observed for the first time. The As/Ga ratio of the As clusters is higher than that obtained from the LT-GaAs. The carrier lifetime of the annealed LT-GaAs increases as the annealing temperature increases from 400 (less than 30 fs) to 800 °C (824 fs). Under the annealing temperatures ranging from 600 to 700 °C for 90 s, we observed the emission of terahertz radiation using the annealed LT-GaAs grown at temperatures ranging from 260 to 320 °C. [ABSTRACT FROM AUTHOR]

We report the drastic enhancement pattern of Shubnikov-de Haas (SdH) oscillations observed in an AlGaN/GaN heterostructure by microwave modulation. The dependence of the SdH pattern on microwave power and temperature is investigated. The underlying mechanism is attributed to the effect of carrier heating. This technique helps study the transport properties of two-dimensional electrons in many wide-band-gap heterostructures, in which moderate mobilities and heavier electron effective mass (rapidly damping SdH amplitudes) are frequently encountered. In addition, this method has the advantage of keeping the carrier concentration fixed and not requiring expensive high-energy laser facilities compared with carrier-modulated SdH measurements. [ABSTRACT FROM AUTHOR]

Unintentionally formed nanocrystalline graphene (nc-G) can act as a useful seed for the large-area synthesis of a hexagonal boron nitride (h-BN) thin film with an atomically flat surface that is comparable to that of exfoliated singlecrystal h-BN. A wafer-scale dielectric h-BN thin film was successfully synthesized on a bare sapphire substrate by assistance of nc-G, which prevented structural deformations in a chemical vapor deposition process. The growth mechanism of this nc-G-tailored h-BN thin film was systematically analyzed. This approach provides a novel method for preparing high-quality two-dimensional materials on a large surface. [ABSTRACT FROM AUTHOR]

Unintentionally formed nanocrystalline graphene (nc-G) can act as a useful seed for the large-area synthesis of a hexagonal boron nitride (h-BN) thin film with an atomically flat surface that is comparable to that of exfoliated singlecrystal h-BN. A wafer-scale dielectric h-BN thin film was successfully synthesized on a bare sapphire substrate by assistance of nc-G, which prevented structural deformations in a chemical vapor deposition process. The growth mechanism of this nc-G-tailored h-BN thin film was systematically analyzed. This approach provides a novel method for preparing high-quality two-dimensional materials on a large surface. [ABSTRACT FROM AUTHOR]

Rapid thermal annealing of VO2 nanobeams in an ambient argon environment has been carried out at various temperatures after device fabrication. Our analysis revealed that increasing the annealing temperature from 200 °C to 400 °C results in the reduction of both ohmic and nanobeam resistances with an appreciable decrease in joule-heating based transition voltage and transition temperature, while samples annealed at 500 °C exhibited a conducting rutile-phase like characteristics at room temperature. In addition, these variation trends were explored using a physical model and the results were found to be in agreement with the observed results, thus verifying the model. [ABSTRACT FROM AUTHOR]

Chemo-resistive hydrogen-gas sensors based on thermally reduced graphene oxide (rGO) have been fabricated on a micro-hotplate by positive ac dielectrophoresis (DEP). The optimized DEP parameters for manipulating rGO nanostructures into Au electrodes for hydrogen sensing are: applied frequency = 1 MHz, peak-to-peak voltage = 5 V, and DEP time = 30 s. The device exhibits good sensitivity (∼6%) with fast response time (∼11 s) and recovery time (∼36 s) for 200 ppm hydrogen gas at room temperature. This result indicates that the DEP process has great potential for assembling rGO for hydrogen-gas sensor in many industrial and scientific applications. [ABSTRACT FROM AUTHOR]

Short range interaction between two dimensional electron gas (2DEG) and InAs quantum dots embedded in the GaAs/AlGaAs quantum well is investigated as a function of carrier density. At low carrier density the interaction is significantly characterized by a transport to quantum lifetime ratio of less than 5. However, with an increase in carrier density, quantum lifetime is observed to undergo a sharp transition from 0.17 to 0.25 ps. This is attributed to the screening of short range repulsive scattering due to InAs quantum dots by the 2DEG. [ABSTRACT FROM AUTHOR]

Electron and hole sublevels in quantum dots (QDs) are experimentally determined using the excitation-power dependence of photoluminescence spectrum for a modulation-doped QD structure. The sublevel spacing between n=1 and n=2 electron states can be obtained from the photoluminescence (PL) spectrum under very low excitation and the spacing between n=1 and n=2 hole states can be obtained by comparing the PL spectrum under high excitation with the one under low excitation. The proposed method should give useful information in the design of QD devices, as well as for the verification of theoretical calculations of QD energy levels. [ABSTRACT FROM AUTHOR]

Highly conductive and water-dispersible sheets of reduced graphene oxide (RGO) were produced by rapidly heating graphene oxide (GO) paper at a low temperature (300 °C) for a short processing time of 3 s. The GO paper was thermally treated during the rapid-heating reduction process and, consequently, the oxygen functional groups in the obtained RGO were highly reduced. The RGO film displays good thermal stability, crystallinity, low sheet resistance, and good dispersibility in water, which makes it an ideal candidate to be used in various carbon-based electronic devices. We finally demonstrate the suitability of RGO as an active channel material and as a source-drain electrode for graphene field-effect transistors, which bring the possibility of realizing all-carbon devices a step closer to reality. [ABSTRACT FROM AUTHOR]

We present a study of the anisotropic properties of two-dimensional electron gases formed in GaAs/AlGaAs heterostructures in which InAs self-assembled quantum dots have been inserted into the center of a GaAs quantum well. We observe an anisotropic mobility for the orthogonal [1¯10] and [110] directions. The mobility in the [1¯10] direction was found to be up to approximately twice that in the [110] direction. It is suggested that the interface roughness scattering due to the inserted InAs material could be a cause for the large anisotropies in mobility. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We studied insulator–metal transitions in VO2 nanobeams for both abrupt and gradual changes in applied electric fields. Based on the observations, the Poole–Frenkel effect explained the abrupt transition, while the gradual case is found to be dominated by the Joule heating phenomenon. We also carried out power model and finite element method based simulations which supported the Joule heating phenomena for gradual transition. An in-principle demonstration of the Poole–Frenkel effect, performed using a square voltage pulse of 1 µs duration, further confirms the proposed insulator–metal transition mechanism with a switching time in the order of 100 ns. Finally, conductivity variations introduced via rapid thermal annealing at various temperatures validate the roles of both Joule heating and Poole–Frenkel mechanisms in the transitions. [ABSTRACT FROM AUTHOR]

We describe a detailed device fabrication technique for the formation of a lateral quantum dot using a multilayered gated design. In our versatile system, a quantum dot is electrostatically defined by a split gate and two overlaying finger gates which introduce entrance and exit barriers to the dot. Periodic and continuous conductance oscillations arising from Coulomb charging effects are clearly observed in the transport properties at low temperatures. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]