Explore the vast range of titles available.

A main challenge for the development of two‐dimensional devices based on atomically thin transition‐metal dichalcogenides (TMDs) is the realization of metal–semiconductor junctions (MSJs) with low contact resistance and high charge transport capability. However, traditional metal–TMD junctions usually suffer from strong Fermi‐level pinning (FLP) and chemical disorder at the interfaces, resulting in weak device performance and high energy consumption. By means of high‐throughput first‐principles calculations, we report an attractive solution via the formation of van der Waals (vdW) contacts between metallic and semiconducting TMDs. We apply a phase‐engineering strategy to create a monolayer TMD database for achieving a wide range of work functions and band gaps, hence offering a large degree of freedom to construct TMD vdW MSJs with desired contact types. The Schottky barrier heights and contact types of 728 MSJs have been identified and they exhibit weak FLP (−0.62 to −0.90) as compared with the traditional metal–TMD junctions. We find that the interfacial interactions of the MSJs bring a delicate competition between the FLP strength and carrier tunneling efficiency, which can be utilized to screen high‐performance MSJs. Based on a set of screening criteria, four potential TMD vdW MSJs (e.g., NiTe2/ZrSe2, NiTe2/PdSe2, HfTe2/PdTe2, TaSe2/MoTe2) with Ohmic contact, weak FLP, and high carrier tunneling probability have been predicted. This work not only provides a fundamental understanding of contact properties of TMD vdW MSJs but also renders their huge potential for electronics and optoelectronics. An attractive strategy via the formation of van der Waals (vdW) contacts between atomically thin metallic and semiconducting transition‐metal dichalcogenides (TMDs) is proposed to suppress strong Fermi‐level pinning at the metal–semiconductor interfaces. By means of high‐throughput first‐principles calculations, a series of phase‐engineered TMD‐based vdW metal–semiconductor junctions with weak Fermi‐level pining and high carrier tunneling probability have been screened.

Tribovoltaic devices have emerged as promising technologies for converting mechanical motion to electricity via surface charge generation. To maximize the electromechanical conversion of tribovoltaic devices, conventional literature has focussed on engineering a large difference in work functions between the contact materials. However, recent reports suggest that other factors beyond work function, such as temperature, play a key role in electromechanical conversion. Herein, TiO2 (a cheap, abundant oxide material) is doped with Nb5+, resulting in an improved tribovoltaic performance up to 65 times. This is attributed to an enhancement in the TiO2 film conductivity arising from Nb5+ doping. Further, it is shown that this improvement holds over cm2 scale testing. This work demonstrates the importance of considering a range of factors, particularly conductivity, when designing tribovoltaic devices and may be adopted broadly for optimal electromechanical conversion. Here the role of electronic conductivity and doping in Tribovoltaic devices is studied on the cm2 scale, using cheap, abundant TiO2. TiO2 is doped with Nb5+ leading to a decrease in resistivity and increase in measured current (x65). The films show excellent stability over 1000 cycles, and the insights gained can be used for future design of optimal tribovoltaic devices.

The development of next-generation electronics requires scaling of channel material thickness down to the two-dimensional limit while maintaining ultralow contact resistance 1 , 2 . Transition-metal dichalcogenides can sustain transistor scaling to the end of roadmap, but despite a myriad of efforts, the device performance remains contact-limited 3 – 12 . In particular, the contact resistance has not surpassed that of covalently bonded metal–semiconductor junctions owing to the intrinsic van der Waals gap, and the best contact technologies are facing stability issues 3 , 7 . Here we push the electrical contact of monolayer molybdenum disulfide close to the quantum limit by hybridization of energy bands with semi-metallic antimony ( 01 1 ̅ 2 ) through strong van der Waals interactions. The contacts exhibit a low contact resistance of 42 ohm micrometres and excellent stability at 125 degrees Celsius. Owing to improved contacts, short-channel molybdenum disulfide transistors show current saturation under one-volt drain bias with an on-state current of 1.23 milliamperes per micrometre, an on/off ratio over 10 8 and an intrinsic delay of 74 femtoseconds. These performances outperformed equivalent silicon complementary metal–oxide–semiconductor technologies and satisfied the 2028 roadmap target. We further fabricate large-area device arrays and demonstrate low variability in contact resistance , threshold voltage, subthreshold swing, on/off ratio, on-state current and transconductance 13 . The excellent electrical performance, stability and variability make antimony ( 01 1 ̅ 2 ) a promising contact technology for transition-metal-dichalcogenide-based electronics beyond silicon. The electrical contact of two-dimensional transistors is pushed close to the quantum limit by hybridization of the energy bands with antimony; the contacts have low contact resistance and excellent stability.

Improving the performance of generation, transport and injection of hot carriers within metal/semiconductor junctions is critical for promoting the hot-carrier applications. However, the conversion efficiency of hot carriers in the commonly used noble metals (e.g., Au) is extremely low. Herein, through a systematic study by first-principles calculation and Monte Carlo simulation, we show that TiN might be a promising plasmonic material for high-efficiency hot-carrier applications. Compared with Au, TiN shows obvious advantages in the generation (high density of low-energy hot electrons) and transport (long lifetime and mean free path) of hot carriers. We further performed a device-oriented study, which reveals that high hot-carrier injection efficiency can be achieved in core/shell cylindrical TiN/TiO 2 junctions. Our findings provide a deep insight into the intrinsic processes of hot-carrier generation, transport and injection, which is helpful for the development of hot-carrier devices and applications.

Geometry-induced doping (G-doping) has been realized in semiconductors nanograting layers. G-doping-based p-p(v) junction has been fabricated and demonstrated with extremely low forward voltage and reduced reverse current. The formation mechanism of p-p(v) junction has been proposed. To obtain G-doping, the surfaces of p-type and p+-type silicon substrates were patterned with nanograting indents of depth d = 30 nm. The Ti/Ag contacts were deposited on top of G-doped layers to form metal-semiconductor junctions. The two-probe method has been used to record the I–V characteristics and the four-probe method has been deployed to exclude the contribution of metal-semiconductor interface. The collected data show a considerably lower reverse current in p-type substrates with nanograting pattern. In the case of p+-type substrate, nanograting reduced the reverse current dramatically (by 1–2 orders of magnitude). However, the forward currents are not affected in both substrates. We explained these unusual I–V characteristics with G-doping theory and p-p(v) junction formation mechanism. The decrease of reverse current is explained by the drop of carrier generation rate which resulted from reduced density of quantum states within the G-doped region. Analysis of energy-band diagrams suggested that the magnitude of reverse current reduction depends on the relationship between G-doping depth and depletion width.

HighlightsMo–MXene/Mo–metal sulfides with semiconductor junctions and Mott–Schottky junctions are designed.Built-in electric field are constructed in semiconductor–semiconductor–metal heterostructure, enhancing dielectric polarization and impedance matching.Density functional theory calculations and Radar cross-section simulations confirmed the excellent electromagnetic wave absorption ability of heterostructures.The exploration of novel multivariate heterostructures has emerged as a pivotal strategy for developing high-performance electromagnetic wave (EMW) absorption materials. However, the loss mechanism in traditional heterostructures is relatively simple, guided by empirical observations, and is not monotonous. In this work, we presented a novel semiconductor–semiconductor–metal heterostructure system, Mo–MXene/Mo–metal sulfides (metal = Sn, Fe, Mn, Co, Ni, Zn, and Cu), including semiconductor junctions and Mott–Schottky junctions. By skillfully combining these distinct functional components (Mo–MXene, MoS2, metal sulfides), we can engineer a multiple heterogeneous interface with superior absorption capabilities, broad effective absorption bandwidths, and ultrathin matching thickness. The successful establishment of semiconductor–semiconductor–metal heterostructures gives rise to a built-in electric field that intensifies electron transfer, as confirmed by density functional theory, which collaborates with multiple dielectric polarization mechanisms to substantially amplify EMW absorption. We detailed a successful synthesis of a series of Mo–MXene/Mo–metal sulfides featuring both semiconductor–semiconductor and semiconductor–metal interfaces. The achievements were most pronounced in Mo–MXene/Mo–Sn sulfide, which achieved remarkable reflection loss values of − 70.6 dB at a matching thickness of only 1.885 mm. Radar cross-section calculations indicate that these MXene/Mo–metal sulfides have tremendous potential in practical military stealth technology. This work marks a departure from conventional component design limitations and presents a novel pathway for the creation of advanced MXene-based composites with potent EMW absorption capabilities.

The junctions formed at the contact between metallic electrodes and semiconductor materials are crucial components of electronic and optoelectronic devices 1 . Metal–semiconductor junctions are characterized by an energy barrier known as the Schottky barrier, whose height can, in the ideal case, be predicted by the Schottky–Mott rule 2 – 4 on the basis of the relative alignment of energy levels. Such ideal physics has rarely been experimentally realized, however, because of the inevitable chemical disorder and Fermi-level pinning at typical metal–semiconductor interfaces 2 , 5 – 12 . Here we report the creation of van der Waals metal–semiconductor junctions in which atomically flat metal thin films are laminated onto two-dimensional semiconductors without direct chemical bonding, creating an interface that is essentially free from chemical disorder and Fermi-level pinning. The Schottky barrier height, which approaches the Schottky–Mott limit, is dictated by the work function of the metal and is thus highly tunable. By transferring metal films (silver or platinum) with a work function that matches the conduction band or valence band edges of molybdenum sulfide, we achieve transistors with a two-terminal electron mobility at room temperature of 260 centimetres squared per volt per second and a hole mobility of 175 centimetres squared per volt per second. Furthermore, by using asymmetric contact pairs with different work functions, we demonstrate a silver/molybdenum sulfide/platinum photodiode with an open-circuit voltage of 1.02 volts. Our study not only experimentally validates the fundamental limit of ideal metal–semiconductor junctions but also defines a highly efficient and damage-free strategy for metal integration that could be used in high-performance electronics and optoelectronics. In metal–semiconductor junctions, interfacial bonding and disorder cause deviations from theoretical predictions for the energy barrier, but delicately transferring pre-fabricated metal films onto two-dimensional semiconductors can overcome this challenge.

Gas sensor based on the Ultraviolet and Ozone (UVO) treated Chemical Vapor Deposition (CVD) Graphene Oxide (GO) and the Ion Sensitive GO-Si based metal-semiconductor junction resistor was designed and realized. Under different gate voltages, the response characteristics of the sensor to ammonia concentration, as well as the selectivity and stability of the sensor were studied. The test results show that the comprehensive performance of the gas sensor is the best when the UVO processing time is 1 min and the applied gate voltage is −9 V. The proposed Ion Sensitive GO-Si based metal-semiconductor junction resistor Gas Sensor can detect 250 ppb ammonia with a sensitivity of 4%. The detection limit of the sensor is 50 ppb. Using acetone and ethanol as contrast gases, the sensor shows better selectivity for ammonia. The sensitivity retention rate of the sensor after 10 days is higher than 70%, which indicates that the sensor has a good retention performance.

High Schottky barrier heights at metal–semiconductor junctions due to Fermi-level pinning can degrade the performance of electronic devices and increase their energy consumption. Van der Waals contacts between metals and two-dimensional semiconductors without Fermi-level pinning are theoretically possible, but have not been achieved due to the presence of interactions such as interface defects and orbital overlap. Here we show that interaction- and defect-free van der Waals contacts can be formed between a range of metals and two-dimensional semiconductors via a metal deposition process that uses a selenium buffer layer. Our contacts obey the Schottky–Mott rule and have a Fermi-level pinning of –0.91. A comparison between the van der Waals contacts and typical direct metal contacts reveals differences in interface gap distances, band bending and electrical characteristics. Using gold van der Waals contacts, we fabricate p-type tungsten diselenide field-effect transistors that exhibit stable operation with on/off ratio of 10 6 , mobility of 155 cm 2  (V s) –1 , contact resistance of 1.25 kΩ μm and Schottky barrier height of 60 meV. High-quality van der Waals contacts between metals and two-dimensional semiconductors can be created using a selenium buffer layer that is deposited before the metal deposition process.

Magnetic tunnel junctions (MTJs) with conventional bulk ferromagnets separated by a nonmagnetic insulating layer are key building blocks in spintronics for magnetic sensors and memory. A radically different approach of using atomically-thin van der Waals (vdW) materials in MTJs is expected to boost their figure of merit, the tunneling magnetoresistance (TMR), while relaxing the lattice-matching requirements from the epitaxial growth and supporting high-quality integration of dissimilar materials with atomically-sharp interfaces. We report TMR up to 192% at 10 K in all-vdW Fe 3 GeTe 2 /GaSe/Fe 3 GeTe 2 MTJs. Remarkably, instead of the usual insulating spacer, this large TMR is realized with a vdW semiconductor GaSe. Integration of semiconductors into the MTJs offers energy-band-tunability, bias dependence, magnetic proximity effects, and spin-dependent optical-selection rules. We demonstrate that not only the magnitude of the TMR is tuned by the semiconductor thickness but also the TMR sign can be reversed by varying the bias voltages, enabling modulation of highly spin-polarized carriers in vdW semiconductors. Van der Waals materials are composed of layers held weakly by van der Waals forces. This feature allows different materials to be combined into heterostructures, with fewer restrictions on growth and lattice matching. Here, Zhu et al make use of this feature to create a van der Waals magnetic tunnel junction with a semiconducting spacer, allowing for improved tunability and reduced device thickness.