Two-dimensional (2D) Ruddlesden-Popper perovskites are currently drawing significant attention as highly-stable photoactive materials for optoelectronic applications. However, the insulating nature of organic ammonium layers in 2D perovskites results in poor charge transport and limited performance. Here, we demonstrate that Al2O3/2D perovskite heterostructure can be utilized as photoactive dielectric for high-performance MoS2 phototransistors. The type-II band alignment in 2D perovskites facilitates effective spatial separation of photo-generated carriers, thus achieving ultrahigh photoresponsivity of >108 A/W at 457 nm and >106 A/W at 1064 nm. Meanwhile, the hysteresis loops induced by ionic migration in perovskite and charge trapping in Al2O3 can neutralize with each other, leading to low-voltage phototransistors with negligible hysteresis and improved bias stress stability. More importantly, the recombination of photo-generated carriers in 2D perovskites depends on the external biasing field. With an appropriate gate bias, the devices exhibit wavelength-dependent constant photoresponsivity of 103–108 A/W regardless of incident light intensity.

Two-dimensional (2D) materials such as WSe 2 are potential for advanced electronics because of their ultra-thin geometry and unique electrical properties. Herein, a simplified high-performance WSe 2 complementary inverter based on a buried gate is demonstrated on an individual ambipolar WSe 2 flake, in which both n- and p-type WSe 2 transistors are achieved by local doping. The n-type doping is induced by the donors of benzyl viologen, showing an electron mobility of 28.1 cm 2 /V.s. In contrast, the p-type one is realized by Ozone exposure with a high mobility of 36.8 cm 2 /V.s. The buried gate enables enhanced electrostatic coupling, with a supply voltage (V dd ) of 5 V, and the complementary inverter demonstrates a voltage gain beyond 32, almost ideal noise margin approaching 0.5V dd and low static power consumption. This work paves the way to achieve high-performance 2D material complementary inverters with simplified fabrication process.

Organic–inorganic hybrid perovskites (PVKs) have recently emerged as attractive materials for photodetectors. However, the poor stability and low electrical conductivity still restrict their practical utilization. Owing to the quantum‐well feature of two‐dimensional (2D) Ruddlesden–Popper PVKs (2D PVKs), a promising quasi‐2D PVK/indium gallium zinc oxide (IGZO) heterostructure phototransistor can be designed. By using a simple ligand‐exchange spin‐coating method, quasi‐2D PVK fabricated on flexible substrates exhibits a desirable type‐II energy band alignment, which facilitates effective spatial separation of photoexcited carriers. The device exhibits excellent photoresponsivity values of >105 A W−1 at 457 nm, and broadband photoresponse (457–1064 nm). By operating the device in the depletion regime, the specific detectivity is found to be 5.1 × 1016 Jones, which is the record high value among all PVK‐based photodetectors reported to date. Due to the resistive hopping barrier in the quasi‐2D PVK, the device can also work as an optoelectronic memory for near‐infrared information storage. More importantly, the easy manufacturing process is highly beneficial, enabling large‐scale and uniform quasi‐2D PVK/IGZO hybrid films for detector arrays with outstanding ambient and operation stabilities. All these findings demonstrate the device architecture here provides a rational avenue to the design of next‐generation flexible photodetectors with unprecedented sensitivity.

Gate dielectrics with an equivalent oxide thickness of only one nanometre can be grown on two-dimensional semiconductors with the help of a monolayer molecular crystal.

As compared with epitaxial semiconductor devices, two-dimensional (2D) heterostructures offer alternative facile platforms for many optoelectronic devices. Among them, photovoltaic based photodetectors can give fast response, while the photogate devices can lead to high responsivity. Here, we report a 2D photogate photodiode, which combines the benefits of 2D black phosphorus/MoS2 photodiodes with the emerging potential of perovskite, to achieve both fast response and high responsivity. This device architecture is constructed based on the fast photovoltaic operation together with the high-gain photogating effect. Under reverse bias condition, the device exhibits high responsivity (11 A/W), impressive detectivity (1.3 × 1012 Jones), fast response (150/240 μs), and low dark current (3 × 10–11 A). All these results are already much better in nearly all aspects of performance than the previously reported 2D photodiodes operating in reverse bias, achieving the optimal balance between all figure-of-merits. Importantly, with a zero bias, the device can also yield high detectivity (3 × 1011 Jones), ultrahigh light on/off ratio (3 × 107), and extremely high external quantum efficiency (80%). This device architecture thus has a promise for high-efficiency photodetection and photovoltaic energy conversion.

For atomically thin two-dimensional materials, interfacial effects may dominate the entire response of devices, because most of the atoms are in the interface/surface. Graphene/sapphire has great application in electronic devices and semiconductor thin-film growth, but the nature of this interface is largely unknown. Here we find that the sapphire surface has a strong interaction with some of the carbon atoms in graphene to form a C-O-Al configuration, indicating that the interface interaction is no longer a simple van der Waals interaction. In addition, the structural relaxation of sapphire near the interface is significantly suppressed and very different from that of a bare sapphire surface. Such an interfacial C-O-Al bond is formed during graphene growth at high temperature. Our study provides valuable insights into understanding the electronic structures of graphene on sapphire and remote control of epitaxy growth of thin films by using a graphene–sapphire substrate.

Metal/semiconductor contact is a significant constraint in short‐channel field effect transistors (FETs) comprising black phosphorus (BP) and other 2D semiconductors. Due to the pinning effect at metal/2D semiconductor interface, the Schottky barrier usually does not follow the Schottky–Mott rule, resulting in thickness‐dependent FET performance. In this work, the Schottky barrier in BP FETs is investigated via theory calculation and electrical measurement. A simple metal/BP contact model is presented based upon thickness‐dependent electrical characteristics of BP FETs. The model considers the Schottky barrier as a combined effect of the Schottky–Mott rule and the pinning effect and provides a feasibility to track the conducting behavior of other 2D semiconductor FETs.

Artificial superlattices, based on van der Waals heterostructures of two-dimensional atomic crystals such as graphene or molybdenum disulfide, offer technological opportunities beyond the reach of existing materials1,2,3. Typical strategies for creating such artificial superlattices rely on arduous layer-by-layer exfoliation and restacking, with limited yield and reproducibility4,5,6,7,8. The bottom-up approach of using chemical-vapour deposition produces high-quality heterostructures9,10,11 but becomes increasingly difficult for high-order superlattices. The intercalation of selected two-dimensional atomic crystals with alkali metal ions offers an alternative way to superlattice structures12,13,14, but these usually have poor stability and seriously altered electronic properties. Here we report an electrochemical molecular intercalation approach to a new class of stable superlattices in which monolayer atomic crystals alternate with molecular layers. Using black phosphorus as a model system, we show that intercalation with cetyl-trimethylammonium bromide produces monolayer phosphorene molecular superlattices in which the interlayer distance is more than double that in black phosphorus, effectively isolating the phosphorene monolayers. Electrical transport studies of transistors fabricated from the monolayer phosphorene molecular superlattice show an on/off current ratio exceeding 107, along with excellent mobility and superior stability. We further show that several different two-dimensional atomic crystals, such as molybdenum disulfide and tungsten diselenide, can be intercalated with quaternary ammonium molecules of varying sizes and symmetries to produce a broad class of superlattices with tailored molecular structures, interlayer distances, phase compositions, electronic and optical properties. These studies define a versatile material platform for fundamental studies and potential technological applications.

The van der Waals integration of atomically thin two-dimensional (2D) materials can enable a new generation of tunable optoelectronic devices, in which the photocarrier generation, separation and extraction can be modulated by an external gate potential. However, studies to date only show a limited modulation due to non-ideal band alignment and the lack independent modulation of distinct 2D layers in the van der Waals heterojunction. Here report the construction of a WSe2/GeSe heterojunction photodiode with type-II band alignment, in which the value of the conduction band and valence band edge in WSe2 is approximately equal to that of GeSe. What's more, the Fermi level of GeSe remains relative stationary and that of WSe2 can be modulated across the entire band gap by an external gate-voltage, thus rendering widely tunable open-circuit voltages from positive (+ 0.7 V) to negative (− 0.1 V). We further show the photoresponsivity can be modulated by the gate-voltage with a factor of 105, which is similar to the current switching ratio in traditional field-effect transistors, opening up exciting potential for photonic logic circuits.

In order to realize the promising potential of MoS2 as the alternative channel material, it is essential to achieve high‐performance top‐gated MoS2 field‐effect transistors (FETs), especially since the back‐gated counterparts cannot control the device individually. Although uniform high‐k dielectric films, such as HfO2, can be obtained through the introduction of artificial nucleation sites on the MoS2 channel to fabricate top‐gated FETs, this would inevitably degrade their channel/dielectric interface quality, induce significant charged impurity scattering and lower carrier mobility. In this work, MoS2 FETs are fabricated using a self‐aligned nanowire top‐gate, which can effectively reduce the charged impurity scattering on the surface of MoS2. Specifically, the fabricated short‐channel devices exhibit impressive electrical performances, such as the high on/off current ratio, low interface trap density, and near‐ideal subthreshold slope at room temperature. In addition, the short channel effect is systematically analyzed, which indicates that the phonon scattering can be the dominant scattering mechanism in the devices when the amount of charged impurities is effectively reduced with the self‐aligned nanowire gate. All these provide an enhanced fabrication scheme to attain top‐gated short‐channel devices with the optimized interface and potentially to explore their corresponding performance limits.