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Understanding the fundamental charge carrier dynamics is of great significance for photodetectors with both high speed and high responsivity. Devices based on two-dimensional (2D) transition metal dichalcogenides can exhibit picosecond photoresponse speed. However, 2D materials naturally have low absorption, and when increasing thickness to gain higher responsivity, the response time usually slows to nanoseconds, limiting their photodetection performance. Here, by taking time-resolved photocurrent measurements, we demonstrated that graphene/MoTe2 van der Waals heterojunctions realize a fast 10 ps photoresponse time owing to the reduced average photocurrent drift time in the heterojunction, which is fundamentally distinct from traditional Dirac semimetal photodetectors such as graphene or Cd3As2 and implies a photodetection bandwidth as wide as 100 GHz. Furthermore, we found that an additional charge carrier transport channel provided by graphene can effectively decrease the photocurrent recombination loss to the entire device, preserving a high responsivity in the near-infrared region. Our study provides a deeper understanding of the ultrafast electrical response in van der Waals heterojunctions and offers a promising approach for the realization of photodetectors with both high responsivity and ultrafast electrical response.

Optoelectronic synaptic elements are emerging functional devices for the vigorous development of advanced neuromorphic computing technology in the post-Moore era. However, optoelectronic devices based on transition metal dichalcogenides (TMDs) are limited to their poor mobilities and weak light-matter interactions, which still hardly exhibit superior device performances in the application of artificial synapses. Here, we demonstrate the successful fabrication of Au nanoparticle-coupled MoS2 heterostructures via chemical vapor deposition (CVD), where the light absorption of MoS2 is greatly enhanced and engineered by plasmonic effects. Hot electrons are excited from Au nanoparticles, and then injected into MoS2 semiconductors under the light illumination. The plasmonically-engineered photo-gating effect at the metal-semiconductor junction is demonstrated to create optoelectronic devices with excellent synaptic behaviors, especially in ultra-sensitive excitatory postsynaptic current (EPSC, 9.6 × 10−3 nA@3.4 nW·cm−2), ultralow energy consumption (34.7 pJ), long-state retention time (> 1,000 s), and tunable synaptic plasticity transitions. The material system of Au-nanoparticles coupled TMDs presents unique advantages for building artificial synapses, which may lead the future development of neuromorphic electronics in optical information sensing and learning.

van der Waals (vdW) vertical p-n junctions based on two-dimensional (2D) materials have shown great potential in flexible, self-driven, high-efficiency electronic and optoelectronic applications. However, due to the complex nucleation dynamics, the controllable synthesis of vertical heterostructures remains a daunting challenge. Here, we report the controlled growth of vertical GaSe/MoS2 p-n heterojunctions via a liquid gallium (Ga)-assisted chemical vapor deposition method. The growth mechanism can be interpreted by theoretical calculations based on the Burton-Cabrera-Frank theory. By analyzing the diffusion barriers and the Ehrlich-Schwoebel barriers of adatoms, we found that the growth modes between vertical and lateral can be precisely switched by means of adjusting the amount of Ga. Based on the achieved high-quality vertical GaSe/MoS2 p-n heterojunctions, photosensing devices are further designed and systematically investigated. Upon light illumination, prominent photovoltaic effects with large open-circuit voltage (0.61 V) and broadband detection capability from 375 to 633 nm are observed, which can further be employed for self-powered photodetection with high responsivity (900 mA/W) and fast response speed (5 ms). The developed liquid-metal-assisted strategy provides an effective method for controllable synthesis of vdW heterostructures and will give impetus to their applications in high-performance optoelectronic device.

van der Waals (vdW) vertical p-n junctions based on two-dimensional (2D) materials have shown great potential in flexible, self-driven, high-efficiency electronic and optoelectronic applications. However, due to the complex nucleation dynamics, the controllable synthesis of vertical heterostructures remains a daunting challenge. Here, we report the controlled growth of vertical GaSe/MoS

Multifunctional reconfigurable devices, with higher information capacity, smaller size, and more functions, are urgently needed and draw most attention in frontiers in information technology. 2D semiconductors, ascribing to ultrathin body and easy electrostatic control, show great potential in developing reconfigurable functional units. This work proposes a novel double-gate field-effect transistor architecture with equal top and bottom gate (TG and BG) and realizes flexible optimization of the subthreshold swing (SS) and threshold voltage (V

The development of optoelectronic devices requires breakthroughs in new material systems and novel device mechanisms, and the demand recently changes from the detection of signal intensity and responsivity to the exploration of sensitivity of polarized state information. Two-dimensional (2D) materials are a rich family exhibiting diverse physical and electronic properties for polarization device applications, including anisotropic materials, valleytronic materials, and other hybrid heterostructures. In this review, we first review the polarized-light-dependent physical mechanism in 2D materials, then present detailed descriptions in optical and optoelectronic properties, involving Raman shift, optical absorption, and light emission and functional optoelectronic devices. Finally, a comment is made on future developments and challenges. The plethora of 2D materials and their heterostructures offers the promise of polarization-dependent scientific discovery and optoelectronic device application.

Multifunctional reconfigurable devices, with higher information capacity, smaller size, and more functions, are urgently needed and draw most attention in frontiers in information technology. 2D semiconductors, ascribing to ultrathin body and easy electrostatic control, show great potential in developing reconfigurable functional units. This work proposes a novel double-gate field-effect transistor architecture with equal top and bottom gate (TG and BG) and realizes flexible optimization of the subthreshold swing (SS) and threshold voltage (VTH ). While the TG and BG are used simultaneously, as a single gate to drive the transistor, ultralow average SS value of 65.5 mV dec-1 can be obtained in a large current range over 104 , enabling the application in high gain inverter. While one gate is used to initialize the channel doping, full logic swing inverter circuit with high noise margin (over 90%) is demonstrated. Such device prototype is further extended for designing reconfigurable logic applications and can be dynamically switched and well maintained between binary and ternary logics. This study provides important concept and device prototype for future multifunctional logic applications.

Substitutional doping has proved to be one of the most important approaches to tune and improve the opto-electronic performance of traditional semiconductors. Similarly, controllable substitution of cations in two-dimensional layered materials can effectively modify and manipulate the band structures, which help to explore sciences and broaden the related applications. In this paper, the salt-assisted one-step chemical vapor deposition method was used to achieve Re substitution in MoS2 monolayers. High-resolution scanning transmission electron microscopy confirms the substitution of Re atoms in Mo sites. X-ray photoelectron spectroscopy and micro-photoluminescence (PL) characterization studies suggest that the Re substitution introduces typical n-type doping in MoS2 monolayers, resulting in the distinct many-body interactions in the doped sample with a higher trion ratio than in the pristine sample in the wide temperature window. The result is further confirmed by the shorter recombination lifetime observed in the Re-doped sample acquired by time-resolved PL measurements. More intriguingly, the circularly polarized PL characterization studies demonstrate that Re doping can improve the valley polarization of the MoS2 monolayer. Our work provides a deep understanding of the optical properties and the associated many-body interactions in the Re-doped MoS2 system and offers a potential way to enhance the valley polarization for spin-/valley-photonic applications.