Two-dimensional transition metal dichalcogenides (2D TMDs) have attracted much attention in the field of optoelectronics due to their tunable bandgaps, strong interaction with light and tremendous capability for developing diverse van der Waals heterostructures (vdWHs) with other materials. Molybdenum disulfide (MoS2) atomic layers which exhibit high carrier mobility and optical transparency are very suitable for developing ultra-broadband photodetectors to be used from surveillance and healthcare to optical communication. This review provides a brief introduction to TMD-based photodetectors, exclusively focused on MoS2-based photodetectors. The current research advances show that the photoresponse of atomic layered MoS2 can be significantly improved by boosting its charge carrier mobility and incident light absorption via forming MoS2 based plasmonic nanostructures, halide perovskites–MoS2 heterostructures, 2D–0D MoS2/quantum dots (QDs) and 2D–2D MoS2 hybrid vdWHs, chemical doping, and surface functionalization of MoS2 atomic layers. By utilizing these different integration strategies, MoS2 hybrid heterostructure-based photodetectors exhibited remarkably high photoresponsivity raging from mA W−1 up to 1010 A W−1, detectivity from 107 to 1015 Jones and a photoresponse time from seconds (s) to nanoseconds (10−9 s), varying by several orders of magnitude from deep-ultraviolet (DUV) to the long-wavelength infrared (LWIR) region. The flexible photodetectors developed from MoS2-based hybrid heterostructures with graphene, carbon nanotubes (CNTs), TMDs, and ZnO are also discussed. In addition, strain-induced and self-powered MoS2 based photodetectors have also been summarized. The factors affecting the figure of merit of a very wide range of MoS2-based photodetectors have been analyzed in terms of their photoresponsivity, detectivity, response speed, and quantum efficiency along with their measurement wavelengths and incident laser power densities. Conclusions and the future direction are also outlined on the development of MoS2 and other 2D TMD-based photodetectors.

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A review of molybdenum disulfide (MoS2) based photodetectors: from ultra-broadband, self-powered to flexible devices

Atomically thin transition metal dichalcogenides have emerged as promising candidates for sensitive photodetection. Here, we report a photoconductivity study of biased mono- and bilayer molybdenum disulfide field-effect transistors. We identify photovoltaic and photoconductive effects, which both show strong photogain. The photovoltaic effect is described as a shift in transistor threshold voltage due to charge transfer from the channel to nearby molecules, including SiO2 surface-bound water. The photoconductive effect is attributed to the trapping of carriers in band tail states in the molybdenum disulfide itself. A simple model is presented that reproduces our experimental observations, such as the dependence on incident optical power and gate voltage. Our findings offer design and engineering strategies for atomically thin molybdenum disulfide photodetectors, and we anticipate that the results are generalizable to other transition metal dichalcogenides as well.

Mechanisms of photoconductivity in atomically thin MoS2

X.G., X.Y., and D.P. contributed equally to this work. The authors thank the support from Singapore National Research Foundation, Competitive Research Program (NRF-CRP18-2017-02 and NRF–CRP19–2017–01), A*Star AME Programmatic Grant under Grant A18A7b0058, Singapore Ministry of Education Tier 2 Program (MOE2016-T2-1-128), and National Natural Science Foundation of China (61704082) and Natural Science Foundation of Jiangsu Province (BK20170851).

Recent Progress in Short- to Long-Wave Infrared Photodetection Using 2D Materials and Heterostructures

The evolutionary success in information technology has been sustained by the rapid growth of sensor technology. Recently, advances in sensor technology have promoted the ambitious requirement to build intelligent systems that can be controlled by external stimuli along with independent operation, adaptivity, and low energy expenditure. Among various sensing techniques, field-effect transistors (FETs) with channels made of two-dimensional (2D) materials attract increasing attention for advantages such as label-free detection, fast response, easy operation, and capability of integration. With atomic thickness, 2D materials restrict the carrier flow within the material surface and expose it directly to the external environment, leading to efficient signal acquisition and conversion. This review summarizes the latest advances of 2D-materials-based FET (2D FET) sensors in a comprehensive manner that contains the material, operating principles, fabrication technologies, proof-of-concept applications, and prototypes. First, a brief description of the background and fundamentals is provided. The subsequent contents summarize physical, chemical, and biological 2D FET sensors and their applications. Then, we highlight the challenges of their commercialization and discuss corresponding solution techniques. The following section presents a systematic survey of recent progress in developing commercial prototypes. Lastly, we summarize the long-standing efforts and prospective future development of 2D FET-based sensing systems toward commercialization.

Two-Dimensional Field-Effect Transistor Sensors: The Road toward Commercialization.

Photodetectors based on transition metal dichalcogenides (TMDs) have been widely reported in the literature and molybdenum disulfide (MoS2) has been the most extensively explored for photodetection applications. The properties of MoS2, such as direct band gap transition in low dimensional structures, strong light-matter interaction and good carrier mobility, combined with the possibility of fabricating thin MoS2 films, have attracted interest for this material in the field of optoelectronics. In this work, MoS2-based photodetectors are reviewed in terms of their main performance metrics, namely responsivity, detectivity, response time and dark current. Although neat MoS2-based detectors already show remarkable characteristics in the visible spectral range, MoS2 can be advantageously coupled with other materials to further improve the detector performance Nanoparticles (NPs) and quantum dots (QDs) have been exploited in combination with MoS2 to boost the response of the devices in the near ultraviolet (NUV) and infrared (IR) spectral range. Moreover, heterostructures with different materials (e.g., other TMDs, Graphene) can speed up the response of the photodetectors through the creation of built-in electric fields and the faster transport of charge carriers. Finally, in order to enhance the stability of the devices, perovskites have been exploited both as passivation layers and as electron reservoirs.

MoS2 Based Photodetectors: A Review.

Extremely Low Dark Current MoS2 Photodetector via 2D Halide Perovskite as the Electron Reservoir

Two-dimensional (2D) perovskite materials are a promising platform to construct high performance photodetectors due to their novel structure, high stability, resistance to ion migration and decent light harvesting ability. However, the detection range of 2D perovskite photodetectors is limited due to their large bandgap. Here, self-trapped states with a lower bandgap were created by introducing Sn into a 2D perovskite ((C6H5C2H4NH3)2PbI4, (PEA)2PbI4). Although previously the excitons in the self-trapped states have been regarded as localized excitons, an obvious photocurrent generated by the dissociation of excitons in self-trapped states has been observed. With this property, the detection range of 2D perovskite photodetectors has been successfully extended. Additionally, the special 2D structure of (PEA)2PbI4 endows the device with high stability and great resistance for ion migration to endure long-term (over 1000 s) consistent work without degradation in performance. This facile doping method for extending the detection range of 2D perovskite photodetectors will greatly broaden their application potential.

Dapeng Li

Papers

Extremely Low Dark Current MoS2 Photodetector via 2D Halide Perovskite as the Electron Reservoir

Detection range extended 2D Ruddlesden–Popper perovskite photodetectors

A luminescent lanthanide MOF as highly selective and sensitive fluorescent probe for nitrobenzene and Fe3+