MoS2 Photodetector Research Articles

Highly Sensitive Photodetectors Based on Monolayer MoS2 Field-Effect Transistors.

Molybdenum disulfide (MoS2) is a promising candidate for the development of high-performance photodetectors, due to its excellent electric and optoelectronic properties. However, most of the reported MoS2 phototransistors have adopted a back-gate field-effect transistor (FET) structure, requiring applied gate bias voltages as high as 70 V, which made it impossible to modulate each detecting device in the fabricated array. In this paper, buried-gate FETs based on CVD-grown monolayer MoS2 were fabricated and their electric and photoelectric properties were also systematically investigated. A photoresponsivity of around 6.86 A/W was obtained at 395 nm, under the conditions of zero gate bias voltage and a light power intensity of 2.57 mW/cm2. By application of a buried-gate voltage of 8 V, the photoresponsivity increased by nearly 10 times. Furthermore, the response speed of the buried-gate MoS2 FET phototransistors is measured to be around 350 ms. These results pave the way for MoS2 photodetectors in practical applications.

Improving the photoresponse performance of monolayer MoS2 photodetector via local flexoelectric effect

Strain engineering is an effective means of modulating the optical and electrical properties of two-dimensional materials. The flexoelectric effect caused by inhomogeneous strain exists in most dielectric materials, which breaks the limit of the materials’ non-centrosymmetric structure for piezoelectric effect. However, there is a lack of understanding of the impact on optoelectronic behaviour of monolayer MoS2 photodetector via local flexoelectric effect triggered by biaxial strain. In this paper, we develop a probe tip (Pt)-MoS2-Au asymmetric Schottky barrier photodetector based on conductive atomic force microscopy to investigate the impact of flexoelectric effect on the photoresponse performance. Consequently, when the probe force increases from 24 nN to 720 nN, the photocurrent, responsivity and detectivity increase 28.5 times, 29.6 times and 5.3 times at forward bias under 365 nm light illumination, respectively. These results indicate that local flexoelectric effect plays a critical role to improve the photoresponse performance of photodetector. Our approach suggests a new route to improve the performance of photodetectors by introducing local flexoelectric polarization field, offering the potential for the application of strain modulated photoelectric devices.

High-Performance Photodetectors Based on MoTe2-MoS2 van der Waals Heterostructures.

Two-dimensional (2D) materials have got extensive attention for multifunctional device applications in advanced nanoelectronics and optoelectronics, such as field-effect transistors, photodiodes, and solar cells. In our work, we fabricated MoTe2–MoS2 van der Waals heterostructure photodetectors with great performance using the mechanical exfoliation method and restack technique. It is demonstrated that our MoTe2–MoS2 heterostructure photodetector device can operate without bias voltage, possessing a low dark current (10 pA) and high photocurrent on/off ratio (>104). Importantly, the room temperature photoresponsivity of the MoTe2–MoS2 photodetector can reach 110.6 and 9.2 mA W–1 under λ = 532 and 1064 nm incident laser powers, respectively. Our results indicate that the van der Waals heterostructure based on 2D semiconducting materials is expected to play an important role in nanoscale optoelectronic applications.

Low-voltage, self-powered and broadband photodetector with Ohmic, transparent and cost-effective AZO electrodes on vertical aligned MoS2 flakes

The transparent Ohmic electrodes are the extreme necessity to develop cutting-edge broadband photodetectors. Conventional metal electrodes reflect incident light and diminish overall performance of photodetector. Here, we report cost-effective, transparent Ohmic Al-doped ZnO (AZO) electrodes to develop self-powered, highly responsive photodetectors from visible to near-infrared regions using vertically-aligned MoS2 (VA- MoS2) flakes. The MoS2 photodetector with AZO electrode (AZO-MoS2) shows a high responsivity of 40.67 A/W at 800 nm at low biasing voltage of 0.5 V. The self-driven behavior is observed in a broad range from 400 to 1100 nm with high responsivity of 38.18 mA/W at 800 nm. Moreover, AZO-MoS2 device has fast rise and decay time. To understand impact of Ohmic AZO electrode in comparison to traditional metal electrodes, we have also investigated conventional Au-MoS2 PDs fabricated under identical dimensions. The AZO-MoS2 PD demonstrated 100 times higher responsivity than conventional Au-MoS2 PD at 800 nm. We have investigated band-alignment between AZO and MoS2 using ultraviolet spectroscopy (UPS) and confirmed ohmic nature between the AZO and MoS2. These results indicate superior performance of AZO-MoS2 PD device in comparison to traditional metal electrodes.

Fabrication of Highly Photosensitive MoS2 Photodetector Films Using Rapid Electrohydrodynamic‐Jet Printing Process

AbstractMolybdenum disulfide (MoS2) is a representative transition metal dichalcogenide (TMD) that has been extensively studied as a potential semiconducting material for next generation optoelectronic applications due to its exceptional optical, electrical, and mechanical properties. However, the lack of an efficient and scalable technique for MoS2 film synthesis is a major drawback. Therefore, in this study, electrohydrodynamic (EHD) jet printed MoS2 (EJP MoS2) photodetectors are reported. The optoelectronic characteristics of the EJP MoS2 photodetector are investigated using two modes: two‐terminal and three‐terminal configuration under light illumination. For the two‐terminal mode of the EJP MoS2 photodetector, a photosensitivity of 3444% and a photoresponsivity of 1.68 A W–1 are achieved, respectively. Concurrently, the three‐terminal mode of the EJP MoS2 photodetector exhibits an improved photosensitivity (4495%) and photoresponsivity (3.78 A W–1) under gate voltage. The proposed EHD jet printing method and the EJP MoS2 based photodetector will provide a feasible solution for high performance TMDs based photonics.

Plasmonic MXene Nanoparticle-Enabled High-Performance Two-Dimensional MoS2 Photodetectors.

Two-dimensional (2D) molybdenum disulfide (MoS2) has emerged as a prospective candidate for photodetection. However, due to the surface defects formed during the synthesis, the low photoresponse of 2D MoS2 photodetectors restricts its practical applications. Here, we developed a hybrid plasmonic structure that integrates MXene nanoparticles (MNPs) and 2D MoS2. With the introduction of MNPs, light waves are concentrated on MoS2 nanosheets via a strong localized surface plasmon resonance. Consequently, MNPs-decorated MoS2 photodetectors exhibit an improved photoresponse, including a higher responsivity (20.67 A/W), a larger detectivity of 5.39 × 1012 Jones, and a maximum external quantum efficiency of over 5000%. A 150-fold enhanced detectivity (2.33 × 1012 Jones) was achieved under 635 nm light illumination in the optimized device. These results provide an alternative approach for improving the photoresponse of MoS2 photodetectors.

Enhanced visible to near-infrared photodetectors made from MoS2-based mixed-dimensional structures

Two-dimensional (2D) photodetectors based on semiconducting transitional metal chalcogenides (TMDs) have attracted much attention because of its unique mechanical and opto-electronic properties which can be integrated into nanoscale-sized opto-electronic devices and complex circuits. However, the photodetection range of 2D TMDs materials based detectors are generally limited within the visible range due to its intrinsic relatively large band-gap. In addition, 2D TMDs materials also suffers from weak light absorption inherited from their atomically thin layers, resulting in a photoresponsivity that can be further improved. Herein, by combining 2D MoS2 with zero-dimensional (0D) PbSe quantum dots (QDs) and Au nanocrystals (NCs), a novel 2D-0D photodetector (i.e., MoS2/PbSe@Au) is fabricated. Our MoS2/PbSe@Au photodetector exploits the 2D MoS2 as the conduction channels and PbSe@Au NCs as light sensitizer, which promote the absorption of the entire device and enable appreciable photodetection extending to the near-infrared (NIR). Prominently, the mixed-dimensional photodetector exhibits high responsivity of 1.22 A/W and detectivity of 1.56*109 Jones (cm·Hz1/2·W−1) at NIR (e.g., 1064 nm) compared with the MoS2 photodetector with PbSe QDs only, which are ascribed to the more efficient two-step charge transfer process between PbSe and MoS2 with the presence of Au NCs. We further identify the new carrier multiplication mechanism when comparing the photoresponse of our photodetectors at 405 nm and 635 nm. We found the extremely high EQE of MoS2/PbSe@Au photodetector at the wavelength of 405 nm (268.1%) could be ascribed to the synergism of carrier multiplication (CM) in PbSe QDs and the photo-gating effect induced by Au nanoparticles. Our study demonstrates that the novel mixed-dimensional photodetectors based on CVD-grown MoS2 may provide a new route for designing and realizing high-performance optoelectronic devices with harvesting merits of hybrid nanomaterials.

Telecom-Band Waveguide-Integrated MoS2 Photodetector Assisted by Hot Electrons

Telecom-Band Waveguide-Integrated MoS₂ Photodetector Assisted by Hot Electrons

High-performance, self-powered flexible MoS2 photodetectors with asymmetric van der Waals gaps.

With an urgent demand for low-energy-consumption and wearable devices, it is desirable to find an easy, effective, and low-cost method to fabricate self-powered flexible photodetectors with simple configurations and high-performance. Self-powered photodetectors are normally fabricated based on either two different materials or the same material in contact with two different metal electrodes. Here, a flexible MoS2 photodetector with the same Au electrodes was fabricated on a polyethylene terephthalate (PET) substrate which exhibits self-powered properties. To our knowledge, its configuration is the simplest, and the fabrication process is easy to implement. At a bias of 0 V, the photodetector exhibits a high responsivity of 431 mA W-1, a short response/recovery time of 40 ms/40 ms, and excellent flexibility. Compared with those at a bias of 2 V, a dark current is sufficiently suppressed, and the response/recovery speed is significantly improved. It is found that the driving force of the self-powered photodetector is provided by the asymmetric Schottky barriers originating from the spontaneous generation of two van der Waals gaps with different widths. The asymmetric barriers exist stably at the interfaces between the 2D material and Au electrodes as further observed for ReS2 or GaSe flakes, which show the generality of asymmetric Schottky barriers between the 2D material and Au electrodes. The discovery here thus gives a new way to generate asymmetric Schottky barriers and develop high-performance self-powered photodetectors.

High-responsivity photodetector based on scrolling monolayer MoS2 hybridized with carbon quantum dots

The monolayer MoS2 based photodetectors have been widely investigated, which show limited photoelectric performances due to its low light absorption and uncontrollable adsorbates. In this paper, we present a MoS2-based hybrid nanoscrolls device, in which one-dimensional nanoscrollsof MoS2 is hybridized with carbon quantum dots (CQDs). This device architecture effectively enhanced the photodetection performance. The photoresponsivity and detectivity values of MoS2/CQDs-NS photodetectors are respectively 1793 A W−1 and 5.97 × 1012 Jones, which are 830-fold and 268-fold higher than those of pristine MoS2 under 300 nm illumination at V ds = 5 V. This research indicates a significant progress in fabricating high-performance MoS2 photodetectors.

Fabry-Perot interference and piezo-phototronic effect enhanced flexible MoS2 photodetector

Fabry-Perot interference and piezo-phototronic effect enhanced flexible MoS2 photodetector

Monolayer MoS2 photodetectors with a buried-gate field-effect transistor structure

Unlike zero-bandgap graphene, molybdenum disulfide (MoS2) has an adjustable bandgap and high light absorption rate, hence photodetectors based on MoS2 have attracted tremendous research attention. Most of the reported MoS2 photodetectors adopted back-gate field-effect transistor (FET) structure due to its easy fabrication and modulation features. However, the back-gate FET structure requires very high gate voltage up to 100 V, and it is impossible to modulate each device in an array with this structure independently. This work demonstrated a monolayer MoS2 photodetector based on a buried-gate FET structure whose experimental results showed that both the electrical and photoelectrical properties could be well modulated by a gate voltage as low as 3 V. A photoresponsivity above 1 A W−1 was obtained under a 395 nm light-emitting diode light illumination, which is over 2 orders of magnitude higher than that of a reported back-gate photodetector based on monolayer MoS2 (7.5 mA W−1). The photoresponsivity can be further improved by increasing the buried gate voltage and source-drain voltage. These results are of significance for the practical applications of MoS2 photodetectors, especially in the low voltage and energy-saving areas.

Stretchable MoS2 Artificial Photoreceptors for E‐Skin

Abstract2D materials have been widely applied in flexible electronics but only with limited stretchability, because the metal‐halide bonding is so strong that the materials’ electronic properties will be severely influenced upon tensile strain. Here, a strategy is proposed for the fabrication of ultrastretchable MoS2 photoreceptors based on chemical vapor deposition‐grown or manually stacked multilayer MoS2. Strain‐dependent spectroscopic comparisons of multilayer versus monolayer MoS2 indicate that the strain transfer is suppressed from bottom to top layers owing to interlayer sliding, which is consistent with the density functional theory and molecular dynamics simulations. Thus, the optoelectronic properties of multilayer MoS2 can withstand larger mechanical strain than monolayer MoS2. Leveraging this mechanical feature, ten‐layer MoS2 photodetector is fabricated on polystyrene‐b‐poly (ethylene‐co‐butylene)‐b‐polystyrene elastomer, withstanding ≈50% tensile strain and presenting 32 times higher photoresponsivity than that of monolayer MoS2 under the same stretching condition. Based on large‐area bilayer MoS2 film, 5 × 5 stretchable photodetector array is demonstrated and is capable of working as artificial photoreceptors to control a robotic hand under 16% tensile strain, showing great potential in applications for 2D material‐based electronic skin.

Femtosecond Laser Irradiation-Mediated MoS2-Metal Contact Engineering for High-Performance Field-Effect Transistors and Photodetectors.

2D materials exhibit intriguing electrical and optical properties, making them promising candidates for next-generation nanoelectronic devices. However, the high contact resistance of 2D materials to electrode material often limits the ultimate performance and potential of 2D materials and devices. In this work, we demonstrate a localized femtosecond (fs) laser irradiation process to substantially minimize the resistance of MoS2-metal contacts. A reduction of the contact resistance exceeding three orders of magnitude is achieved for mechanically exfoliated MoS2, which remarkably improves the overall FET performance. The underlying mechanisms of resistance reduction are the removal of organic contamination induced by the transfer process, as well as the lowering of Schottky barrier resistance (RSB) attributed to interface Fermi level pinning (FLP) by Au diffusion, and the lowering of interlayer resistance (Rint) due to interlayer coupling enhancement by Au intercalation under fs laser irradiation. By taking advantage of the improved MoS2-metal contact behavior, a high-performance MoS2 photodetector was developed with a photoresponsivity of 68.8 A W-1 at quite a low Vds of 0.5 V, which is ∼80 times higher than the pristine multilayer photodetector. This contamination-free, site-specific, and universal photonic fabrication technique provides an effective tool for the integration of complex 2D devices, and the mechanism of MoS2-metal interface modification reveals a new pathway to engineer the 2D material-metal interface.

Optoelectronic performance characterization of MoS2 photodetectors for low frequency sensing applications

The specific advantages of implementing MoS2 and other layered semiconductors for optoelectronic biosensing and other relevant photodetection applications remain unclear. In this work, we investigate the photoresponsivity and noise characteristics of in-plane MoS2 photodetectors. This work indicates that MoS2 photodetectors exhibit lower noise equivalent power (NEP) and detectivity (D*) in comparison with commercial CdS photodetectors. In addition, the low-frequency NEP and D* values of MoS2 photodetectors exhibit a prominent dependence on the MoS2 photoactive layer thickness. We have identified the optimal MoS2 thickness in the range of 8–30 nm. We also study the photoresponse characteristics of optimized MoS2 photodetectors at several different wavelengths that are important for clinical colorimetry assays. Such an optimized photodetector shows a maximum photoresponsivity of 164.3 A/W and a minimum NEP of 3.99 × 10−17 W/Hz1/2 (and a D* of 5.01 × 1010 J) with relative variance less than 14%. This work provides a useful guideline for optimizing the photoresponse characteristics of MoS2-based optoelectronic devices, which is critical to practical low-frequency optoelectronic biosensing applications.

Investigation of charge transport and band alignment of MoS2-ReS2 heterointerface for high performance and self-driven broadband photodetection

Two dimensional (2D) van der Waals heterostructures are becoming one of the ascendant research areas for semiconducting device application owing to their remarkable optoelectronic properties, which allows more functioning ability beyond its individual constituent. 2D layered materials can be easily integrated and form heterostructure due to the dangling bond free surfaces. However, for novel optoelectronic device applications, the understanding of charge carrier dynamics at the interface of heterostructures is critical and essential. Here, we demonstrate the charge transport behaviour and energy level band alignment at MoS2-ReS2 heterointerface. Interlayer coupling and charge transport behaviour are investigated by Raman and photoluminescence spectroscopy. The photoelectron spectroscopy confirms type Ⅱ band alignment between MoS2-ReS2 interface, which is required for efficient separation and transportation of charge carriers. As a proof of concept, a highly sensitive, self-biased broadband photodetector is fabricated with a responsivity of 42.61 A/W at a low bias of 1 V under the illumination of 800 nm, which is 16 fold higher than the reference pristine MoS2 photodetector. Moreover, fast rise/decay transient photoresponse (20/19 ms) strongly advocate the spatial separation of charge carriers across the interface. Our proposed work establishes the MoS2 and ReS2 as promising candidates for next-generation broadband photodetector applications.

Lattice Defect Engineering Enables Performance-Enhanced MoS2 Photodetection through a Paraelectric BaTiO3 Dielectric.

Carrier mobility and density are intrinsically important in nanophoto/electronic devices. High-dielectric-constant coupled polarization-field gate ferroelectrics are frequently studied and partially capable in achieving large-scale tuning of photoresponse, but their light absorption and carrier density seem generally ineffective. This raises questions about whether a similarly high-dielectric-constant paraelectric gate dielectric could enable tuning and how the principles involved could be established. In this study, by deliberately introducing lattice defects in high-dielectric-constant paraelectric, cubic BaTiO3 (c-BTO) was explored to fabricate MoS2 photodetectors with ultrahigh detection ability and outstanding field-effect traits. An organic-metal-based spin-coating cum annealing method was used for the c-BTO synthesis, with an optimized thickness (300 nm), by introducing lattice defects properly but maintaining a large dielectric constant (55 at 1k Hz) and low dielectric loss (0.06 at 1k Hz), which renders the enhanced visible-light region absorption. As a result of the synergistically enhanced mobility and photoabsorption, the MoS2/BTO FET exhibits promising merits, for example, on/off ratio, subthreshold swing, and mobilities for high-performance photodetectors with excellent responsivity (600 AW-1) and detectivity (1.25 × 1012 Jones). Thus, this work facilitates the establishment of a lattice defect induced sub-bandgap absorption landmap for synergistically enhanced photoresponse for high-performance photodetector exploration.

Enhancement of Photodetective Properties on Multilayered MoS2 Thin Film Transistors via Self-Assembled Poly-L-Lysine Treatment and Their Potential Application in Optical Sensors.

Photodetectors and display backplane transistors based on molybdenum disulfide (MoS2) have been regarded as promising topics. However, most studies have focused on the improvement in the performances of the MoS2 photodetector itself or emerging applications. In this study, to suggest a better insight into the photodetector performances of MoS2 thin film transistors (TFTs), as photosensors for possible integrated system, we performed a comparative study on the photoresponse of MoS2 and hydrogenated amorphous silicon (a-Si:H) TFTs. As a result, in the various wavelengths and optical power ranges, MoS2 TFTs exhibit 2~4 orders larger photo responsivities and detectivities. The overall quantitative comparison of photoresponse in single device and inverters confirms a much better performance by the MoS2 photodetectors. Furthermore, as a strategy to improve the field effect mobility and photoresponse of the MoS2 TFTs, molecular doping via poly-L-lysine (PLL) treatment was applied to the MoS2 TFTs. Transfer and output characteristics of the MoS2 TFTs clearly show improved photocurrent generation under a wide range of illuminations (740~365 nm). These results provide useful insights for considering MoS2 as a next-generation photodetector in flat panel displays and makes it more attractive due to the fact of its potential as a high-performance photodetector enabled by a novel doping technique.

(Invited) Optically-Active Zero-Dimensional Graphene Quantum Dots with MoS2 for Photodetection

With its superior electronic properties, large surface area, high mechanical strength-to-weight ratio, exceptional charge carrier mobility reaching the ballistic limit in certain cases, graphene is a material of immense technological importance. However, compared to other two-dimensional (2D) van der Waals solids, such as transition metal dichalcogenides (TMDCs) and black phosphorus, an atomic membrane of graphene absorbs less than about 2% of the incoming light due to its low light absorption cross-section, and lack of a bandgap. However, when sheets of graphene are physically confined into nanoscale dimensions, either as graphene nanoribbons or zero-dimensional (0D) structures, such as graphene quantum dots (GQDs), a band gap in such structures is induced due to quantum confinement. Additionally, semiconducting 2D materials such as MoS2, exhibit a distinct and well defined band gap ranging from 1.3 eV to 1.8 eV, from bulk to monolayers. In this work, the hybrid structure of 0D graphene quantum dots (GQDs) and semiconducting 2D MoS2 has been investigated that exhibit outstanding properties for optoelectronic devices surpassing the limitations of MoS2 photodetectors where the GQDs extend the optical absorption into the near-UV regime. A tunable laser revealed the photocurrent to be maximal at lower wavelengths in the near ultra-violet (UV) over the 400 – 1100 nm spectral range, where the responsivity of the hybrid GQDs/MoS2 was ~ 775 AW-1. Time-resolved measurements of the photocurrent for the hybrid devices also resulted in enhancement of the switching dynamics with switching time constants far improved compared to bare MoS2. From our promising results, we conclude that the GQDs exhibit a sizable bandgap upon optical excitation, where photocarriers are injected into the MoS2 films, endowing the hybrids with long carrier life-times to enable efficient light absorption beyond the visible and into the near-UV regime. The GQD-MoS2 structure is thus an enabling platform for high-performance photodetectors, optoelectronic circuits and quantum devices.

Flexible and highly responsive photodetectors based on heterostructures of MoS2 and all-carbon transistors

Heterostructures of graphene and transition-metal dichalcogenides (TMDCs) are promising candidates for high-performance flexible photodetectors because of their high photoresponsivity and detectivity. However, the mechanical stability of current flexible photodetectors is limited, due to a mechanical mismatch between their two-dimensional channel materials and metallic contacts. Herein, we develop a type of mechanically stable, highly responsive, and flexible photodetector by integrating MoS2 and all-carbon transistors. By combining the high mobility of graphene with the strong light–matter interactions of MoS2, our heterostructure photodetector exhibits a greatly improved photoresponse performance, compared with individual graphene or MoS2 photodetectors. In addition, the mechanical properties of the all-carbon electrodes are a good match for those of the active two-dimensional channels, resulting in greatly improved electrical stability of the heterostructure photodetector under mechanical deformation. These capabilities make our heterostructure photodetector a promising candidate for flexible photodetection and photoimaging applications.