MoTe2

/Tag: MoTe2

Ultrahigh‐Sensitive Broadband Photodetectors Based on Dielectric Shielded MoTe2/Graphene/SnS2 p–g–n Junctions

2018-12-15T22:33:56+00:00December 15th, 2018|Categories: Publications|Tags: , , , |

h‐BN/MoTe2/graphene/SnS2/h‐BN van der Waals heterostructure photodetectors present an extraordinary broadband responsivity exceeding 2.6 × 103 A W−1 and detectivity up to ≈1013 Jones in a wide spectrum, which is attributed to the enhanced light absorption and high‐effective exciton dissociation originated from the vertical built‐in electric field and multiple photoactive layers in the unique heterostructures. Abstract 2D atomic sheets of transition metal dichalcogenides (TMDs) have a tremendous potential for next‐generation optoelectronics since they can be stacked layer‐by‐layer to form van der Waals (vdW) heterostructures. This allows not only bypassing difficulties in heteroepitaxy of lattice‐mismatched semiconductors of desired functionalities but also providing a scheme to design new optoelectronics that can surpass the fundamental limitations on their conventional semiconductor counterparts. Herein, a novel 2D h‐BN/p‐MoTe2/graphene/n‐SnS2/h‐BN p–g–n junction, fabricated by a layer‐by‐layer dry transfer, demonstrates high‐sensitivity, broadband photodetection at room temperature. The combination of the MoTe2 and SnS2 of complementary bandgaps, and the graphene interlayer provides a unique vdW heterostructure with a vertical built‐in electric field for high‐efficiency broadband light absorption, exciton dissociation, and carrier transfer. The graphene interlayer plays a critical role in enhancing sensitivity and broadening the spectral range. An optimized device containing 5−7‐layer graphene has been achieved and shows an extraordinary responsivity exceeding 2600 A W−1 with fast photoresponse and specific detectivity up to ≈1013 Jones in the ultraviolet–visible–near‐infrared spectrum. This result suggests that the vdW p–g–n junctions containing multiple photoactive TMDs can provide a viable approach toward future ultrahigh‐sensitivity and broadband photonic detectors.

Published in: "Advanced Materials".

Ultrahigh‐Sensitive Broadband Photodetectors Based on Dielectric Shielded MoTe2/Graphene/SnS2 p–g–n Junctions

2018-12-15T10:34:09+00:00December 15th, 2018|Categories: Publications|Tags: , , , |

h‐BN/MoTe2/graphene/SnS2/h‐BN van der Waals heterostructure photodetectors present an extraordinary broadband responsivity exceeding 2.6 × 103 A W−1 and detectivity up to ≈1013 Jones in a wide spectrum, which is attributed to the enhanced light absorption and high‐effective exciton dissociation originated from the vertical built‐in electric field and multiple photoactive layers in the unique heterostructures. Abstract 2D atomic sheets of transition metal dichalcogenides (TMDs) have a tremendous potential for next‐generation optoelectronics since they can be stacked layer‐by‐layer to form van der Waals (vdW) heterostructures. This allows not only bypassing difficulties in heteroepitaxy of lattice‐mismatched semiconductors of desired functionalities but also providing a scheme to design new optoelectronics that can surpass the fundamental limitations on their conventional semiconductor counterparts. Herein, a novel 2D h‐BN/p‐MoTe2/graphene/n‐SnS2/h‐BN p–g–n junction, fabricated by a layer‐by‐layer dry transfer, demonstrates high‐sensitivity, broadband photodetection at room temperature. The combination of the MoTe2 and SnS2 of complementary bandgaps, and the graphene interlayer provides a unique vdW heterostructure with a vertical built‐in electric field for high‐efficiency broadband light absorption, exciton dissociation, and carrier transfer. The graphene interlayer plays a critical role in enhancing sensitivity and broadening the spectral range. An optimized device containing 5−7‐layer graphene has been achieved and shows an extraordinary responsivity exceeding 2600 A W−1 with fast photoresponse and specific detectivity up to ≈1013 Jones in the ultraviolet–visible–near‐infrared spectrum. This result suggests that the vdW p–g–n junctions containing multiple photoactive TMDs can provide a viable approach toward future ultrahigh‐sensitivity and broadband photonic detectors.

Published in: "Advanced Materials".

Excitonic Complexes and Optical Gain in Two-Dimensional Molybdenum Ditelluride Well below Mott Transition. (arXiv:1812.04296v1 [cond-mat.mes-hall])

2018-12-12T02:29:27+00:00December 12th, 2018|Categories: Publications|Tags: , |

Strong Coulomb interaction in 2D materials provides unprecedented opportunities for studying many key issues of condensed matter physics, such as co-existence and mutual conversions of excitonic complexes, fundamental optical processes associated with their conversions, and their roles in the celebrated Mott transition. Recent lasing demonstrations in 2D materials raise important questions about the existence and origin of optical gain and possible roles of excitonic complexes. While lasing occurred at extremely low densities dominated by various excitonic complexes, optical gain was observed in the only experiment at densities several orders of magnitude higher, exceeding the Mott density. Here, we report a new gain mechanism involving charged excitons or trions well below the Mott density in 2D molybdenum ditelluride. Our combined experimental and modeling study not only reveals the complex interplays of excitonic complexes well below the Mott transition, but also provides foundation for lasing at extremely low excitation levels, important for future energy efficient photonic devices.

Published in: "arXiv Material Science".

Optical image-based thickness characterization of atomically thin nanomaterials using computer vision techniques. (arXiv:1812.03198v1 [cond-mat.mtrl-sci])

2018-12-11T02:29:30+00:00December 11th, 2018|Categories: Publications|Tags: , |

The main objective of this study was to develop a novel method of characterizing nanomaterials based on the number of layers without the aid of state-of-the-art electron and force microscopes. While previous research groups have attempted to establish a correlation between optical image contrast and layer number for inferring layer numbers of nanomaterials with already well-known software such as ImageJ and Gwyddion SPM Analysis, the work for this study strived to automate the image contrast-based characterization of the layer numbers using computer vision algorithms. After acquiring the necessary data points using graphene samples from another study and nanoscale MoTe2 samples through an experimental method consisted of using both ImageJ and Gwyddion, curve fitting in RStudio was used to create quadratic models that were incorporated in a computer vision method composed of three algorithms. In total, 12 MoTe2 and 16 graphene samples were used in 28 test trials in order to determine the efficiencies of the algorithms in layer number characterization. Ultimately, a success rate of 89% was obtained with an average overall run time of 15 seconds for the computer vision method. As a consequence, this computational method may be faster, more effective, and more cost-effective than current widely used electron, atomic force, and optical microscopy techniques.

Published in: "arXiv Material Science".

Electric-field induced structural transition in vertical MoTe<sub>2</sub>- and Mo<sub>1–x</sub>W<sub>x</sub>Te<sub>2</sub>-based resistive memories

2018-12-10T18:34:33+00:00December 10th, 2018|Categories: Publications|Tags: |

Electric-field induced structural transition in vertical MoTe2- and Mo1–xWxTe2-based resistive memoriesElectric-field induced structural transition in vertical MoTe<sub>2</sub>- and Mo<sub>1–x</sub>W<sub>x</sub>Te<sub>2</sub>-based resistive memories, Published online: 10 December 2018; doi:10.1038/s41563-018-0234-yA vertical electric field is shown to induce reversible transitions between a semiconducting 2H phase, a distorted transient structure and a conducting Td phase in MoTe2 and Mo1–xWxTe2 multilayers, and used to realize vertical resistive random access memories.

Published in: "Nature Materials".

Memristors with distorted structures

2018-12-10T18:34:32+00:00December 10th, 2018|Categories: Publications|Tags: |

Memristors with distorted structuresMemristors with distorted structures, Published online: 10 December 2018; doi:10.1038/s41563-018-0257-4Structural transitions departing from the known phases of MoTe2 are induced by applying a vertical electric field to multilayers of this material. These distorted structures show distinct conducting states that can be used for resistive memories.

Published in: "Nature Materials".

Ultrahigh Photoresponsive Device Based on ReS2/Graphene Heterostructure

2018-12-02T00:34:16+00:00December 1st, 2018|Categories: Publications|Tags: , , , , , |

A photodetector based on a ReS2/graphene heterostructure is developed using the stacking method. The photodevice exhibits outstanding photoresponsivity (≈105 A W−1), detectivity (≈1013 Jones), and responsivity (<30 ms). The interface between ReS2 and graphene generates a high photocurrent because of the photogating effect under the applied gate voltage. Abstract Heterostructures that combine graphene and transition metal dichalcogenides, such as MoS2, MoTe2, and WS2, have attracted attention due to their high performances in optoelectronic devices compared to homogeneous systems. Here, a photodevice based on a hybrid van der Waals heterostructure of rhenium disulfide (ReS2) and graphene is fabricated using the stacking method. The device presents a remarkable ultrahigh photoresponsivity of 7 × 105 A W−1 and a detectivity of 1.9 × 1013 Jones, along with a fast response time of less than 30 ms. Tremendous photocurrents are generated in the heterostructure due to the direct bandgap, high quantum efficiency, and strong light absorption by the multilayer ReS2 and the high carrier mobility of graphene. The ReS2/graphene heterostructured device displays a high photocurrent under the applied gate voltages due to the photogating effect induced by the junction between graphene and ReS2. The ReS2/graphene heterostructure may find promising applications in future optoelectronic devices, providing a high sensitivity, flexibility, and transparency.

Published in: "Small".

Van der Waals Heterostructure Devices with Dynamically Controlled Conduction Polarity and Multifunctionality

2018-11-17T22:32:33+00:00November 17th, 2018|Categories: Publications|Tags: , , |

A new application of vdWHs to dynamically control and optimize the electronic and optoelectronic properties of 2D materials is demonstrated. The semivertical MoTe2/MoS2 structure allows for a desirable multifunctional integration of field effect transistorswith on/off ratio >107 and diode with rectification ratio >106. Moreover, the devices exhibit strong capability of suppressing the widely observed trap states–related negative photoresponse effect. Abstract Controlling the conduction behavior of 2D materials is an important prerequisite to achieve their electronic and optoelectronic applications. However, most of the reported approaches are aware of the shortcomings of inflexibility and complexity, which limits the possibility of multifunctional integration. Here, taking advantage of van der Waals heterostructure engineering, a simple method to achieve a dynamically controlled binary channel in a semivertical MoTe2/MoS2 field effect transistor is proposed. It is enabled by the high switchability between tunneling and thermal transports through simply changing the sign of voltage bias. In addition, the proposed system allows for multifunctional integration of transistor with on/off ratio >107 and diode with rectification ratio >106. Moreover, the devices show screen capability to negative photoresponse effect that is widely observed in ambipolar materials, hence improving the photodetection reliability and sensitivity. This study broadens the functionalities of van der Waals heterostructures and opens up more possibilities to realize multifunctional devices.

Published in: "Advanced Functional Materials".

Humidity‐Controlled Ultralow Power Layer‐by‐Layer Thinning, Nanopatterning and Bandgap Engineering of MoTe2

2018-11-17T22:32:03+00:00November 17th, 2018|Categories: Publications|Tags: |

A precision, laser‐assisted, humidity‐controlled, layer‐by‐layer thinning method in 2D MoTe2 films is presented. Field effect transistors fabricated from thinned layers exhibit an order of magnitude increase in on/off current, enhanced field‐effect mobility, and the fastest photoresponse for (visible) MoTe2 photodetectors reported to date. Localized band gap engineering is also performed, with sub‐200 nm spatial resolution, via the creation of lateral homojunctions. Abstract A highly effective laser thinning method is demonstrated to accurately control the thickness of MoTe2 layers. By utilizing the humidity present in the ambient atmosphere, multilayered MoTe2 films can be uniformly thinned all the way down to monolayer with layer‐by‐layer precision using an ultralow laser power density of 0.2 mW µm−2. Localized bandgap engineering is also performed in MoTe2, by creating regions with different bandgaps on the same film, enabling the formation of lateral homojunctions with sub‐200 nm spatial resolution. Field‐effect transistors fabricated from these thinned layers exhibit significantly improved electrical properties with an order of magnitude increase in on/off current ratios, along with enhancements in on‐current and field‐effect mobility values. Thinned devices also exhibit the fastest photoresponse (45 µs) for an MoTe2‐based visible photodetector reported to date, along with a high photoresponsivity. A highly sensitive monolayer MoTe2 photodetector is also reported. These results demonstrate the efficiency of the presented thinning approach in producing high‐quality MoTe2 films for electronic and optoelectronic applications.

Published in: "Advanced Functional Materials".

Coulomb scattering mechanism transition in 2D layered MoTe 2 : effect of high- κ passivation and Schottky barrier height

2018-11-16T12:35:23+00:00November 16th, 2018|Categories: Publications|Tags: |

Clean interface and low contact resistance are crucial requirements in two-dimensional (2D) materials to preserve their intrinsic carrier mobility. However, atomically thin 2D materials are sensitive to undesired Coulomb scatterers such as surface/interface adsorbates, metal-to-semiconductor Schottky barrier (SB), and ionic charges in the gate oxides, which often limits the understanding of the charge scattering mechanism in 2D electronic systems. Here, we present the effects of hafnium dioxide (HfO 2 ) high- κ passivation and SB height on the low-frequency (LF) noise characteristics of multilayer molybdenum ditelluride (MoTe 2 ) transistors. The passivated HfO 2 passivation layer significantly suppresses the surface reaction and enhances dielectric screening effect, resulting in an excess electron n -doping, zero hysteresis, and substantial improvement in carrier mobility. After the high- κ HfO 2 passivation, the obtained …

Published in: "Nanotechnology".

Van der Waals Heterostructure Devices with Dynamically Controlled Conduction Polarity and Multifunctionality

2018-11-16T04:33:51+00:00November 16th, 2018|Categories: Publications|Tags: , , |

A new application of vdWHs to dynamically control and optimize the electronic and optoelectronic properties of 2D materials is demonstrated. The semivertical MoTe2/MoS2 structure allows for a desirable multifunctional integration of field effect transistorswith on/off ratio >107 and diode with rectification ratio >106. Moreover, the devices exhibit strong capability of suppressing the widely observed trap states–related negative photoresponse effect. Abstract Controlling the conduction behavior of 2D materials is an important prerequisite to achieve their electronic and optoelectronic applications. However, most of the reported approaches are aware of the shortcomings of inflexibility and complexity, which limits the possibility of multifunctional integration. Here, taking advantage of van der Waals heterostructure engineering, a simple method to achieve a dynamically controlled binary channel in a semivertical MoTe2/MoS2 field effect transistor is proposed. It is enabled by the high switchability between tunneling and thermal transports through simply changing the sign of voltage bias. In addition, the proposed system allows for multifunctional integration of transistor with on/off ratio >107 and diode with rectification ratio >106. Moreover, the devices show screen capability to negative photoresponse effect that is widely observed in ambipolar materials, hence improving the photodetection reliability and sensitivity. This study broadens the functionalities of van der Waals heterostructures and opens up more possibilities to realize multifunctional devices.

Published in: "Advanced Functional Materials".

A semi-empirical integrated microring cavity approach for 2D material optical index identification at 1.55 {mu}m. (arXiv:1811.05323v1 [physics.app-ph])

2018-11-14T05:29:22+00:00November 14th, 2018|Categories: Publications|Tags: |

Atomically thin two-dimensional (2D) materials provide a wide range of basic building blocks with unique properties, making them ideal for heterogeneous integration with a mature chip platform for advances in optical communication technology. Control and understanding of the precise value of the optical index of these materials, however, is challenging, due to the small lateral flake dimension. Here we demonstrate a semi-empirical method to determine the index of a 2D material (nMoTe2 of 4.36+0.011i) near telecommunication-relevant wavelength by integrating few layers of MoTe2 onto a micro-ring resonator. The placement, control, and optical-property understanding of 2D materials with integrated photonics paves a way for further studies of active 2D material-based optoelectronics and circuits.

Published in: "arXiv Material Science".

Humidity‐Controlled Ultralow Power Layer‐by‐Layer Thinning, Nanopatterning and Bandgap Engineering of MoTe2

2018-11-13T10:32:52+00:00November 13th, 2018|Categories: Publications|Tags: |

A precision, laser‐assisted, humidity‐controlled, layer‐by‐layer thinning method in 2D MoTe2 films is presented. Field effect transistors fabricated from thinned layers exhibit an order of magnitude increase in on/off current, enhanced field‐effect mobility, and the fastest photoresponse for (visible) MoTe2 photodetectors reported to date. Localized band gap engineering is also performed, with sub‐200 nm spatial resolution, via the creation of lateral homojunctions. Abstract A highly effective laser thinning method is demonstrated to accurately control the thickness of MoTe2 layers. By utilizing the humidity present in the ambient atmosphere, multilayered MoTe2 films can be uniformly thinned all the way down to monolayer with layer‐by‐layer precision using an ultralow laser power density of 0.2 mW µm−2. Localized bandgap engineering is also performed in MoTe2, by creating regions with different bandgaps on the same film, enabling the formation of lateral homojunctions with sub‐200 nm spatial resolution. Field‐effect transistors fabricated from these thinned layers exhibit significantly improved electrical properties with an order of magnitude increase in on/off current ratios, along with enhancements in on‐current and field‐effect mobility values. Thinned devices also exhibit the fastest photoresponse (45 µs) for an MoTe2‐based visible photodetector reported to date, along with a high photoresponsivity. A highly sensitive monolayer MoTe2 photodetector is also reported. These results demonstrate the efficiency of the presented thinning approach in producing high‐quality MoTe2 films for electronic and optoelectronic applications.

Published in: "Advanced Functional Materials".

Nonvolatile and Programmable Photodoping in MoTe2 for Photoresist‐Free Complementary Electronic Devices

2018-11-10T22:34:20+00:00November 10th, 2018|Categories: Publications|Tags: , , |

A photoresist‐free p–n junction and inverter in the MoTe2 homostructure are achieved by spatially controlling the photodoping region in the MoTe2/BN heterostructure. The MoTe2 diode demonstrates an ideality factor of ≈1.13 with a current on/off ratio of ≈1.7 × 104, and the gain of the inverter reaches ≈98, illustrating its great potential in the application of 2D logic electronics. Abstract 2D transition‐metal dichalcogenide (TMD)‐based electronic devices have been extensively explored toward the post‐Moore era. Huge efforts have been devoted to modulating the doping profile of TMDs to achieve 2D p–n junctions and inverters, the fundamental units in logic circuits. Here, photoinduced nonvolatile and programmable electron doping in MoTe2 based on a heterostructure of MoTe2 and hexagonal boron nitride (BN) is reported. The electron transport property in the MoTe2 device can be precisely controlled by modulating the magnitude of the photodoping gate exerted on BN. Through tuning the polarity of the photodoping gate exerted on BN under illumination, such a doping effect in MoTe2 can be programmed with excellent repeatability and is retained for over 14 d in the absence of an external perturbation. By spatially controlling the photodoping region in MoTe2, a photoresist‐free p–n junction and inverter in the MoTe2 homostructure are achieved. The MoTe2 diode exhibits a near‐unity ideality factor of ≈1.13 with a rectification ratio of ≈1.7 × 104. Moreover, the gain of the MoTe2 inverter reaches ≈98, which is among the highest values for 2D‐material‐based homoinverters. These findings promise photodoping as an effective method to achieve

Published in: "Advanced Materials".

Nonvolatile and Programmable Photodoping in MoTe2 for Photoresist‐Free Complementary Electronic Devices

2018-11-07T08:35:35+00:00November 7th, 2018|Categories: Publications|Tags: , , |

A photoresist‐free p–n junction and inverter in the MoTe2 homostructure are achieved by spatially controlling the photodoping region in the MoTe2/BN heterostructure. The MoTe2 diode demonstrates an ideality factor of ≈1.13 with a current on/off ratio of ≈1.7 × 104, and the gain of the inverter reaches ≈98, illustrating its great potential in the application of 2D logic electronics. Abstract 2D transition‐metal dichalcogenide (TMD)‐based electronic devices have been extensively explored toward the post‐Moore era. Huge efforts have been devoted to modulating the doping profile of TMDs to achieve 2D p–n junctions and inverters, the fundamental units in logic circuits. Here, photoinduced nonvolatile and programmable electron doping in MoTe2 based on a heterostructure of MoTe2 and hexagonal boron nitride (BN) is reported. The electron transport property in the MoTe2 device can be precisely controlled by modulating the magnitude of the photodoping gate exerted on BN. Through tuning the polarity of the photodoping gate exerted on BN under illumination, such a doping effect in MoTe2 can be programmed with excellent repeatability and is retained for over 14 d in the absence of an external perturbation. By spatially controlling the photodoping region in MoTe2, a photoresist‐free p–n junction and inverter in the MoTe2 homostructure are achieved. The MoTe2 diode exhibits a near‐unity ideality factor of ≈1.13 with a rectification ratio of ≈1.7 × 104. Moreover, the gain of the MoTe2 inverter reaches ≈98, which is among the highest values for 2D‐material‐based homoinverters. These findings promise photodoping as an effective method to achieve

Published in: "Advanced Materials".

Electron Transport in Dirac and Weyl Semimetals. (arXiv:1809.03282v1 [cond-mat.mtrl-sci])

2018-09-11T02:29:19+00:00September 11th, 2018|Categories: Publications|Tags: |

Recently, the Dirac and Weyl semimetals have attracted extensive attention in condensed matter physics due to both the fundamental interest and the potential application of a new generation of electronic devices. Here we review the exotic electrical transport phenomena in Dirac and Weyl semimetals. Section 1 is a brief introduction to the topological semimetals (TSMs). In Section 2 and Section 3, the intriguing transport phenomena in Dirac semimetals (DSMs) and Weyl semimetals (WSMs) are reviewed, respectively. The most widely studied Cd3As2 and the TaAs family are selected as representatives to show the typical properties of DSMs and WSMs, respectively. Beyond these systems, the advances in other TSM materials, such as ZrTe5 and the MoTe2 family, are also introduced. In Section 4, we provide perspectives on the study of TSMs especially on the magnetotransport investigations.

Published in: "arXiv Material Science".

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