Two-dimensional (2D)-material-based photodetectors have recently received great attention due to their potential as ultrathin and ultra-highly integrated devices. In this study, we demonstrated the application of MoTe2 as electrode material for photodetectors. An all-2D photodetector based on WS2 and MoTe2 is fabricated. Owing to the large Schottky barrier formed between WS2 and MoTe2, the avalanche effect can be realized because a large electrical field can be applied across the MoTe2–WS2–MoTe2 junctions before breakdown. Additionally, because of the existence of Schottky barrier, the dark current of device is greatly reduced. As a result, we achieved the enhanced performance of the ultrathin all-2D photodetector, with a photoresponsivity of 6.02 AW-1, an external quantum efficiency of 1406%, an avalanche gain of 587, and a low dark current of 93 pA in the broadband spectrum range from visible-to-NIR wavelengths.
Terahertz (THz) waves, referring to electromagnetic waves with frequency range from 0.1 THz to 10 THz, have many novel and unique properties for a wide range of applications from security to medicine. However, it is relatively difficult to study the physical and chemical processes within this band due to limitation of sensitive terahertz detectors. As one of transition group metal oxides, two-dimensional van der Waals α-MoO3 crystal has relatively high carrier mobility and strong phonon polaritons effects. The relatively weak van der Waals forces between adjacent layers allow various atoms to easily enter into the crystal and interact with the lattice to produce defect states, enabling excellent optoelectronic conversion characteristics. In this study, we fabricate terahertz detectors based on hydrogen atom-intercalated α-MoO3 two-dimensional crystal integrated with log-periodic antenna, which operate from 0.25 THz to 0.37 THz with a maximum optical responsivity of 0.04 V/W.
Hybrid system composed of metal nanoparticles and two-dimensional transition metal dichalcogenides (TMDs) is important for studying the light-matter interaction at the nanoscale. In particular, the 2D excitons are very sensitive to external stimulus, allowing their active control via temperature scanning, gating, and optical excitation. In comparison with other active tuning strategies, chemical treatment is another effective method.
In this study, we realize tuning of the resonance coupling, through a chemical approach, in heterostructure composed of an individual gold nanorod integrated with monolayer WS2 flake. Treating the heterostructure with an organic superacid: bis(trifluoromethane)sulfonimide (TFSI), the photoluminescence intensity can be enhanced by 7 times. The coupled system has enhanced energy splitting about 50 meV. The chemical treatment based on the TFSI solution provides a new approach for tuning the resonance coupling effect.
In this work, the method of electrostatic doping is used to achieve the PL enhancement of large scale MoS2 grown by chemical vapor deposition (CVD) method. It has been found that the release of strain in the as-grown monolayers by the transfer process is essential for TMDCs PL enhancement. To ensure the low contamination level on the 2D materials, a dry-transfer technique based on polydimethylsiloxane (PDMS) was utilized to transfer monolayer MoS2. We found that the peak PL intensity of CVD-grown MoS2 showing an enhancement up to 200% by adding both positive and negative back-gate voltage (Vg). Compared with the chemical treatment method, electrostatic doping can realize the controllable process of PL, that is, the PL intensity is gradually tuned by the gate voltage. In addition, covering the sample with PMMA (polymethyl methacrylate) can isolate the influences of the external environment on the sample, which can improve the stability of the sample and enable more stable measurements.
KEYWORDS: Polaritons, Phonons, Nanoantennas, Photon polarization, Free space optics, Near field optics, Dispersion, Near field scanning optical microscopy, Free space, Boron
In this study, by using numerical simulations and scanning near-field optical microscopy, we investigate the excitation of HPhPs in MoO3 with plasmonic nanoantennas. We find that the excitation efficiency is strongly dependent on the antenna length and orientation. By changing the size, shape and direction of the metal antenna, the excitation of the phonon Polariton mode can be controlled.
This Conference Presentation, “Electromagnetic field manipulations in two-dimensional polaritonic crystals,” was recorded for the Photonics Asia 2020 Digital Forum.
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