Hybrid structures of two-dimensional (2D) materials and quantum dots (QDs) are particularly interesting in the field of nanoscale optoelectronic devices because QDs are efficient light absorbers and can inject photocarriers into thin layers of 2D transition-metal dichalcogenides, which have high carrier mobility. In this study, we present a heterostructure that consists of a monolayer of tungsten diselenide (ML WSe) covered by nitrogen-doped graphene QDs (N-GQDs). The improved photoluminescence of ML WSe is attributed to the dominant neutral exciton emission caused by the n-doping effect. Owing to strong light absorption and charge transfer from N-GQDs to ML WSe, N-GQD-covered ML WSe showed up to 480% higher photoresponsivity than that of a pristine ML WSe photodetector. The hybrid photodetector exhibits good environmental stability, with 46% performance retention after 30 days under ambient conditions. The photogating effect also plays a key role in the improvement of hybrid photodetector performance. On applying the back-gate voltage modulation, the hybrid photodetector shows a responsivity of 2578 A W, which is much higher than that of the ML WSe-based device.

Monolayer (1L) transition metal dichalcogenides (TMDCs) are promising materials for nanoscale optoelectronic devices because of their direct band gap and wide absorption range (ultraviolet to infrared). However, 1L-TMDCs cannot be easily utilized for practical optoelectronic device applications (e.g., photodetectors, solar cells, and light-emitting diodes) because of their extremely low optical quantum yields (QYs). In this investigation, a high-gain 1L-MoS photodetector was successfully realized, based on the surface plasmon (SP) of the Ag nanowire (NW) network. Through systematic optical characterization of the hybrid structure consisting of a 1L-MoS and the Ag NW network, it was determined that a strong SP and strain relaxation effect influenced a greatly enhanced optical QY. The photoluminescence (PL) emission was drastically increased by a factor of 560, and the main peak was shifted to the neutral exciton of 1L-MoS. Consequently, the overall photocurrent of the hybrid 1L-MoS photodetector was observed to be 250 times better than that of the pristine 1L-MoS photodetector. In addition, the photoresponsivity and photodetectivity of the hybrid photodetector were effectively improved by a factor of ∼1000. This study provides a new approach for realizing highly efficient optoelectronic devices based on TMDCs.

We study the electronic and optoelectronic properties of a broken-gap heterojunction composed of SnSe2 and MoTe2 with gate-controlled junction modes. Owing to the interband tunneling current, our device can act as an Esaki diode and a backward diode with a peak-to-valley current ratio approaching 5.7 at room temperature. Furthermore, under an 811 nm laser irradiation the heterostructure exhibits a photodetectivity of up to 7.5 × 1012 Jones. In addition, to harness the electrostatic gate bias, V oc can be tuned from negative to positive by switching from the accumulation mode to the depletion mode of the heterojunction. Additionally, a photovoltaic effect with a fill factor exceeding 41% was observed, which highlights the significant potential for optoelectronic applications. This study not only demonstrates high-performance multifunctional optoelectronics based on the SnSe2/MoTe2 heterostructure but also provides a comprehensive understanding of broken-band alignment and its applications.

Various functional devices including p-n forward, backward, and Zener diodes are realized with a van der Waals heterostructure that are composed of molybdenum disulfide (MoS2) and molybdenum ditelluride (MoTe2) by changing the thickness of the MoTe2 layer and common gate bias. In addition, the available negative differential transconductance of the heterostructure is utilized to fabricate a many-valued logic device that exhibits three different logic states (i.e., a ternary inverter). Furthermore, the multivalued logic device can be transformed into a binary inverter using laser irradiation. This work provides a comprehensive understanding of the device fabrication and electronic-device design utilizing thickness control.

We present a novel metal-insulator-semiconductor (MIS) diode consisting of graphene, hexagonal BN, and monolayer MoS2 for application in ultrathin nanoelectronics. The MIS heterojunction structure was fabricated by vertically stacking layered materials using a simple wet chemical transfer method. The stacking of each layer was confirmed by confocal scanning Raman spectroscopy and device performance was evaluated using current versus voltage (I-V) and photocurrent measurements. We clearly observed better current rectification and much higher current flow in the MIS diode than in the p-n junction and the metal-semiconductor diodes made of layered materials. The I-V characteristic curve of the MIS diode indicates that current flows mainly across interfaces as a result of carrier tunneling. Moreover, we observed considerably high photocurrent from the MIS diode under visible light illumination.

We propose a semiconductor-insulator-semiconductor (SIS) heterojunction diode consisting of monolayer (1-L) MoS2, hexagonal boron nitride (h-BN), and epitaxial p-GaN that can be applied to high-performance nanoscale optoelectronics. The layered materials of 1-L MoS2 and h-BN, grown by chemical vapor deposition, were vertically stacked by a wet-transfer method on a p-GaN layer. The final structure was verified by confocal photoluminescence and Raman spectroscopy. Current-voltage (I-V) measurements were conducted to compare the device performance with that of a more classical p-n structure. In both structures (the p-n and SIS heterojunction diode), clear current-rectifying characteristics were observed. In particular, a current and threshold voltage were obtained for the SIS structure that was higher compared to that of the p-n structure. This indicated that tunneling is the predominant carrier transport mechanism. In addition, the photoresponse of the SIS structure induced by the illumination of visible light was observed by photocurrent measurements.

Two-dimensional transition-metal dichalcogenides (TMDCs) are notable materials owing to their flexibility, transparency, and appropriate bandgaps.

High-quality and large-area molybdenum disulfide (MoS ) thin film is highly desirable for applications in large-area electronics. However, there remains a challenge in attaining MoS film of reasonable crystallinity due to the absence of appropriate choice and control of precursors, as well as choice of suitable growth substrates. Herein, a novel and facile route is reported for synthesizing few-layered MoS film with new precursors via chemical vapor deposition. Prior to growth, an aqueous solution of sodium molybdate as the molybdenum precursor is spun onto the growth substrate and dimethyl disulfide as the liquid sulfur precursor is supplied with a bubbling system during growth. To supplement the limiting effect of Mo (sodium molybdate), a supplementary Mo is supplied by dissolving molybdenum hexacarbonyl (Mo(CO) ) in the liquid sulfur precursor delivered by the bubbler. By precisely controlling the amounts of precursors and hydrogen flow, full coverage of MoS film is readily achievable in 20 min. Large-area MoS field effect transistors (FETs) fabricated with a conventional photolithography have a carrier mobility as high as 18.9 cm V s , which is the highest reported for bottom-gated MoS -FETs fabricated via photolithography with an on/off ratio of ≈10 at room temperature.