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Mixed-dimensional composite structures using 0D quantum dots (QDs) and 2D transition metal dichalcogenides (TMDs) materials are expected to attract great interest in optoelectronics due to potential to generate new optical properties. Here, we report on the unique optical characteristics of a devices with a mixed dimensional vertically stacked structures based on WSe2/CdSeS QDs monolayer/MoS2 (2D/0D/2D). Specifically, it exhibits an ambipolar photoresponse characteristic, with a negative photoresponse observed in the 400–600 nm wavelength range and a positive photoresponse appearing at 700 nm wavelength. It resulted the high negative responsivity of up to 52.22 mA/W under 400 nm, which is 163 times higher than that of the photodetector without CdSeS QDs. We also demonstrate the negative photoresponse which could be due to increased carrier collision probability and non-radiative recombination. Device modeling and simulation reveal that Auger recombination among the types of non-radiative recombination is the main cause of negative photocurrent generation. Consequently, we have discovered ambipolar photoresponse near a specific wavelength corresponding to the energy of quantum dots. Our study reveals interesting phenomenon in the mixed low-dimensional stacked structure and paves the way to exploit it for the development of innovative photodetection materials as well as for optoelectronic applications.

The characteristics of a flexible write-once-read-many-times (WORM) memory fabricated with monolayered 0-dimensional (0D) CdSe–ZnS quantum dots (QDs) layers sandwiched between two insulating 2-dimensional (2D) hexagonal boron nitride (hBN) multilayers were investigated by electrical measurement method. The hBN/QDs monolayer/hBN structure was fabricated in a vertical stacked structure using a technique which control the formation of the QDs monolayer. QDs monolayer was formed by electrostatic interaction between the negative charge group on the CdSe–ZnS QDs surface and the positive charge group on the hBN surface. The device has a WORM characteristic due to the presence of QDs in the current-voltage (I–V) measurement. When a bias is applied, carriers were initially trapped by tunneling due to the QDs and then a conductive filament was formed in the hBN, which were not detrapped and exhibit characteristics of write-once-read-many-times memory. The maximum ON/OFF ratio of the current for the devices was as large as 4 × 10, and the endurance was 5 × 104 cycles, and a retention time was larger than 1 × 105 s. In order to explain the carrier transport mechanism and conductive filament of the WORM memory device caused by QDs, it through various methods such as I–V fitting data, simulation, and conductive AFM. Unlike the conventional conductive filament mechanism, through random diffusion such as Ag filament, the Au/hBN/QD/hBN/ITO/PET structures implemented a consistent conductive filament using Au metal and QDs active layer.

We report on the synthesis of large-area molybdenum disulfide (MoS2) film on an insulating substrate by means of chemical vapor deposition. A single mixture of molybdenum hexacarbonyl (Mo(CO)6) and dimethyl disulfide (C2H6S2) was utilized as an organic liquid precursor for the synthesis of MoS2 film. Carbon impurities stemming from the dissociation of the organic precursor are effectively removed by water oxidation, and hydrogen gas, which is a by-product of the oxidation of carbon impurities, inhibits the formation of molybdenum oxides. The use of a liquid precursor assisted with water oxidation ensures high reproducibility and full-coverage of MoS2 film for large area, which is not typically achieved with solid precursors such as molybdenum oxide and sulfur powder. We believe that our approach will advance the synthesis of transition metal dichalcogenides.

Although hexagonal boron nitride (h-BN) is a good candidate for gate-insulating materials by minimizing interaction from substrate, further applications to electronic devices with available two-dimensional semiconductors continue to be limited by flake size. While monolayer h-BN has been synthesized on Pt and Cu foil using chemical vapour deposition (CVD), multilayer h-BN is still absent. Here we use Fe foil and synthesize large-area multilayer h-BN film by CVD with a borazine precursor. These films reveal strong cathodoluminescence and high mechanical strength (Young’s modulus: 1.16±0.1 TPa), reminiscent of formation of high-quality h-BN. The CVD-grown graphene on multilayer h-BN film yields a high carrier mobility of ~24,000 cm[superscript 2] V[superscript −1] s[superscript −1] at room temperature, higher than that (~13,000 [superscript 2] V[superscript −1] s[superscript −1]) with exfoliated h-BN. By placing additional h-BN on a SiO[subscript 2]/Si substrate for a MoS[subscript 2] (WSe[subscript 2]) field-effect transistor, the doping effect from gate oxide is minimized and furthermore the mobility is improved by four (150) times., Korea Institute of Science and Technology. Institutional Program, National Science Foundation (U.S.) (STC Center for Integrated Quantum Materials Grant DMR-1231319), Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies