Two-dimensional (2D) semiconductors hold promises for electronic and optoelectronic applications due to their outstanding electrical and optical properties. Despite a short research history, a wide range of ‘proof-of-concept’ devices based on 2D materials have been demonstrated, highlighting their impact in advanced technology. Here we review the unique properties 2D semiconducting materials and their applications in terms of electronic and optoelectronic devices. We summarize all the engineering issues in 2D devices, including material quality, dielectric, and contacts. We also discuss recent advances of 2D semiconductor devices in electronic and optoelectronic applications. This review would help to understand superior performance and multifunctions of 2D semiconductor devices and guide us toward new device applications of 2D semiconductors.

Monolayer transition metal dichalcogenides (TMDs) are promising for optoelectronics because of their high optical quantum yield and strong light-matter interaction. In particular, the van der Waals (vdW) heterostructures consisting of monolayer TMDs sandwiched by large gap hexagonal boron nitride have shown great potential for novel optoelectronic devices. However, a complicated stacking process limits scalability and practical applications. Furthermore, even though lots of efforts, such as fabrication of vdW heterointerfaces, modification of the surface, and structural phase transition, have been devoted to preserve or modulate the properties of TMDs, high environmental sensitivity and damage-prone characteristics of TMDs make it difficult to achieve a controllable technique for surface/interface engineering. Here, we demonstrate a novel way to fabricate multiple two-dimensional (2D) vdW heterostructures consisting of alternately stacked MoS2 and MoO x with enhanced photoluminescence (PL). We directly oxidized multilayer MoS2 to a MoO x /1 L-MoS2 heterostructure with atomic layer precision through a customized oxygen plasma system. The monolayer MoS2 covered by MoO x showed an enhanced PL intensity 3.2 and 6.5 times higher in average than the as-exfoliated 1 L- and 2 L-MoS2 because of preserved crystallinity and compensated dedoping by MoO x . By using layer-by-layer oxidation and transfer processes, we fabricated the heterostructures of MoO x /MoS2/MoO x /MoS2, where the MoS2 monolayers are separated by MoO x . The heterostructures showed the multiplied PL intensity as the number of embedded MoS2 layers increases because of suppression of the nonradiative trion formation and interlayer decoupling between stacked MoS2 layers. Our work shows a novel way toward the fabrication of 2D material-based multiple vdW heterostructures and our layer-by-layer oxidation process is beneficial for the fabrication of high performance 2D optoelectronic devices.

Covalent functionalization of the surface is more crucial in 2D materials than in conventional bulk materials because of their atomic thinness, large surface-to-volume ratio, and uniform surface chemical potential. Because...

Quantum wells (QWs), enabling effective exciton confinement and strong light-matter interaction, form an essential building block for quantum optoelectronics. For two-dimensional (2D) semiconductors, however, constructing the QWs is still challenging because suitable materials and fabrication techniques are lacking for bandgap engineering and indirect bandgap transitions occur at the multilayer. Here, we demonstrate an unexplored approach to fabricate atomic–layer–confined multiple QWs (MQWs) via monolithic bandgap engineering of transition metal dichalcogenides and van der Waals stacking. The WOX/WSe2 hetero-bilayer formed by monolithic oxidation of the WSe2 bilayer exhibited the type I band alignment, facilitating as a building block for MQWs. A superlinear enhancement of photoluminescence with increasing the number of QWs was achieved. Furthermore, quantum-confined radiative recombination in MQWs was verified by a large exciton binding energy of 193 meV and a short exciton lifetime of 170 ps. This work paves the way toward monolithic integration of band-engineered heterostructures for 2D quantum optoelectronics.

Defects in hexagonal boron nitride (hBN) have attracted much attention since they are effectively used for nanoelectronics, such as single-photon emitters or memristors. The method for generating and controlling hBN defects is important because the defects are critical factors determining the optical and electrical properties of hBN. Here, we demonstrate the modulation of optical and electrical properties of hBN by defects generated via mild oxygen plasma treatment. The photoluminescence peaks related to defects were observed at a broad range (∼3.8 eV), and the current of plasma-treated hBN flow at the lower threshold voltage compared to the as-exfoliated hBN due to the formation of defect paths inside the hBN structure. We also demonstrate that the bandgap structure of hBN can be tuned by the oxygen plasma treatment. Our findings are useful for the stable and reliable fabrication of two-dimensional electronic devices using hBN in the future.