molybdenum diselenide/tungsten diselenide (MoSe 2 /WSe 2 ), have been studied due to tunneling-mediated recombination and unconventional transport behaviors. [4,5] Main advantage of vdW heterostructures is that any of 2D materials can be arbitrarily stacked with weak vdW force without consideration of lattice mismatch, contrarily to the epitaxial growth in the conventional semiconductors. It has been well known that band structures of the TMDs depend on their thicknesses, e.g., lager band gap for thinner TMDs due to quantum confinement effect and homojunctions between the same TMDs with different thicknesses have unique band offsets. [6,7] Nevertheless, study on these homo-junctions are lacking. Just a few papers reported an electron transport in conduction band offset of the MoS 2 homojunctions. [8,9] However, MoS 2 shows only n-type electrical transport regardless of the thickness.Among the TMDs, WSe 2 has high tunability of charge carriers and high room temperature quantum yield, which is beneficial for optoelectronic applications. [10][11][12] It indicates that polarity of the intrinsically ambipolar WSe 2 can be easily modulated. Especially, as the thickness of WSe 2 increases, it shows carrier type transition from p-type to n-type due to a large shift of valence band and reduced contact barrier for hole. [13] Transition metal dichalcogenides (TMDs), one of the 2D semiconductors, such as molybdenum disulfide (MoS 2 ) and tungsten diselenide (WSe 2 ), exhibit novel physical and electronic properties that are useful for electronic and optoelectronic applications. Recently, the van der Waals heterostructures consisting of different 2D materials have been studied actively as various combinations of 2D materials can be fabricated with exceptional performance and physical properties. Nevertheless, study on homo-junction of the same TMDs layers is lacking. Here, it is demonstrated that a vertical homojunction consisting of two WSe 2 flakes with different thicknesses shows anti-ambipolar transport behavior due to a thickness-induced band offset at the interface. Photo-response current is generated by tunneling-mediated interlayer recombination at the WSe 2 homo-junction. The band structures of homo-junctions of TMDs can be engineered by the thickness, which would be beneficial for understanding transport at the interfaces of 2D materials and developing the next generation devices.

A photoluminescence mapping image of monolayer (1L) MoS2 clearly shows the difference in PL intensity at the boundary between bare SiO2 and plasma-treated SiO2 (3 min).

Transition metal dichalcogenides (TMDs) are promising candidates for semiconductor industry owing to their superior electrical properties. Their surface oxidation is of interest because their electrical properties can be easily modulated...

2D materials with atomic-scale thickness have attracted immense interest owing to their intriguing properties, which can be useful for electronic devices. As ultrathin 2D materials are highly vulnerable to external conditions, passivation of 2D materials is required to maintain the stability of 2D electronic devices. However, 2D channels are embedded in passivation layers, making the formation of suitable contacts in passivated 2D devices challenging. Here, a novel method for fabricating irreversible conductive filament (ICF) contacts on a 2D channel passivated by hexagonal boron nitride (hBN) layers is demonstrated. Defective paths are formed in the top hBN layer of hBNencapsulated graphene (or MoS 2 ) using oxygen-plasma treatment, along which ICFs are fabricated by applying repetitive bias. ICF contacts formed in the combined paths of migrated metal atoms and vacancies are stable during device operation, which is in contrast with that the filaments in hBN memristors are reversible. Field-effect transistors with ICF contacts exhibit a low contact resistance and high stability. This study shows a new contact method, which has great potential for high-performance 2D electronics devices.

In article 2003567, Chul‐Ho Lee, Gwan‐Hyoung Lee, and co‐workers report the development of a novel light‐emitting field‐effect transistor (LEFET) based on a van der Waals heterostructure. Multiple modes of operation are achieved by controlling the injection of holes and electrons in the graphene–WSe2 contacts. Effective recombination of excitons in the 2D layer enables high external quantum efficiency in the LEFET, which will play an important role in future optoelectronic circuits.