Lateral heterostructures and one-dimensional interfaces in 2D transition metal dichalcogenides

Abstract

The growth and exfoliation of two-dimensional (2D) materials have led to the creation of edges and novel interfacial states at the juncture between crystals with different composition or phases. These hybrid heterostructures (HSs) can be built as vertical van der Waals stacks, resulting in a 2D interface, or as stitched adjacent monolayer crystals, resulting in one-dimensional (1D) interfaces. Although most attention has been focused on vertical HSs, increasing theoretical and experimental interest in 1D interfaces is evident. In-plane interfacial states between different 2D materials inherit properties from both crystals, giving rise to robust states with unique 1D non-parabolic dispersion and strong spinorbit effects. With such unique characteristics, these states provide an exciting platform for realizing 1D physics. Here, we review and discuss advances in 1D heterojunctions, with emphasis on theoretical approaches for describing those between semiconducting transition metal dichalcogenides M X 2 (with M =Mo, W and X= S, Se, Te), and how the interfacial states can be characterized and utilized. We also address how the interfaces depend on edge geometries (such as zigzag and armchair) or strain, as lattice parameters differ across the interface, and how these features affect excitonic/optical response. This review is intended to serve as a resource for promoting theoretical and experimental studies in this rapidly evolving field.

Bandgap engineering of two-dimensional semiconductor materials

“…The fabrication of seamless lateral heterojunctions has been pursued over the past few years as a path toward monolayer diodes and transistors, see refs. [231][232][233][234] . for reviews on their synthesis, optoelectronic properties, and device applications.…”

“…Strain engineering in such monolayer lateral junctions has been proven a challenging task, but it would allow for control of the alignment between energy bands of the materials in the heterojunction. Theoretical predictions also suggest that the band structure modification due to tensile strain across a monolayer MoS 2 /WS 2 lateral heterojuction would lead to charge carrier confinement at the interface, thus forming a one-dimensional channel that brings prospects for applications in high-electronmobility transistors and low-power switching devices 230,231,233 .…”

Edges and boundaries of transition metal dichalcogenides

“…Continuing with interfaces, in recent years, two-dimensional lateral junctions have attracted a lot of attention, as e↵ective growth techniques enable heterojunctions with sharp interfaces between di↵erent materials to be grown. In-plane p-n diodes and inplane field e↵ect transistors have been constructed [22][23][24][25][26].…”

“…Lateral structures grown from two-dimensional (2D) materials arouse growing scientific attention, because of their potential to open a route towards truly 2D electronics. In-plane p-n junctions and barrierless Schottky contacts between 2D compounds provide the basic building blocks of 2D electronic devices [26,122,123]. Lateral heterojunctions between a variety of 2D semiconductors are realized since chemical vapor deposition techniques have enabled the growth of sharp one-dimensional (1D) interfaces between di↵erent 2D materials.…”

“…The compounds with M = Mo, W, and X = S, Se, have attracted most attention, as they are direct band-gap semiconductors with potential applications in optoelectronics, photovoltaics, and photocatalysis [4,129,130]. Not surprisingly then, so far the focus has been mainly on junctions made from these materials, their band alignments and interface transport properties [26,[122][123][124][125][126][127][128].…”