Recent Progress in Fabrication and Physical Properties of 2D TMDC-Based Multilayered Vertical Heterostructures

Two-dimensional (2D) vertical heterojunctions (HSs), which are usually fabricated by vertically stacking two layers of transition metal dichalcogenide (TMDC), have been intensively researched during the past years. However, it is still an enormous challenge to achieve controllable preparation of the TMDC trilayer or multilayered van der Waals (vdWs) HSs, which have important effects on physical properties and device performance. In this review, we will introduce fundamental features and various fabrication methods of diverse TMDC-based multilayered vdWs HSs. This review focuses on four fabrication methods of TMDC-based multilayered vdWs HSs, such as exfoliation, chemical vapor deposition (CVD), metal-organic chemical vapor deposition (MOCVD), and pulsed laser deposition (PLD). The latest progress in vdWs HS-related novel physical phenomena are summarized, including interlayer excitons, long photocarrier lifetimes, upconversion photoluminescence, and improved photoelectrochemical catalysis. At last, current challenges and prospects in this research field are provided.

Synthesis of transition metal dichalcogenide van der Waals heterostructures through chemical vapor deposition

Transition metal dichalcogenide (TMD) van der Waals (vdW) heterostructures show great potential in the exploration of novel physical phenomena and practical applications. Compared to the traditional mechanical stacking techniques, chemical vapor deposition (CVD) method exhibits more advantages in preparing TMD vdW heterostructures. CVD enables the large-scale production of high-quality materials with clean interfaces in the future. Herein, CVD methods for the synthesis of TMD vdW heterostructures are summarized. These methods are categorized in two major strategies, multi-step process and one-step process. The effects of various factors are demonstrated, including the temperature, nucleation, and precursors. Finally, the remaining challenges are discussed.

Controllable Epitaxial Growth of Large-Area MoS2 /WS2 Vertical Heterostructures by Confined-Space Chemical Vapor Deposition

The controllable large-area growth of single-crystal vertical heterostructures based on 2D transition metal dichalcogenides (TMDs) remains a challenge. Here, large-area vertical MoS₂ /WS₂ heterostructures are synthesized using single-step confined-space chemical vapor epitaxy. The heterostructures can evolve into two different kinds by switching the H₂ flow on and off: MoS₂ /WS₂ heterostructures with multiple WS₂ domains can be achieved without introducing the H₂ flow due to the numerous nucleation centers on the bottom MoS₂ monolayer during the transition stage between the MoS₂ and WS₂ monolayer growth. In contrast, isolated MoS₂ /WS₂ heterostructures with single WS₂ domain can be obtained with introducing the H₂ flow due to the reduced nucleation centers on the bottom MoS₂ monolayer arising from the hydrogen etching effect. Both the two kinds of the vertical MoS₂ /WS₂ heterostructures feature high quality. The photodetectors based on the isolated MoS₂ /WS₂ heterostructures exhibit a high responsivity of 68 mA W^-1 and a short response time of 35 ms. This single-step chemical vapor epitaxy can be used to synthesize vertical MoS₂ /WS₂ heterostructures with high production efficiency. The new epitaxial growth approach may open new pathways to fabricate large-area heterostructures made of different 2D TMDs monolayers of interest to electronics, optoelectronics, and other applications.

Recent progress in the CVD growth of 2D vertical heterostructures based on transition-metal dichalcogenides

This review summarizes recent advances in the controllable CVD growth of 2D TMDC vertical heterostructures under four different strategies.