Robust Growth of 2D Transition Metal Dichalcogenide Vertical Heterostructures via Ammonium-Assisted CVD Strategy

Abstract

Two dimension (2D) transition metal dichalcogenides (TMD) heterostructures have opened unparalleled prospects for next-generation electronic and optoelectronic applications due to their atomic-scale thickness and distinct physical properties. The chemical vapor deposition (CVD) method is the most feasible approach to prepare 2D TMD heterostructures. However, the synthesis of 2D vertical heterostructures faces competition between in-plane and out-of-plane growth, which makes it difficult to precisely control the growth of vertical heterostructures. Here, a universal and controllable strategy is reported to grow various 2D TMD vertical heterostructures through an ammonium-assisted CVD process. The ammonium-assisted strategy shows excellent controllability and operational simplicity to prevent interlayer diffusion/alloying and thermal decomposition of the existed TMD templates. Ab initio simulations demonstrate that the reaction between NH₄Cl and MoS₂ leads to the formation of MoS₃ clusters, promoting the nucleation and growth of 2D MoS₂ on existed 2D WS₂ layer, thereby leading to the growth of vertical heterostructure. The resulting 2D WSe₂/WS₂ vertical heterostructure photodetectors demonstrate an outstanding optoelectronic performance, which are comparable to the performances of photodetectors fabricated from mechanically exfoliated and stacked vertical heterostructures. The ammonium-assisted strategy for robust growth of high-quality vertical van der Waals heterostructures will facilitate fundamental physics investigations and device applications in electronics and optoelectronics.

Keywords: chemical vapor deposition; optoelectronics; transition metal dichalcogenides; van der Waals heterostructures.