Two-step method enables controllable WS₂ epitaxy growth

In a study published in Journal of the American Chemical Society, a team led by Prof. Song Li from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences synthesized monolayer WS₂ lateral homojunctions via in situ domain engineering, and enabled controllable direct chemical vapor deposition (CVD) growth of these structures.

Two-dimensional (2D) transition metal dichalcogenides are ideal candidates to replace silicon-based semiconductors due to their exceptional electrical properties at atomic scales. However, device applications require heterogeneous field-effect modulation behaviors across low-dimensional units. Van der Waals interactions or lateral atomic bonding allow damage-free integration into homojunctions/heterojunctions, but direct epitaxy growth remains challenging due to strict atomic species constraints.

In this study, researchers first determined optimal intrinsic defect configurations through theoretical simulations. Then they employed a two-step CVD method to achieve the in situ modulation of defect structures at the domain level, yielding homojunctions with tailored defect architectures.

In the first step, two types of domains in hexagonal samples were created under equilibrium growth conditions. In the second step, in order to meet the device requirements, the atomic configurations of specific domains were in situ manipulated to engineer the band structures of homojunctions.

It is worth mentioning that to control the epitaxy growth process, researchers manipulated the precursor feeding rates of tungsten trioxide and sulfur to an equilibrium state, which enabled the growth rate of the S-zigzag edges to be equal to that of the W-zigzag edges.

The synthesized WS₂ homojunctions exhibited distinct field-effect characteristics while maintaining atomic lattice matching and customized band alignment at interfaces. Logic inverters based on these structures demonstrated rail-to-rail operation with a peak voltage gain of 12, dynamic delay of ~135 μs, and ultralow power consumption of 1.3 nW.

The study provides a new perspective on in-situ engineering of both defect configurations and distributions within atomic layers, and a more comprehensive understanding of 2D landscape.