Non-uniform Strain Distribution and Shape Evolution of monolayer MoSe2-WSe2 Lateral Heterojunction
Li-Syuan Lu (呂秝萱)1*, Dean Wang (王鼎)1, Chia-Chin Cheng (鄭嘉晉)2, Lian-Jong Li (李連忠)3, Wen-Hao Chang (張文豪)1
1Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
2Department of Material Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan
3Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
* presenting author:Li-Shuan Lu,
Lateral heterojunctions of two-dimensional transition metal dichalcogenides have attracted considerable attention recently since they can form atomically thin p-n junctions for applications in electronics and optoelectronics. In this work, we report on a one-step growth of monolayer MoSe2-WSe2 lateral heterojunctions by chemical vapor deposition using MoO2, WO3 and Se powders as source materials. Depending on the distance from the MoO2 precursor, the growth of inner MoSe2 undergoes different Mo:Se ratio conditions in different regions, resulting in either hexagonal or truncated triangular flakes. The longer sides of the truncated triangles can be either Mo-zigzag (Mo-zz) or Se-zz termination edges, depending on the region is grown under Mo-rich or Se-rich conditions. On the other hand, we found that the outer WSe2 are always outgrowing from the Se-zz edges of the inner MoSe2, indicating that the WSe2 are mostly grown under Se-rich conditions. The outer WSe2 thus displays a Se-rich shape evolution with the termination edges of the inner MoSe2. Photoluminescence (PL) mapping and Raman measurements show that the strain distribution in the WSe2 is non-uniform. Second harmonic generation (SHG) microscopy, on the other hand, reveals that the outgrowing WSe2 is single crystalline with the same orientation as the inner MoSe2. Based on the observed shape evolution and strain distribution in the outer WSe2, we propose a growth model to explain the termination dependent edge-epitaxial growth of MoSe2-WSe2 lateral heterojunctions.

Keywords: lateral heterojunctions, MoSe2-WSe2