Shape Evolution Induced by Edge Termination of Monolayer MoSe2-WSe2 Lateral Heterojunctions
Li-Syuan Lu (呂秝萱)1*, Dean Wang (王鼎)1, Ming Hao Lee (李明浩)2, Ming Wen Chu (朱明文)2, Lian-Jong Li (李連忠)3, Wen-Hao Chang (張文豪)1
1Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
2Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
3Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
* presenting author:Li-Syuan Lu,
Monolayer lateral heterojunctions (HJs) formed by two distinct transition metal dichalcogenides have been considered as a new class of atomically thin p-n junctions for applications in electronics and optoelectronics. In this work, we report on the growth of monolayer MoSe2 -WSe2 lateral HJs by hot-wall chemical vapor deposition through a one-step growth method using MoO2, WO3 and Se powders as source precursors. Depending on the distance from the sources, the shape of inner MoSe2evolves from truncated triangle at the upstream to hexagonal and eventually return to triangle at the downstream, leading to a unique shape evolution in the outer WSe2. Second harmonic generation microscopy reveals that the outgrowing WSe2 is single crystalline with the same orientation with the inner MoSe2. High-angle-annular-dark-field scanning transmission electron microscopy (HAADF STEM) analysis of the edge terminations suggests that the inner MoSe2 growth evolves form Se-rich condition at the upstream to Mo-rich condition at the downstream, while the WSe2 growth is all the way under W-rich condition. The outer WSe2 thus always outgrows from the Mo-zigzag termination edges, resulting in distinct shapes in the outer WSe2 depending on the inner MoSe2 shapes. Based on the observed shape evolution, we propose a growth model to explain the termination dependent edge-epitaxial growth of MoSe2-WSe2 lateral HJs.

Keywords: MoSe2, WSe2, Heterojunctions