Recent development in atomically thin layered materials has provided a new possibility for studying two-dimensional (2D) physics. Among them, the monolayer transition metal dichalcogenides (TMDs) with direct bandgaps in the near-infrared to the visible region and with unique electrical and mechanical properties have attracted great research interests and have shown the application potential in optoelectronics. Furthermore, the TMDs heterojunction not only can form the p-n junction as the basic building block for logic circuits, also can provide a new route for band engineering which is of scientific and technology important for exploring next generation electronics. However, the difficulty on precise spatial and geometry control during synthesis or preparation is still an obstacle for 2D materials to integrate into real circuit applications.

Herein, we demonstrate a simple spatially controlled process for synthesizing self-aligned monolayer lateral TMDs heterojunctions array in centimeter scale. The selective growth from metal pad can help on in-situ location and geometry control for forming the heterojunction devices without patterning process. Meanwhile, this etching-free growth method provides a clean and high quality lateral junction. Our WSe₂-MoS₂ p-n junction exhibits clear current rectification effect and electroluminescence (EL) from the interface under forward bias > 3 V. Detailed EL mechanism shall be discussed. Our self-aligned growth can be easy applied in large scale device fabrication or integrate into circuit design for achieving optoelectronic applications, and also provide a better platform for fundamental studies.