Direct Bilayer Growth: a New Growth Fundamental for Novel WSe2 Homo-junction and Bilayer WSe2 Growth
Homo-junction and multi-layer structures of transition metal chalcogenide (TMD) materials provide great flexibility for band-structure engineering and photoelectric devices designing. However, the growth understanding of the van der Waals epitaxy limits the advances of this heterostructure. Here, we employ chemical vapor deposition (CVD) growth strategy to synthesize a novel WSe2 homo-junction samples with a triangular monolayer in the center and three AA stacking bilayer flakes connected to the vertexes of the monolayer. Emitted photon energy from the bilayer near the junction shows an energy blue shift up to 24 meV compared with bare bilayer WSe2, confirming the charge transferring effect from monolayer to bilayer WSe2. Further growth studies reveal the shape evolution from WSe2 homo-junction to bilayer. The whole homo-junction formation and evolution process cannot be explained by the traditional layer-by-layer growth mechanism. Instead, a direct bilayer growth approach is proposed to explain the bilayer formation and evolution at the vertexes of the bottom layer of WSe2. These findings suggest the bilayer TMDs growth could be more complex than our understanding. This work deep the growth understanding of van der Waals epitaxy and thus is valuable for guiding the fabrication of novel homo-junction for both fundamental science and optoelectronic applications.