WO-WS Vertical Bilayer Heterostructures with High Photoluminescence Quantum Yield.

Atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDCs) are attractive for applications in a wide range of optoelectronic devices, due to their tremendous interesting physical properties. However, the photoluminescence quantum yield (PLQY) of TMDCs has been found to be too low, due to abundant defects and strong many-body effect. Here, we present a direct physical vapor growth of WO-WS bilayer heterostructures, with WO monolayer domains attached on the surface of large-size WS monolayers. Optical characterizations revealed that the PLQY of the as-grown WO-WS heterostructures can reach up to 11.6%, which is 2 orders of magnitude higher than that of WS monolayers by the physical vapor deposition growth method (PVD-WS) and about 13-times higher than that of mechanical exfoliated WS (ME-WS) monolayers, representing the highest PLQY reported for direct growth TMDCs materials so far. The PL enhancement mechanism has been well investigated by time-resolved optical measurements. The fabrication of WO-WS heterostructures with ultrahigh PLQY provides an efficient approach for the development of highly efficient 2D integrated photonic applications.