Direct formation of interlayer excitons in MoSSe/WSSe van der Waals heterobilayer.

In respect to the van der Waals structures composed of two-dimensional transition metal dichalcogenides, the interlayer excitonic physics plays a determinative role in the exciting new phenomena and applications in such as photonics, optoelectronics and valleytronics. In this work, beyond the well-accepted, conventional indirect two-step process, we proved that the large interlayer polarization can cause the direct formation of interlayer excitons in MoSSe/WSSe. In MoSSe/WSSe, the interlayer exciton with a sizable oscillator strength is located at 1.49 eV, well below the characteristic intralayer excitons, with a significantly reduced exciton binding energy of 0.28 eV and an improved exciton lifetime of 2.25 ns.