Promoting Interlayer Exciton in Janus/Transition Metal Dichalcogenide Heterostructures by Annealing

Recently discovered two-dimensional (2D) Janus monolayers are one of the members of 2D excitonic transition metal dichalcogenide (TMD) semiconductors. Unlike classical 2D TMDs, a two-faced atomic arrangement in the unit cell not only breaks the mirror symmetry but also induces a built-in polarization field. In return, interfacing 2D Janus with TMDs creates unique directions to manipulate interlayer excitons by engineering how the polarization direction or magnitude affects the neighboring 2D layers. Here, we report on interlayer excitonic properties of 2D heterobilayers involving Janus TMDs. The results first establish necessary ultrahigh vacuum annealing and cleaning steps in Janus/classical TMD bilayers with type-II band alignment to engineer the interlayer distance and interaction strength and to sustain interlayer excitons. Building on this, further studies change the polarization direction in four different bilayer configurations to engineer different polarization architectures. The results show that the polarization direction plays a significant role in determining the photoexcited carrier recombination and interlayer excitonic characteristics at the 2D interface. Overall, the study establishes the role of the polarization strength and direction in 2D bilayers involving 2D Janus TMDs and offers ways to engineer the interlayer exciton properties.