Tuning Interlayer Exciton Emission with TMD Alloys in van der Waals Heterobilayers of Mo_0.5W_0.5Se₂ and Its Binary Counterparts

Semiconductor heterostructures have been the backbone of developments in electronic and optoelectronic devices. One class of structures of interest is the so-called type II band alignment, in which optically excited electrons and holes relax into different material layers. The unique properties observed in two-dimensional transition metal dichalcogenides and the possibility to engineer van der Waals heterostructures make them candidates for future high-tech devices. In these structures, electronic, optical, and magnetic properties can be tuned through the interlayer coupling, thereby opening avenues for developing new functional materials. We report the possibility of explicitly tuning the emission of interlayer exciton energies in the binary-ternary heterobilayer of Mo0.5W0.5Se2 with MoSe2 and WSe2. The respective interlayer energies of 1.516 eV and 1.490 eV were observed from low-temperature photoluminescence measurements for the MoSe2- and WSe2- based heterostructures, respectively. These interlayer emission energies are above those reported for MoSe2/WSe2 (similar or equal to 1.30-1.45 eV). Consequently, binary-ternary heterostructure systems offer an extended energy range and tailored emission energies not accessible with the binary counterparts. Moreover, even though Mo0.5W0.5Se2 and MoSe2 have almost similar optical gaps, their band offsets are different, resulting in charge transfer between the monolayers following the optical excitation. Thus, confirming TMDs alloys can be used to tune the band-offsets, which adds another design parameter for application-specific optoelectronic devices.