Type-II band-alignment in vertical transition metal-di-chalcogenide heterostructures for near infrared and visible light detection

In this work, group-6 and group-7 (ReSe<inf>2</inf>) transition metal-di-chalcogenide (TMD) heterostructures are studied systematically using density functional theory (DFT). Different combinations of ReSe<inf>2</inf> and group-6 TMDs are explored to identify the heterostructures with ‘type-II band-alignment’. ReSe2 monolayer is chosen as group-7 TMD because of its dynamic stability. Materials like MoS<inf>2</inf>, MoSe<inf>2</inf>, MoTe<inf>2</inf>, WS<inf>2</inf> and WSe<inf>2</inf> are chosen as group-6 TMDs. The heterostructures are evaluated in terms of metrics like; type of band-alignment, band-offsets, optical absorption and potential difference across the interface. ReSe<inf>2</inf>/MoS<inf>2</inf>, ReSe<inf>2</inf>/MoSe<inf>2</inf> and ReSe<inf>2</inf>/WS<inf>2</inf> heterostructures are identified as materials with ‘type-II band-alignment’ having bandgap values of 0.447 eV, 0.956 eV and 0.684 eV respectively. The identified ‘type-II heterostructures’ show a high absorption coefficient (∼40 × 10⁴ cm⁻¹) in visible-light region of the electromagnetic spectrum. Also, these ‘type-II heterostructures’ show a considerable potential drop across the interface (3.49 eV, for ReSe<inf>2</inf>/MoS<inf>2</inf>, heterostructure), which is important for efficient separation of photogenerated carriers into electrons and holes. This potential drop is crucial for limiting the recombination of photogenerated carriers. Furthermore, based on the performance metrics it is shown, among the studied heterostructures, ReSe<inf>2</inf>/MoS<inf>2</inf>, ReSe<inf>2</inf>/MoSe<inf>2</inf> and ReSe<inf>2</inf>/WS<inf>2</inf> heterostructures are suitable for light detecting applications in visible-light region of electromagnetic spectrum. Moreover, ReSe<inf>2</inf>/MoTe<inf>2</inf> and ReSe<inf>2</inf>/WSe<inf>2</inf> heterostructures show a ‘type-I band-alignment’.