Multilayer GaSe/InSe Heterointerface-Based Devices for Charge Transport and Optoelectronics

Interface interactions between two distinct layered materials of vertically stacked van der Waals (vdW) heterostructures play a vital role in the modulation of their electrical/optoelectronic properties. Meanwhile, intriguing properties, e.g., ultrafast charge transfer (Jin Nat Nanotechnol., 2018, 13, 994−1003) and moiré excitons (Tran et al Nature, 2019, 567, 71−75), have been discovered in strongly coupled heterobilayers composed of transition metal dichalcogenides; post-transition metal chalcogenides GaSe and InSe remain unexplored. Here, we use photoluminescence measurements and a scanning photoelectron microscope for electronic characterization of multilayer vertically stacked GaSe/InSe samples coupled with two-probe electrical measurements to reveal the carrier transport and optoelectronic properties at a strongly coupled GaSe/InSe vdW interface. A significant PL quenching and a shift of the valence band with respect to the Fermi level occurred at the heterojunction, evidencing the strong coupling of charge transfer between the GaSe and InSe layers. The band alignment at this heterointerface was determined as a type-II band alignment, similar to a weakly coupled system; however, charge transfer led to charge redistribution in the vicinity of the heterointerface, resulting in an interface dipole. Strong interface coupling also made the origin of the forward current different from that of the weakly coupled system; it is governed by interlayer recombination between the majority carriers rather than carrier injection over conduction band offsets. Moreover, tuning the band alignment via modulation of the majority carriers could further change the origin of the photocurrent. Our results not only present the first charge transport study of a strongly coupled multilayer GaSe/InSe system but also open up the way to further utilizing vdW interfaces in the applications of next-generation optoelectronics.