Fig. 1: Band alignment and ultrafast charge transfer in TMD vdW heterostructures.
From: Interlayer exciton formation, relaxation, and transport in TMD van der Waals heterostructures
a Schematic illustration of the side-view structure (top) and the type-II band alignment (bottom) of a TMD vdW heterobilayer. e/h: electron/hole; ΔCB: conduction band offset of the constituent monolayers; ΔVB: valence band offset of the constituent monolayers; Eg: band gap of the heterobilayer. b Calculated band alignments of various TMD monolayers12. The bar and line-point plots represent the CBM (red color) and VBM (blue color) values obtained from PBE and HSE06 calculations, respectively. The positions of CBM and VBM on the Brillouin zone are shown in the figure. c Plot of the calculated band gaps (Eg) and the experimental PL energies of the interlayer excitons versus various TMD vdW heterostructures with a type-II band alignment. The calculated Eg values (circles) are obtained from references9,10,12,13,14. The experimental PL energies of the interlayer excitons (stars in the pink region) are obtained from references17,21,22,23,25,27,28,29,33,42,43,44,45,49,87,90,91,92,93,94,95,96,97,98,99,100,101,102,103, most of which overlap in the region from ~1.3 to ~1.5 eV. d Band alignment of a MoS2/WS2 heterobilayer57. The hole transfers from the VBM of MoS2 to that of WS2 after optically pumping the MoS2 A-exciton. e Twist-angle independent charge transfer dynamics (τ < 100 fs) obtained by selectively probing the WS2 A-exciton of the MoS2/WS2 heterobilayer57. f, g Schematic illustration of the phonon scattering-mediated interlayer electron transfer process in the energy (f) and momentum (g) spaces40. LA (A1′) represents the longitudinal acoustic phonons. h Schematic illustration of the ultrafast electron scattering from K to M, M/2, and Q valleys within 70 fs (black arrows) in a MoS2/WS2 heterobilayer and the subsequent electron scattering from M/2 and M back to K′ and Q′ valleys in the other layer within 400 fs (dashed arrows), as evidenced by TR-ARPES71. b Reprinted with permission from ref. 12 [American Physical Society]. d, e Reprinted with permission from ref. 57 [American Chemical Society]. f, g Reprinted with permission from ref. 40 [American Physical Society]. h Reprinted with permission from ref. 71 [American Physical Society]
