Studies of Band Alignment in WS2/MoS2/Al2O3 Heterostructures using Kelvin Probe Force Microscopy

Two-dimensional (2D) crystals can be assembled into van der Waals (vdW) heterostructures by mechanical exfoliation or chemical vapor deposition. Charge transport and recombination processes are determined by the band alignment in the heterostructures. Therefore, investigation of the band alignment is a crucial step toward the applications of the 2D vdW heterostructures. In this work, we fabricated WS2/MoS2 heterostructures on single crystal Al2O3 wafers, using sulfurization of pre-deposited transition metal layers. The surface potential of the sample in dark and light was measured using Kelvin probe force microscopy, which allowed us to suggest the band diagrams of the vdW heterostructures. The measured Raman spectra of the heterostructures supported the proposed band alignment, considering the electronic interaction at the interface and the interlayer screening effects.