We investigate the photoresponse in the heterostructure device by a scanning photocurrent microscope (SPCM). Under sub-WS2 bandgap (780 nm) excitation, we find a photocurrent with unchanged polarity at the heterostructure region and detect only a weak signal at the electrode edges (Figure ), presumably originating from the hot carriers generated in graphene. This is detailed further in the extracted photocurrent line profile (Figure ), where the normalized photocurrent intensity at the heterostructure center is one order of magnitude higher than that at the electrodes.