(color online) (a) Schematic of vertical WSe₂/MoS₂ heterojunction; (b) I_ds–V_ds curves measured in the dark and under the illumination whose wavelength is 514 nm and power is 5 µW. The inset shows response of the current with respect to periodic on/off of the illumination; (c) EQE under different power of 514 nm and 633 nm laser at V_ds = 0 and V_g = 0.^[86]