Fig. 3: BPVE generation under sub-MoS2-bandgap illumination.
From: Dual polarization-enabled ultrafast bulk photovoltaic response in van der Waals heterostructures
a Optical image of the MoS2/BP BPV device with two pairs of electrodes, where the electrodes E1-E2 are parallel to the mirror plane of the device, while the E3-E4 are perpendicular to the mirror plane. The yellow and green curves outline the monolayer MoS2 and BP, respectively. The inset shows that the excitation with 780 nm (1.589 eV) is below MoS2 bandgap (1.82 eV). The white scale bar is 7 μm. b, c Scanning photocurrent microscope (SPCM) images with the electrodes E1-E2 (b) and E3-E4 (c) with the 780 nm laser. The dashed gray lines highlight the overlap region of the heterostructure. The black scale bars are 4 μm. d AFM line profiles of the MoS2/BP device indicating the thicknesses of MoS2 and BP being 0.7 nm and 15 nm, respectively. e, f Photocurrent line profiles along the electrodes E1-E2 (e) and E3-E4 (f) at the MoS2/BP heterostructure region. The shaded areas indicate the positions of electrodes. g Calculated polar charge density with electron accumulation (blue) and depletion (red) in MoS2/BP heterostructure. The dashed hexagon represents the unit cell of MoS2. The dashed circles show the symmetry breaking at the heterostructure interface. The white arrow denotes the charge polarization. h Planar averaged differential charge density in MoS2/BP heterostructure. i Side view of the in-plane polarization distribution simulation in MoS2/BP heterostructure, where the charge redistribution mainly occurs in MoS2 layer.
