(a) Schematic of the waveguide-integrated few-layer BP photodetector. (b) The frequency response of the waveguide-integrated BP photodetector at low doping state (V_G=−8 V) and high doping state (V_G=8 V). (c) Two-dimensional contour plot of photocurrent versus the gate voltage V_G and the bias voltage V_DS. (d) The intrinsic responsivity R and internal quantum efficiency IQE as a function of applied bias for different thicknesses. t_BP: the thickness of BP. Panels (a)–(d) are reproduced from Ref. [103] with permission from the Nature Publishing Group.