Fig. 4.

Photo-responsivity and polarization-sensitivity in 10-layer mid-IR BP photodetector. a Photo-responsivity as a function of source-drain bias at charge-neutrality points. For 3.4, 5, and 7.7 μm incident lasers, the back gate bias is 0, 30, and 35 V, respectively, and the incident laser powers are 40, 50, and 100 μW, respectively. b NEP and dark currents at charge-neutrality points at the three representative mid-IR wavelengths. For photocurrent measurements at 3.4, 5, and 7.7 μm, the back gate bias is 0, 30, and 35 V, respectively. c Scatters show the photocurrent at different laser polarizations for the 5 μm incident laser. The incident power is 50 μW. Here the incident angle of 0° corresponds to the laser polarization aligned with the X-direction (armchair) of BP. Solid lines are fitting curves from the equation $I=\left(I_{\max }-I_{\min }\right){\cos }^2\theta +I_{\min }$, where θ is the polarization angle referenced to the X-direction of BP, and I _max and I _min are the photocurrent intensities along X- and Y-direction, respectively