For low-power optical communication, the switching energy is an important device parameter. For a measurement with zero bias, there is no additional energy cost for the applied voltage and the switching energy amounts to < 27 fJ/bit upon dividing a typical incident laser power of 6.25 µW by the (set-up limited) 230 MHz bandwidth. Using a square pulse laser with comparable output power (2 µW) and irradiance (100 W/cm 2 ), we calculate the responsivity of the device under typical operating conditions as 50 mA/W using the ON/OFF characteristics in Figure . We note a strong power-dependence of the responsivity with quickly declining values at higher powers in line with earlier reports. Under the assumption that the dark current dominates the noise, we calculate the specific detectivity according to: 𝐷 * = 𝑅 * √𝐴 √2𝑞 * 𝐼 𝑑𝑎𝑟𝑘 ⁄ = 3.9 * 10 10 𝐽𝑜𝑛𝑒𝑠, with 50 mA/W for the responsivity, an area A of 20 µm 2 , the electron charge q and a dark current of 1 pA. We obtain the external quantum efficiency as 𝐸𝑄𝐸 = 𝑅 * ℎ𝜈 𝑞 ⁄ with the responsivity, Planck's constant, the frequency and the electron charge respectively. With a responsivity of 50 mA/W at a wavelength of 636 nm this yields a value of approximately 10 % which is in good agreement with earlier reports. 23