(color online) (a) Dark current densities versus applied bias voltage of the photodetector for different temperatures. (b) Dark current density of the photodetector versus inverse temperature under −400-mV applied bias voltage. The blue line refers to fitting to data in the temperature range between 250 K and 300 K, and the green line represents fitting to data in the temperature range between 100 K and 250 K. (c) Johnson noise limited detectivity of the photodetector measured under different applied bias voltages at a temperature of 300 K.