Figure 3.

a) I _DS measured in the dark and under the laser irradiation with different irradiation intensities. V _DS was swept from 0 to 72.75 V with a step of 0.25 V. The inset shows a schematic illustration of laser irradiation to a MoS₂ FET. b) Photoresponsivity and detectivity calculated under the irradiation with the intensity of 0.23 µW cm⁻² versus V _DS. The inset shows the photoresponsivity (R) of the same device calculated under the irradiation with the intensity of 2.5 µW cm⁻² at V _DS from 0.25 to 2.5 V. Schematics of energy band diagrams in the off state of MoS₂ FETs in the c) region A, d) region B, and e) region C. Red and blue symbols indicate electrons and holes, respectively. S and D denote source and drain, respectively. Two colored bands (bottom) indicate the V _DS region where carrier injection and avalanche multiplication are weak (blue) or strong (red), respectively.