An IR phototransistor is developed based on a feedback field effect transistor (FBFET) having a Si-pnpn structure composed of a p-type drain, n-type channel1, p-type channel2, and n-type source. The gate contact is eliminated in the new device, referred to as light-triggered (LT) FBFET, and a SiGe layer replaces the channel2 to absorb IR light. Instead of the bias applied to the gate contact, the open circuit voltage generated by IR absorption in the SiGe layer controls the current flowing from the drain to the source. With a 2-dimensional periodic array of LT-FBFETs, a metasurface having a resonance is constructed, leading to substantial enhancement of IR absorption in the SiGe layer. Owing to the near-zero subthreshold swing, high on/off ratio, and small off current of FBFETs, the LT-FBFET provides high external quantum efficiency and low static power dissipation.
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