Sb₂Te₃–Bi₂Te₃ Direct Photo–Thermoelectric Mid‐Infrared Detection

Abstract A compact and responsive thermoelectric photodetector is introduced for the mid‐infrared. By resonantly coupling mid‐infrared light to a Sb₂Te₃‐Bi₂Te₃ thermoelectric junction, a thermocouple is formed that is directly heated by narrow‐band mid‐infrared radiation. Near‐perfect absorption is achieved at this hot junction through the resonantly enhanced coupling of light to free‐electrons in the Bi₂Te₃ and Sb₂Te₃ materials. The fabricated devices operate at 3.6 µm and demonstrate a responsivity of 10.2 V W⁻¹, a specific detectivity of 4.6 × 10⁶ cm Hz^1/2 W⁻¹, and a bandwidth in the order of 1 kHz. The optimal detection wavelength can be spectrally tuned by changing the resonant cavity dimensions. This work shows a path toward miniaturized mid‐infrared detectors and spectrometers with high sensitivity, responsivity, and bandwidth. Importantly, the device presented here is ideal for industrial production, which it is hoped will provide wider access to mid‐infrared technologies for chemical sensing, medicine, and security.