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.