Cryogenic‐Temperature Deposited High Quality Te/Ge Heterojunction for Broadband and Fast Photodetection

Abstract Heterogeneous integration of various semiconductors is critical for broadband photodetection, yet current van der Waals integration techniques of 2D and 3D semiconductors face challenges in low process temperature, high‐quality heterointerface, and large‐scale fabrication. Here, a cryogenic‐temperature depositing strategy is presented for fabricating large scale and high‐quality tellurium (Te)/germanium (Ge) heterojunctions, leveraging the narrow bandgap (≈0.33 eV) of Te for broadband photodetection. By employing cryogenic thermal evaporation, wafer‐scale uniformity is achieved in 4‐inch Te films on Ge substrates, with a low roughness of ≈0.71 nm and large crystalline domains on the order of micrometers square. The fabricated Te/Ge heterojunction photodetector exhibits a broadband photoresponse from visible to mid‐infrared and a high performance including a linear dynamic range of 102.5 dB, a responsivity of 0.73 A W −1 , a specific detectivity of 8.47 × 10 10 cm Hz 1/2 W −1 , and rapid rise/fall times of 22 µs/14 µs at zero bias. The superior performance is attributed to the formation of a type‐II heterojunction with a native GeO x interlayer (≈3 nm) for quantum tunneling, which suppresses dark current. Furthermore, an 8 × 8 photodetector array is demonstrated and shows an exceptional uniformity. This work establishes Te/Ge heterojunctions as a versatile platform for next‐generation broadband photodetectors.