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Owing to their consistently emerging applications in modern photonics, highly sensitive and rapid mid‐infrared (MIR) photodetectors, operating at high temperatures, are of great significance. Herein, a novel PbTe/Ge heterostructure is introduced. Notably, the discovery of a 2D electron gas (2DEG) system on the surface of the PbTe layer is experimentally identified for the first time. A high‐performance PbTe/Ge heterostructure MIR photodetector utilizing a plasmonic photovoltaic effect is developed by employing asymmetric electrodes. The photodetecting device demonstrates an exceptionally high detectivity of 1.1 × 1011 Jones along with a short response time of 15 ns at room temperature. Additionally, the proposed plasmonic photovoltaic mechanism of the device is investigated and mainly ascribed to the propagating plasmons, generated by the coupling of the 2DEG with incident MIR photons. Moreover, a linear detector array (LDA) of PbTe/Ge is demonstrated for a thermal imaging application, which exhibits promising high‐quality real‐time imaging via the 2D photodetector arrays on Ge‐based integrated circuits. This work opens up a new way for the development of next‐generation, advanced MIR photonic devices and integrated photonic systems. [ABSTRACT FROM AUTHOR]

High‐speed and highly sensitive infrared photodetectors are regarded as one of the most essential components in modern photonic devices and technology because of constantly emerging application scenarios. In this paper, an ultrafast and extremely low noise mid‐infrared (MIR) photodetector is reported at both room and cryogenic temperatures by leveraging the high‐mobility 2D electron gas (2DEG) at the polar CdTe/PbTe heterostructure interface. The detector simultaneously exhibits a peak detectivity of ≈4.2 × 1011 Jones with rapid response in the order of 10 ns, which is substantially superior to the state‐of‐the‐art 2DEG MIR detectors made of 2D layered materials. The ultrafast response with extremely low noise of the 2DEG photodetector is attributed to the unique band alignment at the interface. The practical infrared imaging application is further showcased using the 2DEG MIR detector by revealing the fine features of a MIR radiation target. This work highlights the promising prospect of utilizing the unique 2DEG interface in the field of high‐speed and highly sensitive MIR detection. [ABSTRACT FROM AUTHOR]