Germanium/Silicon Single-Photon Avalanche Diodes for SWIR Applications: A Review

Ge/Si single-photon avalanche diodes (SPADs) play a pivotal role in advancing silicon-based optoelectronics by enabling high-sensitivity photodetection at short-wave infrared wavelengths, a critical region for applications such as quantum communication, light detection and ranging (LiDAR), and biological imaging. This review provides a comprehensive overview of Ge/Si SPAD, analyzing the fundamental principles, key performance factors, and optimization methods, including material growth, interface engineering, and structural design. We detail the evolution of major Ge/Si SPAD structures: the initial mesa type with simple design; the planar type, which enhances performance through precise doping; and the lateral type, which simplifies fabrication and innovatively combines vertical absorption with horizontal multiplication. These advancements have driven Ge/Si SPAD toward higher single-photon detection efficiency (SPDE), lower dark count rate (DCR), broader operational wavelengths, and high-performance room-temperature operation. Ongoing structural optimizations not only expand design options but also contribute significantly to the advancement of silicon-based optoelectronics.