Silicon-based Single Photon Avalanche Diode Technologies: Structures, Performance, and Challenges

Solid-state Single Photon Avalanche Diodes (SPADs) have emerged as versatile photodetectors, playing a pivotal role in cutting-edge technologies such as photon counting, timing, and imaging. Their exceptional characteristics — high timing resolution, fast response, high gain, excellent quantum efficiency, and immunity to magnetic fields — make them a compelling alternative to traditional Photomultiplier Tubes (PMTs). SPADs’ unique ability to detect single photons, combined with their digital output and compact size, has positioned them as a superior choice for a wide range of applications in engineering, environmental monitoring, and healthcare. This review provides a comprehensive analysis of SPAD technology, focusing on their design principles, performance metrics, and applications. We begin by exploring the fundamental operating principles of SPADs and their key performance metrics. Next, we examine various SPAD structures across different technology nodes, offering a comparative analysis to highlight the latest advancements. Based on our review, we identify several techniques to enhance SPAD performance, including: doping profile engineering such as using high-voltage layers and doping compensation layers; upgrading optical stacks; and integration of high-speed front-end circuitry. We then introduce application-specific figures-of-merit and assess their relevance to the reviewed structures. Additionally, we address emerging trends in SPAD design, such as leveraging mask layer technology to achieve significant advancements. Finally, we conclude with an overview of research challenges, potential solutions, and future directions in SPAD technology, providing valuable insights to drive further innovations in this dynamic field.