Ultraviolet Photon Detection in CMOS Single-Photon Avalanche Diodes: A Review

Ultraviolet (UV) imaging is enabling a growing range of applications in industrial inspection, biomedicine, and aerospace. Single-photon avalanche diodes (SPADs), known for their exceptional sensitivity and fast timing resolution, have achieved remarkable success in visible and near-infrared (NIR) applications, e.g., in LiDAR. However, there remains a significant gap in the development and deployment of UV SPAD detectors. This review presents the latest progress, challenges, and application potential of SPAD technologies in deep-UV (DUV) and near-UV (NUV) ranges. It reviews the challenges in UV detection and the currently reported NUV SPADs, including wide-bandgap semiconductors (WBSs) avalanche photodiodes (APDs), silicon-based SPADs with front-side illumination (FSI) and back-side illumination (BSI), and silicon photomultipliers (SiPMs). By linking UV imaging with single-photon detection, this review aims to support future silicon-based complementary metal-oxide-semiconductor (CMOS) high-speed, large-format UV SPAD arrays and their integration into nextgeneration imaging systems.