Preparation and research progress of GaN-based avalanche photodetectors

The demand for single-photon high-sensitivity ultraviolet (UV) detection is continuously increasing in cutting-edge fields such as UV astronomy, environmental monitoring, and space communications. In particular, gallium nitride (GaN) is an ideal material for UV detection due to its wide bandgap (3.4 eV), strong radiation immunity and visible/solar-blind properties. In this respect, avalanche photodetectors (APDs) are very promising candidates for single-photon UV detection due to high sensitivity, large gain, high detection efficiency, and room temperature operation. This review summarizes the GaN avalanche breakdown characteristics, including current surge, positive temperature coefficient of Breakdown Voltage (BV), and non-linear characterization. In addition, recent advances in various structural types of GaN APDs, such as p-i-n, separated absorption multiplication (SAM), optimized edge termination, and polarization-enhanced structures, are presented. In addition, the directions and challenges for the future development of GaN APDs are discussed. Although GaN-based APDs have significantly improved their UV single-photon detection performance through structural innovations, noise control, linearity optimization, and process simplification remain the core challenges. In the future, the integration with two-dimensional material heterojunction and new light trapping structure is expected to break through the existing bottleneck and promote its application in frontier fields such as deep space exploration and quantum communication.