Solid-state avalanche photodiodes (APDs) based on AlGaN with Al composition exceeding 40% are being heavily stud-ied because they have intrinsic solar-blindness, which could be a viable alternative to Si-based photodiodes or photo-multiplier tube (PMT) used in ultraviolet (UV) military, civilian and scientific areas. However, the development of the solar-blind AlGaN APDs with high gain has been still suffered from some problems, such as low p-type doping effi-ciency and high dislocation densities for high-Al content AlGaN layer. In addition, the breakdown voltages of the con-ventional AlGaN APDs are generally more than 90 V, which results in a large leakage current. Large dark current can increase the device noise, as well as confine the APDS avalanche gain.