Rugged GaN UV-APDs via Engineered Bevel-Edge Angle Under Accelerated Avalanche Stress

The avalanche ruggedness of GaN ultraviolet avalanche photodiodes (UV-APDs), critical for reliable Geigermode operation, is systematically evaluated for the first time via an accelerated stress methodology. APDs with an ultra-shallow bevel edge termination (2.5°) exhibit superior ruggedness, withstanding a static avalanche current density of 102A/cm2at room temperature and accelerated avalanche stress at 175 °C. In contrast, inherent instabilities are revealed in APDs with a conventional-shallow (12°) bevel edge. Degradation modes observed under stress included avalanche current increase after room-temperature stress and destructive breakdown at high temperature. The degradation mechanism is attributed to the trap-assisted charge dynamics at the mesa sidewall, a process driven by the high local electric field at the mesa sidewall. This degradation is effectively mitigated by the ultra-shallow 2.5°-bevel structure, which significantly reduces the sidewall electric field. The resulting high stability establishes a new benchmark for GaN APD reliability.