Different I–V Behaviors and Leakage Current Mechanisms in AlGaN Solar-Blind Ultraviolet Avalanche Photodiodes

The different current–voltage (I–V) behaviors and leakage current mechanisms of AlGaN solar-blind ultraviolet avalanche photodiodes (APDs) have been investigated to better understand the relationships between multiplication gain and threading dislocations (TDs) in wide band gap AlGaN materials. The cross-sectional transmission electron microscopy (TEM) and first-principles calculations were used to study the types, location, density, and electronic structures of threading dislocations. The I–V behaviors of APDs for different types of dislocations were simulated based on the nonlocal band-to-band tunneling model; we found that 4-core-edge TDs in the avalanche region can give rise to electron tunneling from the valence band of p-AlGaN to the conduction band of i-AlGaN and results in a premature breakdown, and the multiplication gain were significantly reduced under high electric field. The dark current of avalanche devices with high gain were dominated by open core and full core screw TDs.