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The issue of destructive breakdown and high dark current in AlGaN ultraviolet avalanche photodiodes has conventionally been attributed to material defects, yet direct evidence supporting this claim has been absent. Examining damaged devices that experienced destructive breakdown revealed an intriguing finding: post-treatment with a potent alkali resulted in the emergence of corrosion pits on the device's surface. Subsequently, a dry etching process was implemented in the targeted area to eliminate the corrosion pit. Remarkably, the current–voltage measurement subsequent to this treatment showcased a complete restoration of the damaged device's previous performance. This unequivocally indicates that the destructive breakdown was localized, and the point of punch-through could be precisely identified through the corrosion pit. Consequently, it is now firmly believed that material defects constitute the primary cause of destructive breakdown in these instances. [ABSTRACT FROM AUTHOR]

Aluminum nitride (AlN) is one of the highly anticipated materials for deep-ultraviolet (UV) optoelectronic devices due to its wide-bandgap and high thermal conductivity. Growing a thick singlecrystal AlN layer by Hydride Vapor Phase Epitaxy (HVPE) method on another AlN substrate generated by Physical Vapor Transport (PVT) method is an effective method to obtain pure single crystal AlN. However, the waste of PVT-AlN is a serious obstruct for industrialization. In this study, the laser slicing of HVPE-AlN and PVT-AlN by femtosecond laser pulses was performed. The surface roughness of the separated HVPE-AlN was smaller than 120µm, while the separated PVT-AlN substrate was successfully used to grown a new single crystal AlN by HVPE after polishing. Femtosecond laser double spots scanning by using a SLM was also investigated to improve the efficiency. [ABSTRACT FROM AUTHOR]