Hillock Related Degradation Mechanism for AlGaN-Based UVC LEDs

Heteroepitaxial growth of high Al-content AlGaN often results in a high density of threading dislocations and surface hexagonal hillocks, which degrade the performance and reliability of AlGaN-based UVC light emitting diodes (LEDs). In this study, the degradation mechanism and impurity/defect behavior of UVC LEDs in relation to the hexagonal hillocks have been studied in detail. It was found that the early degradation of UVC LEDs is primarily caused by electron leakage. The prominent contribution of the hillock edges to the electron leakage is unambiguously evidenced by the transmission electron microscopy measurements, time-of-flight secondary ion mass spectrometry, and conductive atomic force microscopy. Dislocations bunching and segregation of impurities, including C, O, and Si, at the hillock edges are clearly observed, which facilitate the trap-assisted carrier tunneling in the multiple quantum wells and subsequent recombination in the p-AlGaN. This work sheds light on one possible degradation mechanism of AlGaN-based UVC LEDs.

Automated summary

Heteroepitaxial growth of high Al-content AlGaN often leads to threading dislocations and surface hexagonal hillocks, which degrade the performance and reliability of AlGaN-based UVC LEDs. This study investigates the degradation mechanism and impurity/defect behavior of UVC LEDs in relation to the hexagonal hillocks. Electron leakage is found to be the main cause of early degradation in UVC LEDs. The role of hillock edges in electron leakage is confirmed by transmission electron microscopy measurements, time-of-flight secondary ion mass spectrometry, and conductive atomic force microscopy. Dislocations bunching and segregation of impurities at the hillock edges facilitate trap-assisted carrier tunneling and recombination in the p-AlGaN. This work provides insights into a possible degradation mechanism of AlGaN-based UVC LEDs.