Hillock Related Degradation Mechanism for AlGaN-Based UVC LEDs

Area of Science:

• Materials Science
• Semiconductor Physics
• Optoelectronics

Background:

• Heteroepitaxial growth of high Al-content AlGaN leads to defects like threading dislocations and hexagonal hillocks.
• These defects degrade the performance and reliability of ultraviolet-C (UVC) light-emitting diodes (LEDs).

Purpose of the Study:

• To investigate the degradation mechanism of UVC LEDs.
• To understand impurity and defect behavior in relation to hexagonal hillocks.
• To identify the primary cause of early UVC LED degradation.

Main Methods:

• Transmission electron microscopy (TEM).
• Time-of-flight secondary ion mass spectrometry (ToF-SIMS).
• Conductive atomic force microscopy (C-AFM).

Main Results:

• Early UVC LED degradation is primarily attributed to electron leakage.
• Hillock edges significantly contribute to electron leakage.
• Dislocation bunching and segregation of impurities (C, O, Si) at hillock edges were observed.
• These defects facilitate trap-assisted carrier tunneling and recombination.

Conclusions:

• Hexagonal hillocks and associated impurity/defect segregation are critical factors in UVC LED early degradation.
• Understanding these mechanisms is crucial for improving UVC LED reliability and performance.