A Combination of Ion Implantation and High-Temperature Annealing: The Origin of the 265 nm Absorption in AlN

The commonly observed absorption around 265 nm in AlN is hampering the outcoupling efficiency of light-emitting diodes (LEDs) emitting in the UV-C regime. Carbon impurities in the nitrogen sublattice (C-N) of AlN are believed to be the origin of this absorption. A specially tailored experiment using a combination of ion implantation of boron, carbon, and neon with subsequent high-temperature annealing allows to separate the influence of intrinsic point defects and carbon impurities regarding this absorption. Herein, the presented results reveal the relevance of the intrinsic nitrogen-vacancy defect V-N. This is in contradiction to the established explanation based on C-N defects as the defect causing the 265 nm absorption and will be crucial for further UV-LED improvement. Finally, in this article, a new interpretation of the 265 nm absorption is introduced, which is corroborated by density functional theory (DFT) results from the past decade, which are reviewed and discussed based on the new findings.

Automated summary

The presence of carbon impurities in AlN was believed to be the main cause of the absorption at 265 nm. However, this study revealed that the intrinsic nitrogen-vacancy defect V-N plays a crucial role in the absorption. This finding is significant for further improvement of UV-LEDs.