Impact of hermetic package and UV-induced self-cleaning on the reliability of UV LEDs

J. Ruschel¹, C. Stölmacker¹, N. Lobo-Ploch¹, J.E. Boschker¹, N. Kemf¹, J. Glaab¹, T. Filler¹, T. Musengezi¹, J. Rass¹, H.K. Cho¹, M. Schilling², T. Wernicke², S. Knigge¹, M. Kneissl^1,2 and S. Einfeldt¹

Published in:

J. Phys. D: Appl. Phys., vol. 59, no. 7, pp. 075106 (2026).

Abstract:

The impact of hermeticity on the stability of the emission power of far-ultraviolet-C light-emitting diodes (UVC LEDs) emitting at 233 nm is systematically investigated. While hermetic packaging can lower the probability of catastrophic failures (CFs), it has been found that the emission power of hermetically packaged LEDs decreases significantly faster than that of non-hermetically pack aged LEDs. Depending on the operating conditions of the LED this effect can cause an additional relative emission power reduction of up to 60% after 100 h operation. The effect is also present for UVB LEDsemitting at 310 nm and thus relevant for applications in which hermetically sealed UVLEDsareoperated over long periods of time. Due to hermetic operation, a carbon-containing layer is shown to form on the sapphire surface of the bottom-emitting chip, which reduces the transmittance and thus the light extraction efficiency. The results show that the effect slows down at low operating temperatures and optimizing the mounting technology can significantly reduce the effect. Furthermore, a recovery in the LED emission power was discovered when the hermetic package was opened and further operated. The proposed explanation is that this contamination layer recedes as soon as a UV-induced self-cleaning process takes place, which is only possible with the supply of oxygen.

Keywords:

hermetic package, reliability, UV-induced self-cleaning, far-UVC LED, contamination, AlGaN-based UV LED, sapphire

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