Galvanized by high volume applications like water purification, disinfection of appliances and air filtering systems the development of light emitting diodes in the ultraviolet spectral range (UV-LEDs) has significantly intensified, with a focus on LEDs emitting near the germicidal effectiveness peak around 270 nm [1]. This presentation will provide an overview of the state-of-the art in UV-LED technologies and discuss recent advances in the development of low defect density AlGaN heterostructures and AlN base layers on sapphire substrates [2]. We will demonstrate high power AlGaN quantum well LEDs emitting near 270 nm and explore the wavelength limits of deep UV-LEDs with emission as short as 217 nm. These deep UV-LEDs are ideally suited for sensing applications like the monitoring of toxic gases, nitrates in water, and may also be utilized for the in-vivo inactivation of multi-drug-resistant germs and airborne viruses without damaging the human skin. However, a strong decline in the external quantum efficiency (EQE) can be observed for UV-LEDs below 250 nm. We will investigate the root causes for the drop in EQE at deep UV wavelengths, including changes in the optical polarization of light emission and their effects on light extraction as well as changes in radiative recombination rates and the role of point defects in AlGaN materials with high aluminium mole fractions. Based on these advances, milliwatt power LEDs emitting near 233 have been realized [3] and the first spectrally pure deep UV LED irradiation module for the in-vivo inactivation of multi-drug-resistant bacteria is demonstrated [4].

 

References

[1] M. Kneissl, J. Rass (Eds.), III-Nitride Ultraviolet Emitters - Technology & Applications (Springer, Cham, Heidelberg, New York, 2016).

[2] M. Kneissl, T.-Y. Seong, J. Han, H. Amano, "The emergence and prospects of deep ultraviolet light emitting diode technologies", Nature Photonics 13, 233 (2019).

[3] N. Lobo-Ploch et al., “Milliwatt power 233 nm AlGaN-based deep UV-LEDs on sapphire substrates”, Appl. Phys. Lett. 117, 111102 (2020).

[4] M.C. Meinke et al., „Krankenhauskeime mit UVC-Leuchtdioden bekämpfen“, Management & Krankenhaus 9, 20 (2020).