Michael Kneissl Seminar

Speaker: Michael Kneissl

Affiliation: Institute of Solid State Physics, Technische Universität Berlin, Berlin, Germany &

Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Berlin, Germany

Topic: Exploring the wavelength limits of AlGaN-based deep UV emitters

This presentation will provide an overview of recent advances in the growth of high quality AlGaN materials by metalorganic vapour phase epitaxy (MOVPE) as well as UV-LED device technologies. We will discuss novel approaches to improve the internal and external quantum efficiency of UV light emitters, including the growth of low defect density AlN layers on sapphire substrates by epitaxial lateral overgrowth (ELO) and low resistance n-AlGaN current spreading layers at aluminium mole fractions exceeding 80%. We will present efficient carrier injection into AlGaN-based LEDs emitting below 240 nm based on Mg-doped Al(Ga)N/AlGaN electron blocking heterostructures and examine advanced methods for light extraction, e.g. by controlling the optical polarization of the emission from deep UV AlGaN quantum wells or by utilizing UV-transparent graphene electrodes. We have been able to realize (In)AlGaN multiple quantum well LEDs in the wavelength range between 340 nm and 230 nm and demonstrate UVB-LED arrays near 310 nm with output powers of more than 50 mW and estimated lifetimes of 10,000 hours. Finally, we will illustrate how today’s UV-LEDs are being already successfully applied in flow cytometry, plant growth lighting and sensing, and how they may impact other applications in the near future like water purification, medical diagnostics, and phototherapy.