Regensburg 2019 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 2: Nitrides: Devices

HL 2.7: Talk

Monday, April 1, 2019, 11:15–11:30, H31

Enhanced light extraction and internal quantum efficiency for fully-transparent AlGaN-based UVC LEDs on patterned-AlN/sapphire substrate — •Martin Guttmann¹, Anna Ghazaryan¹, Luca Sulmoni¹, Norman Susilo¹, Eviathar Ziffer¹, Tim Wernicke¹, and Michael Kneissl^1,2 — ¹Technische Universität Berlin, Institute of Solid State Physics, Berlin, Germany — ²Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Berlin, Germany

Light emitting diodes (LEDs) in the UVC spectral range utilize highly absorbing p-GaN contacts and low aluminum mole fraction p-AlGaN layers to enable low operating voltages. However, to realize high power LEDs a UVC-transparent p-side in combination with a highly reflective p-contact is necessary to increase the light extraction efficiency (LEE). In this paper, we have investigated the effect of the aluminum mole fraction in the Al_xGa_1−xN/Al_yGa_1−yN p-superlattice (p-SL) (0.32 < x < 0.65 and 0.40 < y < 0.71) and the influence of the p-contact metal reflectivity on the electro-optical properties of LEDs emitting around 265 nm. A five-fold increase of the external quantum efficiency (EQE) with a maximum value of 3.1% was observed for LEDs with UVC-transparent p-SL (x=0.65) and reflective indium contacts. In order to separate this improvement in the EQE into LEE and internal quantum efficiency (IQE), ray-tracing simulations were performed. The increased EQE can be partially ascribed to a 2.5-fold improved LEE in combination with a 2-fold increase of the IQE for the UVC-transparent Al_0.65Ga_0.35N/Al_0.71Ga_0.29N p-SL.