Dresden 2017 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 72: Nitrides: Devices
HL 72.4: Talk
Thursday, March 23, 2017, 10:15–10:30, POT 06
Enhanced light extraction and internal quantum efficiency for UVB LEDs with UV-transparent p-AlGaN superlattices — •Martin Guttmann1, Martin Hermann1, Johannes Enslin1, Sarina Graupeter1, Luca Sulmoni1, Christian Kuhn1, Tim Wernicke1, and Michael Kneissl1,2 — 1Technische Universität Berlin, Institute of Solid State Physics — 2Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Berlin
Light emitting diodes (LEDs) in the UVB spectral range (280 nm - 315 nm) are of particular interest for applications such as plant growth lighting and phototherapy. State-of-the-art devices utilize highly absorbing p-GaN contacts and low aluminum mole fraction p-AlGaN layers to enable low operating voltages. The exploitation of UV-transparent p-AlGaN layers together with highly UV-reflective metal contacts may significantly increase the light extraction efficiency (LEE). In this paper, the light output of LEDs emitting around 310 nm with UV-transparent and absorbing Mg-doped AlGaN superlattices is compared. A three-fold increase of the external quantum efficiency (EQE) was observed for LEDs with UV-transparent p-AlGaN layers. To investigate these findings, LEDs with low-reflectivity Ni/Au and high-reflectivity Al contacts were fabricated, characterized, and ray tracing simulations were performed. The increased EQE can be partially ascribed to an two-fold improved LEE in combination with a 50% increase of the injection and internal quantum efficiency when using a UV-transparent p-Al0.4Ga0.6N/Al0.6Ga0.4N-superlattice.