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HL: Fachverband Halbleiterphysik

HL 19: Nitrides: Devices

HL 19.6: Vortrag

Montag, 31. März 2014, 16:15–16:30, POT 151

Sub-250 nm LEDs with enhanced charge carrier injection — •C. Kuhn¹, F. Mehnke¹, M. Guttmann¹, C. Reich¹, T. Kolbe¹, V. Kueller², A. Knauer², T. Wernicke¹, M. Weyers², and M. Kneissl^1,2 — ¹Technische Universität Berlin, Institut für Festkörperphysik, Germany — ²Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Berlin, Germany

For AlGaN-based LEDs emitting at 250 nm and below, the aluminum content of the active region and surrounding layers exceeds 60%. For LEDs with such high Al mole fractions, carrier injection is a major challenge due to increasing donor and acceptor activation energies and small band offsets between AlGaN quantum wells (QW), barriers and electron blocking layers (EBL). In this study, we investigate the influence of the AlN/Al_0.7Ga_0.3N:Mg electron blocking heterostructure on the injection efficiency of 245 nm LEDs. Increasing thickness of the AlN EBL leads to a rise of the QW luminescence for Mg-doped and undoped AlN layers. However, there is still strong parasitic luminescence centered at 280 nm which depends on the Mg supply during the AlN EBL growth. AlN EBLs grown without Mg enable a drastic reduction of the parasitic luminescence, if the AlN thickness is larger than 4 nm. We were able to demonstrate 245 nm LEDs with an 8 nm thick undoped AlN EBL with external quantum efficiency of 0.19%. Finally, this improved design was applied to UV-C LEDs with different emission wavelengths. AlGaN-based LEDs in the emission range between 235 nm and 263 nm were demonstrated with maximum EQE of 1.1% at 263 nm.