Berlin 2015 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 40: Focus Session: Role of polarization fields in nitride devices I

HL 40.4: Vortrag

Mittwoch, 18. März 2015, 10:30–10:45, ER 164

Optical polarization of AlGaN quantum well LEDs with emission wavelength near 245 nm — •Martin Guttmann¹, Christoph Reich¹, Frank Mehnke¹, Christian Kuhn¹, Tim Wernicke¹, Jens Rass^1,2, Mickael Lapeyrade², Sven Einfeldt², Arne Knauer², Viola Kueller², Markus Weyers², and Michael Kneissl^1,2 — ¹Institute of Solid State Physics, Technische Universität Berlin — ²Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Berlin

For Al_xGa_1−xN quantum wells (QWs) the order of the valence bands at the center of the Brillouin zone depends on the aluminum content and the strain state, and hence the optical polarization of the in-plane emission. We measured the optical polarization of AlGaN quantum well light emitting diodes (LEDs) with emission wavelength between 235 nm and 265 nm, corresponding to an aluminum content between 80% and 60% in the QWs. We observed a dominant TE emission for the compressively strained AlGaN multiple quantum wells in the entire wavelength range. The degree of polarization, i.e. (I_TE−I_TM)/(I_TE+I_TM), decreases from 0.85 at 265 nm to 0.5 at 239 nm. From the TE/TM spectra and the temperature dependent polarization we were able to determine the energy difference between the two topmost valence bands to be e.g. 30 meV for 243 nm LEDs. The deviation from the expected splitting energy of -150 meV for unstrained Al_0.7Ga_0.3N QWs can be explained by the large compressive strain in the QWs.