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HL: Fachverband Halbleiterphysik
HL 69: Nitrides: LEDs
HL 69.1: Talk
Thursday, March 17, 2011, 10:15–10:30, POT 51
Optical polarization of UV-A and UV-B (In)(Al)GaN multiple quantum well light emitting diodes — •Tim Kolbe1, Arne Knauer2, Joachim Stellmach1, Chris Chua3, Zhihong Yang3, Sven Einfeldt2, Patrick Vogt1, Noble M. Johnson3, Markus Weyers2, and Michael Kneissl1,2 — 1Institute of Solid State Physics, TU Berlin, Hardenbergstr. 36, 10623 Berlin, Germany — 2Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin, Germany — 3Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304, USA
The optical polarization of the in-plane electroluminescence of (0001) oriented (In)(Al)GaN multiple quantum well light emitting diodes (LEDs) in the spectral range from 288 nm to 386 nm has been investigated. A decrease of the intensity of transverse-electric (TE) polarized light relative to transverse-magnetic (TM) polarized light with decreasing emission wavelength is found. This effect is attributed to rearrangement of the valence bands at the gamma-point of the Brillouin zone with changing aluminum and indium mole fractions in the (In)(Al)GaN quantum wells. For shorter wavelengths the crystal-field split-off hole band moves closer to the conduction band relative to the heavy and light hole bands. As a consequence TM polarized emission from the split-off hole band becomes more dominant for LEDs with a decreasing emission wavelength. A polarization of zero (that means that the intensities of the TE polarized light and the TM polarized light are the same) is found for LEDs emitting near 300 nm. For shorter wavelengths the emitted light is mainly TM polarized.