Berlin 2012 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 63: Devices I
HL 63.8: Vortrag
Mittwoch, 28. März 2012, 16:45–17:00, EW 015
Efficiency droop in nonpolar InGaN quantum wells — •Lukas Schade1,2, Ulrich Schwarz1,2, Tim Wernicke3, Jens Rass3, Simon Ploch3, Markus Weyers4, and Michael Kneissl3,4 — 1Fraunhofer Institut für Angewandte Festkörperphysik (IAF), Freiburg — 2Institut für Mikrosystemtechnik (IMTEK), Universität Freiburg — 3Institut für Festkörperphysik, Technische Universität Berlin — 4Ferdinand-Braun-Institut (FBH), Berlin
InGaN quantum wells (QWs) exhibit a decline of the internal efficiency at high charge carrier excitation. This has been observed for polar as well as for semipolar and nonpolar oriented QWs. Polar stands for the (0001) growth direction with strong piezoelectric fields. Due to the vanishing fields, the orthogonal growth directions (a or m) are called nonpolar, while all directions between are merged as semipolar orientations. In contrast to the polar and many semipolar QWs, nonpolar InGaN QWs provide a special property: optical polarization of the radiative transitions, which is a result of the anisotropic strain within pseudomorphic grown nonpolar QWs. Using this property, the broadened effective emission can be resolved into two fundamental transitions. They are spectrally separated by a defined energy which corresponds to the energy distance of the valence subbands. We studied nonpolar InGaN/InGaN Multi-QWs grown on low defect density GaN substrates with a setup for confocal microscopy. To reach high excitation densities of charge carriers, we use either a combination of an UV laser and highly focusing objectives or an electric pulse generator. The emission is spectrally analysed and compared to established models.