Regensburg 2007 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 42: GaN: devices
HL 42.8: Talk
Thursday, March 29, 2007, 15:45–16:00, H13
Direct Observation of Substrate Modes in 405 nm (Al,In)GaN Laser Diodes — •Harald Braun1, Christoph Lauterbach1, Ulrich T. Schwarz1, Valerio Laino2, Bernd Witzigmann2, Christian Rumbolz3, Marc Schillgalies3, Alfred Lell3, Volker Härle3, and Uwe Strauß3 — 1NWF II Physik, Universität Regensburg, Universitätsstr. 31, 93053 Regensburg — 2Integrated Systems Laboratory, ETH Zurich - Gloriastrasse 35, CH-8092 Zurich, Switzerland — 3Osram Opto Semiconductors GmbH, Leibnizstr. 2, 93055 Regensburg
In (Al,In)GaN laser diodes high refractive index epitaxial layers like the SiC or GaN substrate can act as parasitic waveguides. The resulting substrate modes cause losses to the mode propagating in the laser waveguide, so an impact on laser threshold and gain spectra can be seen. We also observe the standing wave in the substrate directly by a measurement of the near-field intensity on the cleaved surface of the substrate just below the laser ridge waveguide. The oscillation period of the substrate modes extracted from these measurements varies strongly from sample to sample with nominally the same epitaxial structure. By a simple refractive index model we calculate the corresponding effective refractive index of the laser waveguide and the angle of the far-field side lobe and compare the results with far-field measurements. Furthermore we put forward a complex two-dimensional simulation of the optical field distribution in the laser structure including the SiC or GaN substrate. These simulations allow a quantitative interpretation of the experimental features caused by the substrate modes.