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HL: Fachverband Halbleiterphysik

HL 76: Nitride-based Green Lasers

HL 76.4: Talk

Thursday, March 17, 2011, 12:30–12:45, POT 51

Strain Relaxation Mechanisms in Green Emitting GaInN/GaN Laser Diode Structures — •Lars Hoffmann¹, Heiko Bremers¹, Holger Jönen¹, Uwe Rossow¹, Johannes Thalmair², Josef Zweck², Marco Schowalter³, Andreas Rosenauer³, and Andreas Hangleiter¹ — ¹TU Braunschweig, Institute of Applied Physics, Braunschweig, Germany — ²Universität Regensburg, Institut für Experimentelle und Angewandte Physik, Regensburg, Germany — ³Universität Bremen, Institute of Solid State Physics, Bremen, Germany

While GaN-based blue light emitting devices exhibit exceptionally large internal quantum efficiencies (up to 80% at room temperature) their green counterparts quickly become less efficient at longer wavelength ("green gap"). Green emitting laser diodes based on polar as well as non- and semipolar planes have also been demonstrated, but it remains increasingly difficult to push the emission to longer wavelength. Using Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) we have studied ultrathin (< 2nm) high indium content quantum well (QW) structures suitable for blue-green laser diodes. We investigate the mechanisms of relaxation and possible misfit dislocation generation in c-plane LD structures, partial relaxation and thermal degradation. We observe threading dislocations (TD) bending by several degrees at highly strained interfaces. The results indicate that larger lattice mismatch strain leads to larger bend angles. Furthermore, if two of those TDs are crossing each other, they could annihilate and reduce the TD density.