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HL: Fachverband Halbleiterphysik

HL 6: Quantum dots and wires: preparation and characterization I

HL 6.3: Vortrag

Montag, 26. März 2007, 11:30–11:45, H15

Transferring achievements of quantum dot test structures to laser devices — •Tim David Germann, André Strittmatter, Thorsten Kettler, Kristijan Posilovic, Udo W. Pohl, and Dieter Bimberg — Institute of Solid State Physics, Sekr. PN 5-2, Hardenbergstr. 36, Technical University of Berlin, D-10623 Berlin, Germany

Fabrication of quantum dot (QD) based lasers for 1.3 µm emission and beyond requires a better understanding of epitaxial processes of the active QD region. The lasing wavelength of QD layers grown by MOCVD is typically blue shifted with respect to the ground state photoluminescence of test structures. We identified mechanisms driving the blue shift and developed techniques to reduce or even suppress this shift. A crucial parameter is the V/III ratio during the process of overgrowing the QDs with GaAs. High V/III ratios promote the blue shift due to a preferential formation of group-III vacancies at the surface. This increases group-III diffusion, leading to smaller QDs with less In content. In contrast, by using low V/III ratios, negligible blue shift of the photoluminescence is observed for laser structures.

However, laser diodes grown with low V/III ratios showing QD ground state emission at 1270-1280 nm still exhibit lasing at only 1220-1240 nm. This shift is shown to originate from gain saturation of the ground state emission and contributions of excited states emission. The growth of the p-doped AlGaAs cladding layer and the highly p-doped GaAs contact layer may affect the luminescence properties of the active region and induce fast saturation. Strategies and achievements to overcome this limit are discussed.