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DS: Fachverband Dünne Schichten

DS 55: Focused Session: Novel Green Laser Diodes (jointly with HL and O)

DS 55.5: Hauptvortrag

Donnerstag, 17. März 2011, 16:45–17:15, POT 51

Optical gain of green (Al,In)GaN laser diodes — •Ulrich Schwarz — Fraunhofer IAF, Freiburg, Germany — IMTEK, University of Freiburg, Germany

To achieve lasing in the green spectral region with group III-nitrides, InGaN quantum wells with Indium content larger than 25% are necessary. It is extremely difficult to find growth conditions which are producing homogeneous InGaN quantum wells without dark spots at this high Indium content. Both, the density of nonradiative recombination centers and the width of inhomogeneously broadened photoluminescence spectra increase with Indium content. The consequences are broadened optical gain spectra and lower differential gain. For green laser diodes amplified spontaneous emission sets in far below lasing threshold due to the low differential gain. Going from c-plane to semi- and non-polar oriented quantum wells the differential gain as function of carrier density increases. However, the carrier liefetime decreases, lowering the differential gain as function of current density. The orientation of the quantum well has also an impact on the width of the gain spectra, both through intrinsic band structure effects and through dependency of the growth conditions and Indium fluctuations on the individual growth plane. For semipolar quantum wells also the effect of birefringence on the waveguide modes and optical gain has to be considered.