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Violet-emitting diode lasers on low defect density GaN templates

Violett emittierende Diodenlaser auf defektreduzierten GaN-Templates
: Sommer, F.; Vollrath, F.; Kunzer, M.; Pletschen, W.; Müller, S.; Köhler, K.; Schlotter, P.; Wagner, J.; Weimar, A.; Haerle, V.


Physica status solidi. C 2 (2005), No.7, pp.2849-2853
ISSN: 1610-1634
ISSN: 1610-1642
ISSN: 1862-6351
Journal Article
Fraunhofer IAF ()
GaN; InGaN; laser; short-wavelength; kurzwellig; kurze Wellenlänge; defect density; Defektdichte

We compare the electro-optical characteristics of violet-emitting ridge waveguide (AlGaIn)N quantum well diode lasers with etched laser facets, grown on GaN templates with a homogeneously reduced defect density, with those of reference devices grown on sapphire using conventional low-temperature GaN nucleation layer technology. Defect densities of the former and latter laser structures were around 1x10(exp 8) cm-2 and 2x10(exp 9) cm-2, respectively. In on-wafer pulsed-mode operation a 35% reduction in threshold current density and 40% reduction in injected electrical power at threshold was achieved upon reduction of defect density. Minimum values for threshold current density and injected electrical power at threshold are 7.5 kA/cm2 (500 mu m x 4 mu m) and 0.9 W (500 mu m x 2 mu m), respectively, for a ridge laser with uncoated facets. For improved heat sinking the sapphire substrate of selected laser diodes on GaN template was removed using laser lift-off, followed by n-side down soldering on copper heat sinks. This way, the maximum duty-cycle, limited by premature thermal rollover, could be increased by a factor of three for the substrate-less lasers.