Violet-emitting diode lasers on low defect density GaN templates

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.