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27 February 2012 Effect of ridge waveguide etch depth on laser threshold of InGaN MQW laser diodes
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The laser threshold and lateral mode confinement of blue (440 nm) InGaN multiple quantum well (MQW) laser diodes have been investigated. Ridge-waveguide (RW) laser diodes with different ridge etch depth ranging from 25 nm above the active region (deep-ridge waveguide) to 200 nm above the active region (shallow-ridge waveguide) have been fabricated. The comparison of devices with the same resonator length shows that the threshold current densities are significantly lower for deep-ridge waveguide laser diodes. The difference in lasing threshold becomes more eminent for narrow ridges, which are required for single mode operation. For shallow-ridge devices the threshold current density increases by more than a factor of three when the ridge width is decreased from 20μm to 1.5μm. For the deep-ridge waveguide devices instead, the lasing threshold is almost independent of the ridge waveguide width. The effect has been analyzed by 2D self-consistent electro-optical simulations. For deep-ridge devices, the simulated thresholds and far-field patterns are in good agreement with the simulations. For shallow-ridge devices, however, questionable theoretical assumptions are needed. Two possible causes are discussed: extremely large current spreading and strong index anti-guiding.
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L. Redaelli, M. Martens, J. Piprek, H. Wenzel, C. Netzel, A. Linke, Yu. V. Flores, S. Einfeldt, M. Kneissl, and G. Tränkle "Effect of ridge waveguide etch depth on laser threshold of InGaN MQW laser diodes", Proc. SPIE 8262, Gallium Nitride Materials and Devices VII, 826219 (27 February 2012);

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