Effect of ridge waveguide etch depth on laser threshold of InGaN MQW laser diodes
L. Redaelli1, M. Martens2, J. Piprek3, H. Wenzel1, C. Netzel1, A. Linke1, Y.V. Flores1, S. Einfeldt1, M. Kneissl1,2 and G. Tränkle1
Published in:
Proc. SPIE, vol. 8262, no. 826219 (2012).
Abstract:
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.
1 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, D-12489 Berlin, Germany
2 Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
3 NUSOD Institute LLC, Newark, Delaware 19714-7204, USA
Keywords:
InGaN laser diodes, threshold current density, ridge width, ridge depth, far field pattern, current spreading, index anti-guiding.
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