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.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
L. Redaelli ; M. Martens ; J. Piprek ; H. Wenzel ; C. Netzel, et al.
"Effect of ridge waveguide etch depth on laser threshold of InGaN MQW laser diodes", Proc. SPIE 8262, Gallium Nitride Materials and Devices VII, 826219 (February 9, 2012); doi:10.1117/12.908368; http://dx.doi.org/10.1117/12.908368