Simulation and optimization of 420 nm InGaN/GaN laser diodes

Using self-consistent laser simulation, we analyze the performance of nitride Fabry-Perot laser diodes grown on sapphire. The active region contains three 4 nm InGaN quantum wells. It is sandwiched between GaN separate confinement layers and superlattice AlGaN/GaN cladding layers. AlGaN is used as an electron barrier layer. Pulsed lasing is measured near 420 nm wavelength and at temperatures up to 120 degreesC. Advanced laser simulation is applied to link microscopic device physics to measurable device performance. Our two-dimensional laser model considers carrier drift and diffusion including thermionic emission at hetero-boundaries. The local optical gain is calculated from the wurtzite band structure employing a non-Lorentzian line broadening model. All material parameters used in the model are evaluated based on recent literature values as well as our own experimental data. Simulation results are in good agreement with measurements. Multi-lateral mode lasing is calculated with a high order vertical mode. The carrier distribution among quantum wells is found to be strongly non-uniform leading to a parasitic (absorbing) quantum well. The influence of defect recombination, vertical carrier leakage and lateral current spreading is investigated. The reduction of such carrier losses is important to achieve lower threshold currents and less self-heating. Several device optimization options are proposed. Elimination of the parasitic quantum well is shown to substantially enhance the device performance.