Waveguiding in InGaN/GaN/AlGaN blue laser structures

Symmetric InGaN/GaN/AlGaN conventional blue laser waveguides are analyzed. It is shown that due to the limited thickness of the confinement layers, the confinement factor in the active region and the modal absorption are considerably influenced by the substrate and GaN buffer layers. These phenomena are due to the coupling of the light outside of the active region in the substrate and buffer layers and show resonances with respect to the thickness of the buffer layer. These effects may strongly affect the gain, the near-field and the far-field of the lasing mode, specially if the substrate is SiC or GaN. In order to optimize the laser waveguide an alternative structure is proposed with a few microns thick AlGaN buffer layer instead of the usual GaN buffer layer. We also propose to use asymmetric structures where the extension of the optical field is minimized in the p-side and extended in the n-regions.