Influence of surface roughness on the optical mode profile of GaN-based violet ridge waveguide laser diodes

We investigate the influence of the epitaxial layer roughness on the far-field profile of the optical mode in gallium nitride-based, c-plane ridge waveguide laser diodes. Occasionally, we observe long-range growth instabilities leading to a periodical modulation of the surface. Amplitude and period of this surface roughness is typically on the order of a few 10nm and 20 µm, respectively. Using different characterization techniques, we investigate the influence of the surface roughness on the vertical mode profile along the fast axis in the far-field, in particular the contribution of light scattering at the rough waveguide interfaces, as well as that of substrate modes.