Influence of Surface Roughness on the Optical Mode Profile of GaN-based Violet Ridge Waveguide Laser Diodes

摘要

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 10 nm 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.