Low propagation loss in GaN/AlGaN-based ridge waveguides

We report the fabrication and characterization of GaN/AlGaN ridge waveguides (WG). The "ridge" design was chosen to ensure low propagation loss. The fabrication process included four steps that could be easily regulated. GaN and AlGaN cladding layers were grown on a sapphire substrate by MOCVD. Shallow ridges were formed in the top cladding layer using ICP-RIE. After etching, samples were diced and WG facets were formed by polishing the samples opposite sides. The propagation loss at 1.56 μm was evaluated by measuring Fabry-Perot resonances from end-facet reflections. Losses as low as 1 dB/cm were measured for single mode WGs. Such low-loss two-dimensional WG could advance the use of GaN in integrated optoelectronics wave guiding components. Schematic illustration of GaN ridge WG structure (left) and a SEM image of a 10 μm wide ridge WG structure (right).