Formation of femtosecond laser-induced periodic nanostructures on GaN

The femtosecond laser-induced periodic surface structure (LIPSS) method has attracted considerable interest as a way to form fine structures with dimensions below the laser wavelength. These structures are highly reproducible, demonstrating that this method is suitable for applications such as quantum devices. In this study, we investigated the shape and crystalline state of a LIPSS to clarify the material properties and laser conditions that define its structure. While a LIPSS composed of GaN maintained its crystallinity, disturbances in its local crystalline orientation were generated. The direction and periodicity of the LIPSS did not depend on the in-plane crystal direction of GaN or the scanning direction, but the aspect ratio of each LIPSS depended on the in-plane crystal direction. The LIPSS with exposed {1-100}_GaN faces showed high aspect ratios, with narrower widths and deeper depths, than LIPSS with different exposed faces.