Fabrication of periodic nano-hole array on GaN surface by fs laser for improvement of extraction efficiency in blue LED

For micro/nanofabrication of Gallium nitride (GaN), we developed wet-chemical-assisted femtosecond-laser ablation method. Obtained ablation craters exhibit higher quality and better uniformity without residual debris compared with those produced by femtosecond-laser ablation in air followed by etching. Multi-scan irradiation was performed to fabricate periodic structure composed of high aspect ratio nano-holes using the wet-chemical-assisted ablation method. The aspect ratio is much improved (∼1.6) compared to the case of using single pulse irradiation. This periodic structure of uniform nano-holls arranged on GaN surface can act as a two-dimensional photonic crystal which is expected to enhance a light extraction efficiency of blue LED.