Investigation of removal mechanisms and conditions of GaN under ultrafast laser irradiation and their effects on surface micro/nano structures

GaN is characterized by high electron velocity, high electric field, and excellent thermal conductivity, making it highly relevant across various fields. In this study, an ultrafast laser with a pulse duration of 8 ps and a wavelength of 532 nm was used to explore GaN’s ablation characteristics and its underlying mechanisms. Five distinct structures were identified, including shallow incomplete ablation, deep incomplete ablation, complete ablation with edge breakage, substrate damage, and successful ablation, all of which were linked to specific ablation parameters. Two primary ablation mechanisms were observed: one at low laser fluence, where high decomposition pressure led to ablation, and another at high laser energy, where intense electromagnetic effects directly caused ablation. The main defects identified were stress cracking due to high decomposition pressure and substrate damage resulting from excessive laser energy. The threshold for stress cracking was approximately 0.01 J/cm², while substrate damage occurred at about 0.25 J/cm² and increased with the decreasing repetition frequency under the influence of spot overlap. By adjusting the laser parameters, different ablation mechanisms could be employed, enabling the fabrication of microgrooves focused on edge quality and substrate recovery that prioritized cleanliness. This study provides valuable insights into the interaction mechanisms between ultrafast lasers and GaN, offering a new theoretical foundation and practical guidance for achieving precise, low-carbon GaN micro/nano machining.