SUBWAVELENGTH PERIODIC RIPPLE FORMATION ON GaN SURFACE BY FEMTOSECOND LASER PULSES

The formation of femtosecond pulsed laser-induced periodic surface structure on GaN is reported for the first time (to our knowledge) in this paper. It has been found that the formation of the laser-induced ripples is very much dependent and quite sensitive to the laser conditions of the incident laser beam energy fluence and pulse numbers. Possibly due to the unique property of high-defect density of GaN material, the process window for laser-induced ripple formation is quite narrow compared to other materials such as InP, GaP, Al2O3 etc. Nevertheless, through finely adjusting laser beam fluence and pulse number, subwavelength periodic ripples could be formed on the GaN surface. The formation of such periodic two-dimensional structures was attributed to optical interference of the incident laser light with scattered waves from a surface disturbance. Photoluminescence emission could still be detected on the GaN ripple area, indicating little degradation of GaN optical property after femtosecond laser processing. The femtosecond laser-induced ripple structure has potential applications in the fabrication of nanostructures for the GaN-based devices.