Processing grating structures on surfaces of wide-bandgap semiconductors using femtosecond laser and phase mask

Fabrication of grating structures on surfaces of wide-bandgap semiconductors, namely silicon carbide (SiC) and gallium nitride (GaN), was achieved using a femtosecond laser and a phase mask. The phase mask was used to produce stable interference patterns from the focused femtosecond laser to form the grating structures on the bulk materials. The effects of the irradiation power and time on the Bragg grating morphology that was formed on the SiC surface were studied. By optimizing the fabrication parameters, we successfully produced grating structures with uniform periods of 1.07μm1.07  μm on SiC and GaN. The threshold powers necessary for grating structure formation on wide-bandgap semiconductors were investigated. It was found that the threshold powers for SiC and GaN were much smaller than those for silica glass. The reason for this difference is that the absorption of the incident laser light in SiC and GaN is a lower-order nonlinear absorption process compared to that in silica glass.