Formation of periodic strained layers associated with nanovoids inside a silicon carbide single crystal induced by femtosecond laser irradiation

We observed the formation of subwavelength periodic strained layers associated with nanovoids in the cross section of femtosecond laser-irradiated lines written inside 4H-SiC single crystals. Both conventional and high-voltage transmission electron microscopies were carried out for microstructural analyses. The cross section of the irradiated lines consists of four to six groups of fine periodic structures. Each group is composed of strained layers with a typical spacing of 150 or 300 nm. The layers extend along the irradiated lines, aligned parallel to the electric field of the laser light. Tiny voids approximately 20 nm in diameter are found in the layers.