Raman Spectroscopic Stress Evaluation of Femtosecond-Laser-Modified Region Inside 4H-SiC

A femtosecond (fs)-laser-modified region inside single-crystal silicon carbide was studied by micro-Raman spectroscopy. Higher and lower peak energy shifts of the transverse optical (TO) phonon mode, which correspond to compressive and tensile stresses, were observed. Mappings of peak energies and spectral widths of the TO phonon mode showed a clear correspondence with the distributions of strained layers observed by transmission electron microscopy. The maximum compressive and tensile stresses were estimated to be 1.4 and 0.4 GPa, respectively. This result indicates that the periodic strained layers contain many nano-voids which are formed by nano-explosions induced by fs laser irradiation.