PHONONS IN 3C-SIC, 4H-SIC, AND 6H-SIC

Silicon carbide epilayers of cubic (3C) and hexagonal (4H and 6H) polytypes were investigated by Auger electron spectroscopy, high-resolution electron energy-loss spectroscopy and Raman spectroscopy to determine the excitation energies of the optical Fuchs-Kliewer surface phonons and their relation to hulk phonon frequencies. The surfaces were treated in a buffered hydrofluoric acid solution. Loss structures attributed to excitation of Fuchs-Kliewer phonons were clearly resolved. Their energies were found at 115.9 +/- 1 meV irrespective of the SiC polytype. The experimental data agree with values calculated from the experimental bulk phonon frequencies and tabulated dielectric constants.