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

Silicon carbide epilayers of cubic (3C) and hexagonal (4H and 6H) poly types were investigated by Auger electron spectroscopy, high-resolutio n electron energy-loss spectroscopy and Raman spectroscopy to determin e the excitation energies of the optical Fuchs-Kliewer surface phonons and their relation to hulk phonon frequencies. The surfaces were trea ted in a buffered hydrofluoric acid solution. Loss structures attribut ed to excitation of Fuchs-Kliewer phonons were clearly resolved. Their energies were found at 115.9 +/- 1 meV irrespective of the SiC polyty pe. The experimental data agree with values calculated from the experi mental bulk phonon frequencies and tabulated dielectric constants.