Ellipsometric studies of SiC in the infrared, visual and ultraviolet spectral region

Sammanfattning: Spectroscopic ellipsometry has been used to determine the dielectric function of the most common polytypes, 3C, 4H and 6H, of SiC and also of some related materials. Measurements have been performed in the infrared, visible and ultraviolet energy region. Effects such as surface roughness, crystal anisotropy, free-charge carrier concentrations, and phonon modes are discussed. For the measurements in the infrared region a Fourier transform rotating compensator ellipsometer working in the 300-8000 cm-1 wave number region has been used. The result provides an accurate determination of the dielectric function for the uniaxial structure; several phonon modes not observed with ellipsometry before but expected from Raman spectroscopy are detected. Additionally, the modeling and subsequent fitting enables determination of the effective masses and free carrier concentrations, in good agreement with result obtained by other techniques. For the visible and ultra-violet photon energy region, the results provide imminent feedback for the theoretical calculations regarding the band-to-band transitions. Measurements for energies up 9 eV have been made using a N2-purged environment and MgF optics. The results are analyzed using both real and reciprocal space analysis and critical point energies are determined.Samples measured had free carrier concentrations in the 1017 to 1019 cm-3 range. Both single side and double side polished samples and samples with additional oxide were studied. Sample cleaning was also addressed. Additionally, some results on 3C-SiC grown on silicon are included.