Dielectric functions of bulk 4H and 6H SiC and spectroscopic ellipsometry studies of thin SiC films on Si

Abstract

Spectroscopic rotating-analyzer ellipsometry employing a compensator and optical transmission were used to measure the dielectric functions of bulk 4H and 6H SiC from 0.72 to 6.6 eV for light propagating nearly parallel to the hexagonal axis. The measurements below the band gap show the presence of a thin surface layer, which was modeled as SiO2. The data are similar to results for cubic (3C) and 6H SiC from the literature, but differences are notable, particularly above 4 eV. At 5.56 eV, we observe a critical point in 4H SiC, which is assigned to direct interband transitions along the U=M−L axis in the hexagonal Brillouin zone after comparison with band structure calculations. No evidence for direct transitions below 6.5 eV was found in 6H SiC. We apply our results to the analysis of a 4H SiC film on insulator (SiCOI) produced by high-dose hydrogen implantation and direct wafer bonding on Si. For comparison, we also studied a 1 μm thick epitaxial layer of 3C SiC on Si, where the interference oscillations are influenced by surface and interface roughness.