A variable angle of incidence spectroscopic ellipsometer equipped with a compensator has been used to determine the dielectric functions in the 0.74 - 6 eV photon energy range of n-type bulk 4H-SiC with doping concentrations between 10(17) and 10(19) cm(-3). The resulting dielectric function for different SiC wafers depends on the doping concentration, especially around the absorption onset and higher photon energies. Measurements on different wafers with the same doping show good reproducibility. Simulations and preliminary measurements show that ellipsometry might be useful for thickness determination of thin (<1 m) homoepitaxial films.

We report ordinary (??c axis) and extraordinary (??c axis) dielectric function data of 4H- and 6H-SiC from 3.5 to 9.0 eV. These data, which were obtained by with spectroscopic ellipsometry, are also compared to recently reported ab initio calculations. Critical point energies were found using real and reciprocal space analysis. © 2001 American Institute of Physics.

The optical band gap energy and the dielectric functions of n-type 4H-SiC have been investigated experimentally by transmission spectroscopy and spectroscopic ellipsometry and theoretically by an ab initio full-potential linear muffin-tin-orbital method. We present the real and imaginary parts of the dielectric functions, resolved into the transverse and longitudinal photon moment a, and we show that the anisotropy is small in 4H-SiC. The measurements and the calculations fall closely together in a wide range of energies. © 2002 American Institute of Physics.

Measurements of the dielectric function components parallel and perpendicular to the optical axis of wurtzite GaN are presented. The results are obtained on a multilayer AlxGa1-xN / GaN film grown on gamma -LiAlO2 which exhibits a very small amount of Al (x<0.1) in the uppermost layer. We use the spectroscopic ellipsometry to determine (omega) around the interband critical points of GaN up to 9 eV. Since the optical axis of the films are parallel to the surface, a separation of the different epsilon components is possible. The line shape of the measured tensor components e(parallel to) and epsilon (perpendicular to) is in very good agreement with results of recently published band-structure calculations. By comparison with the calculations we assign structures in the dielectric function to critical points in the Brillouin zone. In addition, a comparison with similar spectra for CdS and CdSe is presented, together with a discussion of possible spin-orbit splitting effects.