We studied the optical properties of as-prepared (amorphous) and thermally crystallized (fcc) flash evaporated Ge2Sb2Te5 thin films using variable angle spectroscopic ellipsometry in the photon energy range 0.54–4.13 eV. We employed Tauc–Lorentz (TL) model and Cody–Lorentz (CL) model for amorphous phase and TL model with one additional Gaussian oscillator for fcc phase data analysis. The amorphous phase has optical bandgap energy Egopt=0.65 eV (TL) or 0.63 eV (CL) slightly dependent on used model. The Urbach edge of amorphous thin film was found to be ∼70 meV. Both models behave very similarly and accurately fit to the experimental data at energies above 1 eV. The CL model is more accurate in describing dielectric function in the absorption onset region. The thickness decreases ∼7% toward fcc phase. The bandgap energy of fcc phase is significantly lower than amorphous phase, Egopt=0.53 eV. The temperature dependent ellipsometry revealed crystallization in the range 130–150 °C. The bandgap energy of amorphous phase possesses temperature redshift −0.57 meV/K (30–110 °C). The crystalline phase has more complex bandgap energy shift, first +0.62 meV/K (150–180 °C) followed by −0.29 meV/K (190–220 °C). The optical properties (refractive index, extinction coefficient, and optical bandgap energy) of as-prepared and fcc flash evaporated Ge2Sb2Te5 thin films are very similar to those values previously reported for sputtered thin films.

The optical spectra of silicon are studied ellipsometrically at temperatures between 300 and 1200 K in the spectral range from 2 to 4.3 eV. We present a database of optical constants for pure and heavily doped samples, with the highest concentration of free carriers of 4ϫ10 20 cm Ϫ3 . We cover the photon energy range between 0.2 and 2 eV by using an oscillator representation of the visible and ultraviolet ellipsometric data. We also report the results for the temperature dependence of the E 1 interband transition. The values of the energy shift and Lorentzian broadening of this spectral feature are obtained from analytical critical-point line shapes by fitting differentiated dielectric functions; alternatively, we apply the numerical convolution with Lorentzian contours to describe quantitatively the increased broadening with increasing temperature.

We study the optical properties of tensile strained GaAs1−yNy (0%⩽y⩽3.7%) single layers for photon energies from 0.75 to 4.5 eV and for wave numbers from 100 to 600 cm−1 using spectroscopic ellipsometry. The intentionally undoped GaAsN layers were grown pseudomorphically on top of undoped GaAs buffer layers deposited on Te-doped (001) GaAs substrates by metalorganic vapor phase epitaxy. We provide parametric model functions for the dielectric function spectra of GaAsN for both spectral ranges studied here. The model functions for photon energies from 0.75 to 4.5 eV excellently match dielectric function data obtained from a numerical wavelength-by-wavelength inversion of the experimental data (point-by-point fit). Critical-point analysis of the point-by-point fitted dielectric function is performed in the spectral regions of the fundamental band gap and the critical-point transitions E1 and E1+Δ1. The band-gap energy is redshifted whereas the E1 and E1+Δ1 transition energies are blueshifted with increasing y. For y⩽1.65% the observed blueshift of the E1 energy is well explained by the sum of the effects of biaxial (001) strain and alloying. The GaAsN layers show a two-mode phonon behavior in the spectral range from 100 to 600 cm−1. We detect the transverse GaAs- and GaN-sublattice phonon modes at wave numbers of about 267 and 470 cm−1, respectively. The oscillator strength of the GaN-sublattice resonance increases linearly due to alloying and tensile strain. We compare our results from the single layers with those obtained previously from tensile and compressively strained GaAsN/GaAs and GaAsN/InAs/GaAs superlattices.

The effects of the nitrogen concentrations on the E1 and E1+Δ1 transitions of tensile-strained GaAs1−yNy (0.1%⩽y⩽3.7%) grown pseudomorphically to GaAs by metalorganic vapor-phase epitaxy are studied by spectroscopic ellipsometry. Adachi’s critical-point composite model is employed for ellipsometry data analysis. Contrary to the well-known redshift of the band-gap energy E0, we observe linearly blueshifted E1 and E1+Δ1 transition energies with increasing nitrogen composition y. For nitrogen compositions of 0⩽y⩽1.65%, the observed blueshift of the E1 energy is well explained by the sum of the effects of biaxial (001) strain and alloying.

The optical properties of silicon have been determined from 0.2 to 6.5 eV at room temperature, using reflectance spectra of silicon-on-insulator (SOI) and ellipsometric spectra of homoepitaxial samples. Optimized Fabry-Perot-type SOI resonators exhibit high finesse even in near ultraviolet. Very high precision values of the real part of the refractive index are obtained in infrared up to a photon energy of 1.3 eV. The spectra of the extinction coefficient, based on observations of light attenuation, extend to 3.2 eV due to measurements on SOI layers as thin as 87 nm. These results allowed us to correct spectroellipsometric data on homoepitaxial samples for the presence of reduced and stabilized surface layers.