J. Orava

Optical properties and phase change transition in Ge2Sb2Te5 flash evaporated thin films studied by temperature dependent spectroscopic ellipsometry

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 amorph...

Optical properties of As33S67−xSex bulk glasses studied by spectroscopic ellipsometry

Variable angle spectroscopic ellipsometry (VASE) was employed to study the optical properties of As33S67−xSex (x=0, 17, 33.5, 50, and 67at.%) bulk glasses in the UV-vis-NIR (near infrared) spectral region for photon energies from 0.54to4.13eV (photon wavelengths from 2300to300nm). For data analysis, we employed Tauc–Lorentz (TL) dispersion model in the entire measured near bandgap spectral region and standard Cauchy dispersion model in the spectral region below the bandgap. With increasing Se content (x) in the bulk glass, we observed a linear decrease in optical bandgap energy Egopt from 2.52±0.02eV for As33S67 to 1.75±0.01eV for As33Se67 and linear increase in refractive index nTL in the NIR spectral region, e.g., at 0.80eV from 2.327 for As33S67 to 2.758 for As33Se67. The amplitude A decreased with increasing Se content. The peak transition energy E0 and broadening C had a maximum value for x=33.5at.% and systematically decreased for higher S or Se content in glasses. Our study showed that TL model is ...

The optical properties of chalcogenide glasses: From measurement to electromagnetic simulation tools

Chalcogenide glasses are promising candidate materials for a wide range of photonics applications. The design and realisation of optical components based on these materials requires detailed information on their optical properties, frequently over a range of wavelengths. In this paper we review experimental refractive index data for three chalcogenide glass compositions, and discuss how various numerical fits to the data prove useful within electromagnetic simulation tools.

Soft x-ray induced Ag diffusion in amorphous pulse laser deposited As50Se50 thin films: An x-ray photoelectron and secondary ion mass spectroscopy study

In the present paper, x-ray photoelectron spectroscopy (XPS) is used to induce and study the Ag diffusion and dissolution in pulsed laser deposited As50Se50 amorphous chalcogenide films. Dynamic secondary ion mass spectroscopy (SIMS) is also employed to investigate the Ag atomic concentration in depth. Dynamic SIMS measurements reveal that even before x-ray irradiation a considerable percentage of the total silver amount diffuses into the matrix forming an ∼70 nm mixed Ag–Se–As layer. XPS analysis shows that x-ray irradiation induces further diffusion of silver into the chalcogenide matrix. At the end of the procedure silver is found to be homogeneously dissolved into the matrix leaving only a 5–7 nm thick surface layer with excess silver concentration. In this surface layer stable Ag2Se clusters existing probably in quasicrystalline form prohibit further diffusion. The origin of the mechanism of the x-ray induced Ag diffusion and dissolution in amorphous chalcogenides is discussed in light of the present...