J. Jedelský

Optically and thermally induced changes of structure, linear and non-linear optical properties of chalcogenides thin films

Abstract The spectral dependence of third-order non-linear susceptibilities, χ (3) , of amorphous As–S thin films was evaluated from changes of index of refraction using Miller’s rule. The exposure of thin fresh evaporated films and their annealing increases χ (3) , it increases also their homogeneity and level of their polymerization as can be judged from Raman spectra of the films. The large covalently bonded parts (‘molecules’) of the samples are apparently favorable for increase of χ (3) .

Pulsed laser deposition of pure and praseodymium-doped Ge–Ga–Se amorphous chalcogenide films

Abstract Pure and praseodymium-doped thin films of Ge30Ga5Se65 amorphous system were prepared by the pulsed laser deposition (PLD) technique. The composition of the prepared films was close to the composition of the used targets of bulk chalcogenide glass. The structure of the prepared films was also close to that of the targets as shown by the Raman spectra. The annealing of films shifted the position of the absorption edge to higher energies, which is explained by chemical homogenization of the films due to interaction of fragments of the evaporated material. Two luminescence bands near 1340 and 1610 nm were observed in the emission spectra of praseodymium-doped Ge–Ga–Se thin films. They were assigned to the radiative transitions between discrete energy levels of Pr3+ ions, 1G4–3H5 and 3F3–3H4, respectively. The luminescence intensity of ablated films was lower than that of bulk glasses. It increased after annealing of the films.

Thin amorphous chalcogenide films prepared by pulsed laser deposition

Abstract Amorphous Ge–Ga–Se thin films were prepared by pulsed-laser deposition (PLD), using different energy densities of the excimer KrF laser beam (λ=248 nm) on the glassy target. The chemical composition of prepared films was close to the composition of the chalcogenide glass targets. The structure of Ge–Ga–Se thin films was studied by Raman spectroscopy; GeSe4/2 tetrahedra, edge-sharing Ge2Se8/2 bi-tetrahedra, some Ge–Ge and Ge–Ga or Ga–Ga as well as Se–Se structural units were revealed. The optical properties (transmittance spectra, spectral dependence of index of refraction, optical gap, single oscillator energy, dispersion energy, dielectric constant) of the films were determined. The relations between the structure, optical parameters and energy density of the laser beam used for PLD are discussed.

On the optical properties of amorphous Ge–Ga–Se films prepared by pulsed laser deposition

Abstract Amorphous Ge–Ga–Se thin films (pure and dysprosium doped) were prepared by the pulsed laser deposition technique using different energy of the laser beam pulses. The effects of exposure and thermal annealing below the glass transition temperature on the optical parameters (index of refraction, optical band gap) and the thickness of as-deposited chalcogenide thin films were studied. The optical band gap and the thickness of the thin films increased with exposure of the films and even more with the annealing. Index of refraction has an opposite tendency. Two emission bands with maxima near 1140 and 1340 nm corresponding to 6F9/2, 6H7/2–6H15/2 and 6F11/2, 6H9/2–6H15/2 electron transitions of Dy3+ ions were identified in luminescence spectra of dysprosium doped thin films.

On the effect of composition on the Judd-Ofelt parameters of Sm3+-doped chalcogenide glasses

Abstract The GexGa5Se95−x glasses, where x=15, 17.5, 20, 22.5, 25, 27.5, 29.17, and 30, all doped with 1 wt% of samarium were prepared and studied. The compositional dependences of Judd–Ofelt intensity parameters of Sm3+ ions in studied glasses were evaluated and discussed in relation with the structure, bond covalency, bulk properties, and rigidity of the glassy matrix.

Expression of the optical constants of chalcogenide thin films using the new parameterization dispersion model

In this paper, a new dispersion model of the optical constants of amorphous solids enabling us to perform an efficient parameterization of the spectral dependences of the optical constants of chalcogenide thin films will be presented. This dispersion model is based on mathematical modeling the density of electronic states (DOS) corresponding to both the valence and conduction bands. The imaginary part of the dielectric function is then calculated by the numerical convolution of the DOS. The real part of the dielectric function is calculated using the corresponding Kramers-Kronig (KK) relation in a suitable numerical way. Moreover, the existence of the transitions between the localized states inside the band gap and the extended states inside both the valence and conduction bands is also taken into account using the corresponding convolutions. Thus, the dispersion model presented includes the absorption corresponding to the Urbach and Tauc regions. Then the dispersion model described allows to interpret spectroellipsometric and spectrophotometric data measured for the chalcogenide thin films within the wide spectral region (200-900 nm).

Optical characterization of chalcogenide thin films

Abstract In this paper, the optical characterization of a film of amorphous As–S chalcogenides evaporated on glass substrates will be performed using variable angle of incidence spectroscopic ellipsometry (VASE) and near-normal incidence spectroscopic reflectometry (NNSR). The spectral dependences of the ellipsometric parameters and reflectance of the chalcogenide thin film mentioned is measured within the near-UV, visible and near-IR spectral regions. For interpreting these optical quantities the new dispersion model of the spectral dependences of the optical constants of amorphous solids is employed. This model is based on the modified Lorentz oscillator. Within this model the concepts of the band gap and Urbach tail are respected.

Amorphous Ge–Se thin films prepared by pulsed-laser deposition

Amorphous Ge x Se1− x , x = 0.22–0.28 thin films were prepared by the pulsed-laser deposition technique. The photo-induced and thermally induced changes of structure and optical gap of the films were studied and discussed. The exposure and annealing causes bleaching of the films, and increases. The structure is influenced only a little by exposure; the annealing causes a decrease in the Raman band amplitudes corresponding to Ge–Ge and Se–Se bonds and to structural units similar to (GeSe) n . This can be ascribed to chemical reactions between fragments formed during pulsed-laser deposition.

Thermally and photoinduced changes of structure and optical properties of As-Ga-S amorphous films and glasses

Abstract New high purity glasses in the As 42 S 58 -Ga 42 S 58 and As 40 S 60 -Ga 40 S 60 systems were synthesised and the solubility regions of Ga 42 S 58 and Ga 40 S 60 in the As-S matrix were determined. Illumination of glassy powders and thin films shifts the short wavelength absorption edge, changes the optical gap, E g opt and changes their index of refraction, n . The sensitivity of Ga-containing films is higher than pure As-S. Annealing and illumination also changes the thickness of thin films, their density, the single oscillator energy, E o , dispersion energy, E d , of the Wemple-DiDomenico dispersion relationship and their Raman spectra. The changes in the Raman spectra are interpreted as photoinduced changes of short-range order in the structure of thin films. A microscopic model of the photoinduced changes is proposed.

Dysprosium-doped chalcogenide films prepared by pulsed-laser deposition

The chalcogenide glasses possess interesting optical properties such as a good transmission in the nIR-mIR wavelength region, high linear and non-linear refractive index and photosensitivity, which allows holographic patterns writing. Moreover, their low-phonon energy makes them good candidates for optical amplification. In order to design an integrated circuit on chalcogenide glasses, the pulsed laser deposition (PLD) technique is a suitable method for deposition of glass with complex composition. Amorphous Ge-Ga-Sb-S films (pure and dysprosium doped) were prepared by PLD using different energy of the laser beam pulses. Compositional, morphological and structural characteristics of the films were studied by MEB-EDS, atomic force, scanning electron microscopy, X-ray diffraction and Raman spectroscopy analyses. The photo-luminescence of Dy doped Ge-Ga-Sb-S films was investigated. The emission band centered at 1340 nm corresponding to 6F11/2, 6H9/2-6H15/2 electron transitions of Dy3+ ions was identified in luminescence spectra of dysprosium doped thin films. A study of the optical properties and the effects of exposure and thermal annealing below the glass transition temperature on the optical parameters of thin films from the Ge-Ga-Sb-S system will be presented.