Far-IR characterization of GaInAs/InP quantum wells and superlattices

We used far-IR reflectance spectra to characterize a series of Ga0.53In0.47As/InP multiple quantum well and superlattices grown by metal-organic vapour phase epitaxy on InP:S substrates, with well widths ranging from 10 to 92 Å and barriers from 7 to 135 Å. We obtained good fitting to the experimental spectra by taking into account the complex dielectric functions of the quantum structures, in the effective-medium approximation, and using the transfer matrix formalism. The thicknesses of wells and barriers were determined from the fit, and the values of energies and broadening of phonon modes

I Greci nel sud dell'Italia

Capitoli redatti: "La prassi urbanistica", "Le architetture e le funzioni", "Originalità delle produzioni artistiche", "I documenti di una società di tipo aristocratico

Photoreflectance Characterization of InGaAs Lattice Matched to InP

We measured photoreflectance (PR) spectra at different temperatures between 80 and 300 K, and optical absorption (OA) at 3 K on MOVPE grown Inl-xGaxAs nearly lattice-matched to InP. x-ray diffraction measurements gave a lattice mismatch δa/ao = -0.9.10−3 between ternary alloy and InP, corresponding to × = 0.485. We obtained the energy gap dependence on T from PR spectra. The blue shift of the gap was accounted for in terms of compositional difference with respect to the perfectly lattice matched alloy (× = 0.472), and elastic strain; moreover PR and OA showed evidence of the valence bands splitting at k = 0 due to interfacial strain, in fine agreement with theory

OPTICAL STUDY OF NIOBIUM DISILICIDE POLYCRYSTALLINE FILMS

NbSi2 polycrystalline films, coevaporated and thermally annealed, were subjected to chemical and structural characterization, and then studied by reflectance from 0.06 to 6 eV and ellipsometry from 1.4 to 5 eV. The dielectric functions, obtained from Kramers-Kronig analysis and directly from ellipsometry, are also presented. Low-frequency free-carrier response is discussed in terms of the Drude model; the high-frequency interband structures are interpreted on the basis of the calculated density of states and photoemission results. A comparison is made with the optical properties of isoelectronic VSi2 and TaSi2 Polycrystalline films

Far-infrared spectroscopy of thermally annealed tungsten silicide films

The far-infrared transmittance spectrum of tungsten silicide has been observed for the first time. WSi2 polycrystalline films were prepared by coevaporation and chemical-vapour deposition on silicon wafers, and subsequently thermally annealed at different temperatures. The observed structures are interpreted, on the basis of the symmetry properties of the crystal, such as infrared-active vibrational modes. Moreover, the marked lineshape dependence on annealing temperature enables this technique to analyse the formation of the solid silicide phases