The optical functions of ␤-Ga 2 O 3 thin films have been determined by ellipsometry from 0.74-5 eV. Several electron-beam evaporated and rf magnetron sputtered films of different thicknesses were investigated using a multisample technique. Refractive index values comparable to those of bulk material are found. Cauchy dispersion model fits yield a high-frequency dielectric constant ⑀ ϱ of 3.57. Above 4.7 eV a direct absorption edge is observed.

No abstract

Band structure calculations for β-FeSi2 have been performed by the linear muffin-tin orbital method within the local density approximation scheme including exchange and correlation effects. A detailed analysis of the conduction and valence band structure around high-symmetry points has shown the existence of a quasidirect band gap structure in the material. It is experimentally confirmed that between the threshold energy of optical interband transition of 0.73 eV and the first direct gap transition with appreciable oscillator strength at about 0.87 eV there is a region in which direct transition of low oscillator strength and indirect transitions overlap. That explains the tricky behavior of β-FeSi2 in experimental investigations demonstrating it to be either a direct or indirect gap semiconductor.

No abstract

No abstract

No abstract

We present both theoretical and experimental investigations of electronic and optical properties of isostructural ␤-FeSi 2 and OsSi 2 by means of a full-potential linear augmented plane wave method and optical measurements. We report also ellipsometric and reflectance measurements on samples of polycrystalline osmium disilicide prepared by mechanical alloying. From ab initio calculations these compounds are found to be indirect band-gap semiconductors with the fundamental gap of OsSi 2 larger some 0.3-0.4 eV than the one of ␤-FeSi 2 . In addition to that, a low value of the oscillator strength is predicted for the first direct transitions in both cases. Computed optical functions for these materials were compared to the ones deduced from optical measurements, indicating very good agreement and the presence of some anisotropic effects.Polycrystalline osmium disilicide has been grown by mechanical alloying. The annealed samples contained 0.5-wt. % PHYSICAL REVIEW B, VOLUME 64, 075208

No abstract