Diagnostic of the Metal-Dielectric Interface in a Collective Oscillation of Electrons

Light reflected from a dielectric- metal interface describe the existence of resonant modes of the collective oscillation in electron density. The experimental configuration proposed by Otto and Kretschmann- Raether can be used to characterizes the optical properties of thin metallic films in contact with a dielectric medium. In far-field detection, the angular dependence of the reflectivity on Ag/ ambient air shows a sharp minimum beyond attenuated total reflection. At a wavelength, λ the geometric parameters influence strongly the angular resonance θSP. In the case of Ag, λ = 633.0 nm, at the optimal thickness, d = 50.8nm, a resonant coupling is reaches between incident photons and free electrons in the angular range 45° < θSP < 46°. The angular resonance is associated with the optical phenomenon of an energetic transfer predicted theoretically.Light reflected from a dielectric- metal interface describe the existence of resonant modes of the collective oscillation in electron density. The experimental configuration proposed by Otto and Kretschmann- Raether can be used to characterizes the optical properties of thin metallic films in contact with a dielectric medium. In far-field detection, the angular dependence of the reflectivity on Ag/ ambient air shows a sharp minimum beyond attenuated total reflection. At a wavelength, λ the geometric parameters influence strongly the angular resonance θSP. In the case of Ag, λ = 633.0 nm, at the optimal thickness, d = 50.8nm, a resonant coupling is reaches between incident photons and free electrons in the angular range 45° < θSP < 46°. The angular resonance is associated with the optical phenomenon of an energetic transfer predicted theoretically

Adequate Method for Decoupling Bulk Lifetime and Surface Recombination Velocity in Silicon Wafers

In this paper, we present an appropriate method of decoupling surface and bulk recombination processes in silicon wafers. The study was carried out using the surface passivation of multicrystalline silicon wafers by ethanolic solution of iodine at different molarities varying between 0.01 M and 0.1 M. The effect of the concentration of ethanolic iodine solution on surface passivation effectiveness was investigated by using quasi steady state photoconductance technique. Reproducible experiments have shown that the best passivation is reached for a molarity of around 0.02 M. The carrier lifetime after passivation at 0.02 M has been improved by more than one order of magnitude, compared to that of the same wafer before the passivation. Using an adequate modeling of minority carrier lifetime curves τ (∆n), based on Hornbeck-Haynes model, surface recombination velocity was calculated. The minimum values of surface recombination velocity have been found to be approximately 120 cm/s for 0.02 M. The modeling results indicate that the minority carrier lifetime improvement can be easily correlated with the decrease of the surface recombination velocity for a fixed bulk lifetime τ b = 115 µs

Half-Metallic Ferromagnetism in Double Perovskite Ca2CoMoO6 Compound : DFT + U Calculations

A systematic investigation on magnetism and spin-resolved electronic properties in double perovskite Ca2CoMoO6 compound was performed by using the full-potential augmented plane wave plus local orbitals (APW+lo) method within the generalized gradient approximation (GGA-PBE) and GGA-PBE+U scheme. The stability of monoclinic phase (P2114) relative to the tetragonal (I487) and cubic (Fmm 225) phase is evaluated. We investigate the effect of Hubbard parameter Uon the ground-state structural and electronic properties of Ca2CoMoO6 compound. We found that the ferromagnetic ground state is the most stable magnetic configuration. The calculated spin-polarized band structures and densities of states indicate that the Ca2CoMoO6 compound is half-metallic (HM) and half-semiconductor (HSC) ferromagnetic (FM) semiconductor with a total magnetic moment of 6.0 using GGA-PBE and GGA-PBE+U, respectively. The Hubbard U parameter provides better description of the electronic structure. Using the Vampire code, an estimation of exchange couplings and magnetic Curie temperature is calculated. Further, our results regarding the magnetic properties of this compound reveal their ferromagnetic nature. The GGA-PBE+U approach provides better band gap results as compared to GGA-PBE approximation. These results imply that Ca2CoMoO6 could be a promising magnetic semiconductor for application in spintronic devices

BAs and boride III-V alloys

Boron arsenide, the typically-ignored member of the III-V arsenide series BAs-AlAs-GaAs-InAs is found to resemble silicon electronically: its Gamma conduction band minimum is p-like (Gamma_15), not s-like (Gamma_1c), it has an X_1c-like indirect band gap, and its bond charge is distributed almost equally on the two atoms in the unit cell, exhibiting nearly perfect covalency. The reasons for these are tracked down to the anomalously low atomic p orbital energy in the boron and to the unusually strong s-s repulsion in BAs relative to most other III-V compounds. We find unexpected valence band offsets of BAs with respect to GaAs and AlAs. The valence band maximum (VBM) of BAs is significantly higher than that of AlAs, despite the much smaller bond length of BAs, and the VBM of GaAs is only slightly higher than in BAs. These effects result from the unusually strong mixing of the cation and anion states at the VBM. For the BAs-GaAs alloys, we find (i) a relatively small (~3.5 eV) and composition-independent band gap bowing. This means that while addition of small amounts of nitrogen to GaAs lowers the gap, addition of small amounts of boron to GaAs raises the gap (ii) boron ``semi-localized'' states in the conduction band (similar to those in GaN-GaAs alloys), and (iii) bulk mixing enthalpies which are smaller than in GaN-GaAs alloys. The unique features of boride III-V alloys offer new opportunities in band gap engineering.Comment: 18 pages, 14 figures, 6 tables, 61 references. Accepted for publication in Phys. Rev. B. Scheduled to appear Oct. 15 200

Contribution to the study of electronic structure of crystalline semiconductors (Si, Ge, GaAs, Gap, ZnTe, ZnSe)

The band structure of semiconductors was described by several theorists since the Fifties. The main objective of the present paper is to do a comparative study between various families of semi-conductors IV (Si,Ge), III-V (GaAs, GaP) and II-VI (ZnSe, ZnTe) with both methods; tight Binding1 method and pseudo potential method2. This work enables us to understand as well as the mechanism of conduction process in these semiconductors and powers and limits of the above methods. The obtained results allow to conclude that both methods are in a good agreement to describe the morphology of band structures of the cited semiconductors. This encourages us to study in the future the electronic behaviour through the structure of bands for more complex systems such as the heterostructures

GEOMETRY OF WAVES GUIDES FOR CONTAINMENT OF PROPAGATING RESONANT MODES

<p>We are study de mode fundamental de 1D in the two media (MIM and IMI)  of a metallic structure (Ag) (silver) in which a small hole is perforated (as à dielectric  medium). We take the conditions that resonant modes (PPSs) are confined or the surface.Via the complex permittivity of the metal and those of the dielectric medium .The effective index n_effof the elaborated structure controlled remarkably the properties of the propagating modes. Of the structure playing he mode to guide SPP modes .Where the confinement follow the order in sub-wave length scale of the width hole in silver and limited by the attenuation length (skin depth).</p