Nitrogen In The Amorphous-germanium Network: From High Dilution To The Alloy Phase

In this work experimental data referring to the structural and optoelectronic characteristics of amorphous-germanium-nitrogen thin films are presented and discussed. The nitrogen content of the a-Ge:N samples, deposited by the rf-sputtering technique in an Ar+N2 atmosphere, was allowed to vary from typical impurity levels (less than 0.5 at. %) up to around 35 at. %. The material properties change depending on the nitrogen concentration, determined from a deuteron-induced nuclear reaction. The likely mechanisms of nitrogen incorporation into the solid phase are discussed, as well as the influence of the nitrogen content on the transport and optical properties of the films. A proportionality constant relating the total nitrogen concentration in the solid phase and the integrated absorption of the in-plane stretching vibration mode of the Ge-N dipole has been determined. It has been found that a close analogy exists between the general properties of a-Ge:N alloys and those measured in amorphous-silicon-nitrogen alloys. © 1993 The American Physical Society.4874560457

Raman spectroscopy of lithium niobate (LiNbO3) − Sample temperature and laser spot size effects

The Raman spectrum of lithium niobate (LiNbO3) was investigated in the 83–823 K temperature range and as a function of different laser spot sizes. The measurements considered a Z-cut (congruent, undoped) LiNbO3 crystal, HeNe laser excitation (632.8 nm photons), and the zx,xyz¯ geometry. The main LiNbO3-related phonon modes were identified and analyzed in terms of their peak position (ω) and linewidth (γ), according to which it was possible to identify the contributions originating from anharmonic phonon-coupling and thermal lattice-expansion processes. The analyses of the temperature-dependent ωT and γT data took into account the 3- and 4-phonon model and the experimental Grüneisen and linear thermal expansion coefficients − as available from literature. Among all phonon modes of LiNbO3, the A1(TO4) mode presented a peculiar behavior (at room temperature) that depends on the laser spot size during the Raman measurements. The development of this forbidden mode has been associated with the congruent-photorefractive nature of LiNbO3 as well as with small variations in the geometry of polarization (as a result of changes in the laser spot size)

The optical bandgap of lithium niobate (LiNbO3) and its dependence with temperature

Notwithstanding the great scientific−technological interest in lithium niobate (LiNbO3), its optical bandgap Egap has been subject of intense discussion. So far, the literature exhibits different Egap values spanning over about 2 eV and comprises a mixture of compositions, structures, and theoretical methods − not always clearly indicated or discussed. In view of that, this work presents a thorough investigation of the Egap (at room-temperature and in the ∼80–800 K temperature range) of the congruent ferroelectric LiNbO3 (Z-cut) single crystal

Local Electronegativity And Chemical Shift In Si And Ge Based Molecules And Alloys

The present work discusses the correspondence existing between the chemical shift induced by a foreign atom in the core levels of Si and Ge and the impurity's electronegativity. To this aim, gaseous and solid Si and Ge based molecules and alloys with different atomic constituents were investigated. The chemical shifts of the Si 2p and of the Ge 3d core levels, as determined by X-ray Photoelectron Spectroscopy (XPS), are shown to be proportional to the local electronegativity (according to Sanderson's scale). The chemical shift per bond has been also investigated in terms of the charge transferred between host and foreign atoms. The possibility of a new electronegativity scale based on electron charge transfer is discussed. © 1995.954207210Pauling, (1960) The Nature of Chemical Bonds, , 3rd Edition, Cornell University Press, New YorkMulliken, (1949) J. Chem. Phys., 46, p. 497Gordy, (1946) J. Chem. Phys., 14, p. 305Allred, Rochow, (1958) J. Inorg. Nucl. Chem., 5, p. 264Phillips, (1973) Bonds and Bands in Semiconductors, , Academic PressSanderson, (1976) Chemical Bonds and Bond Energy, , Academic Press, New York, Chap. 5Pritchard, Skinner, (1955) Chem. Rev., 55, p. 745Lucovsky, (1979) Sol. State Commun., 29, p. 571. , See, for exampleCardona, Ley, Photoemission in Solids I (1978) General Principles, , M Cardona, L Ley, Springer-Verlag, Berlin, Chap. 1Briggs, Seah, (1984) Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, , John Wiley & SonsBakke, Chen, Jolly, (1980) J. Electron Spectr. & Rel. Phen., 20, p. 333. , and references thereinHenderson, Physical Chemistry — An Advanced Treatise (1970) Molecular Properties, 4. , Academic Press, Chap. 11Gelius, Heden, Hedman, Lindberg, Manne, Nordberg, Nordling, Siegbahn, Molecular Spectroscopy by Means of ESCA III. Carbon compounds (1970) Physica Scripta, 2, p. 70Perry, Jolly, (1974) Inorg. Chem., 13, p. 1211Ley, (1984) The Physics of Hydrogenated Amorphous Silicon II, , See, for example, J.D Joannopoulos, G Lucovsky, Springer-Verlag, chap.

Erbium Luminescence In A-si:h

We have prepared a-Si:H with erbium impurities by co-sputtering. Efficient photoluminescence at 1.54 μm was observed in as-deposited samples. The maximum luminescence efficiency, 17, was found for an Er/Si concentration ∼ 2 at.% in samples prepared under low cathode bias. These samples have columnar structure and have ∼ 3 at.% O/Si. Annealing under oxygen atmosphere at 300°C can increase 17 at room temperature by a factor 3 and η at 77 K by a factor 5. The optimum erbium concentration is two orders of magnitude larger than in ion implanted crystalline silicon or in glasses. Hydrogen concentration is a fundamental parameter to obtain efficient luminescence. This material is a good candidate for Er3+ based photonic devices. © 1998 Elsevier Science B.V. All rights reserved.227-230PART 1399402Green P.E., Jr., (1996) IEEE J. Selected Areas Commun., 14, p. 764Rare earth doped semiconductors (1994) Mater. Res. Soc. Symp. Proc., p. 316Rare earth doped semiconductors II (1996) Mater. Res. Soc. Symp. Proc., p. 422Polman, A., (1997) J. Appl. Phys., 82, p. 1Priolo, F., Franzò, G., Coffa, S., Polman, A., Libertino, S., Barklie, R., Carey, D., (1995) J. Appl. Phys., 78, p. 3874. , and references thereinShin, J.H., Serna, R., Van Den Hoven, G.N., Polman, A., Van Sark, W.G.J.H.M., Vredenberg, A.M., (1996) Appl. Phys. Lett., 68, p. 997Oestereich, T., Swiatowski, C., Broser, I., (1990) Appl. Phys. Lett., 56, p. 446Bressler, M.S., Gusev, O.B., Kudoyarova, V.Kh., Kuznetsov, A.N., Pak, P.E., Terukov, E.I., Yassievich, I.N., Sturm, A., (1995) Appl. Phys. Lett., 67, p. 3599Zanatta, A.R., Nunes, L.A.O., Tessler, L.R., (1997) Appl. Phys. Lett., 70, p. 511Przybylinska, H., Jantsch, W., Suprun-Belevitch, Y., Stepikhova, M., Palmetshofer, L., Hendorfer, G., Kozanecki, A., Sealy, B.J., (1996) Phys. Rev. B, 54, p. 2532Van Den Hoven, G.N., Shin, J.H., Polman, A., Lombardo, S., Campisano, S.U., (1995) J. Appl. Phys., 78, p. 2642Eaglesham, D.J., Michel, J., Fitzgerald, E.A., Jacobson, D.C., Poate, J.M., Benton, J.L., Polman, A., Kimerlingh, L.C., (1991) Appl. Phys. Lett., 48, p. 2797Miniscalco, W.J., (1991) J. Lightwave Technol., 9, p. 234Street, R.A., (1991) Hydrogenated Amorphous Silicon, , Cambridge Univ. Press, Cambridg

On The Doping Efficiency Of Nitrogen In Hydrogenated Amorphous Germanium

This letter reports on the doping efficiency of nitrogen in a-Ge:H films of electronic quality. It has been found that nitrogen is an effective dopant in the a-Ge:H network, its doping efficiency being similar to the one corresponding to phosphorus in a-Si:H. The concentration of active nitrogen atoms decreases with impurity content following a square root dependence on total nitrogen. This behavior is similar to the one determined for column V dopants in a-Si:H films of electronic quality.621586

Nitrogen In Germanium

The known properties of nitrogen as an impurity in, and as an alloy element of, the germanium network are reviewed in this article. Amorphous and crystalline germanium-nitrogen alloys are interesting materials with potential applications for protective coatings and window layers for solar conversion devices. They may also act as effective diffusion masks for III-V electronic devices. The existing data are compared with similar properties of other group IV nitrides, in particular with silicon nitride. To a certain extent, the general picture mirrors the one found in Si-N systems, as expected from the similar valence structure of both elemental semiconductors. However, important differences appear in the deposition methods and alloy composition, the optical properties of as grown films, and the electrical behavior of nitrogen-doped amorphous layers. Structural studies are reviewed, including band structure calculations and the energies of nitrogen-related defects, which are compared with experimental data. Many important aspects of the electronic structure of Ge-N alloys are not yet completely understood and deserve a more careful investigation, in particular the structure of defects associated with N inclusion. The N doping of the a-Ge:H network appears to be very effective, the activation energy of the most effectively doped samples becoming around 120 meV. This is not the case with N-doped a-Si:H, the reasons for the difference remaining an open question. The lack of data on stoichiometric β-Ge3N4 prevents any reasonable assessment on the possible uses of the alloy in electronic and ceramic applications. © 1998 American Institute of Physics.841130Cotton, E.A., Wilkinson, G., Gaus, P.L., (1987) Basic Inorganic Chemistry, 2nd Ed., , J. Wiley, New YorkHarrison, W.A., (1980) Electronic Structure and the Properties of Solids, , W. 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