Results 1 - 10 of 533
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[en] The effect of UV (253.7 nm) bleaching and subsequent thermal annealing treatment in the range 400-500 deg. C, were studied in order to investigate the role of E1'-centre on sensitization of 110 deg. C and 220 deg. C peaks in quartz. The decay of E1'-centre in thermal annealed samples and observation of E1'-centres after UV bleach, accompanied by desensitization of TL in the quartz sample, appears to lend support to the role of competing traps and E1'-centres in the sensitization process
[en] In this paper, using first-principles calculations, we demonstrate that vacancies and E-centers (AsV, SbV) in silicon can co-exist in several metastable configurations with notably different relaxation patterns, which have very similar formation energies. Thus these vacancy-type defects can be considered as multi-symmetry defects in the sense that, at elevated temperatures, the probabilities to find vacancies in different stable configurations are comparable. From an experimental point of view, the co-existence of various symmetries can complicate the identification of the defect.
[en] Up to now, P diffusion in Ge is modeled with an effective diffusivity involving at most a quadratic dependence with the free electron concentration (n). However, recent theoretical studies suggest the existence of a triply negatively charged state for the free vacancy in germanium and experimental data indicate that the E center (PV pair) in Ge has a double acceptor state. These two facts would be consistent with a diffusivity model involving a cubic dependence with n. In this paper the validity of this approach is checked for both pure thermal diffusion (intrinsic and extrinsic) and implanted phosphorus, using either our own experiments or other data available from the literature. Although some discrepancies still exist in some cases for the redistribution of implanted P, it is shown that the introduction of this cubic dependence significantly improves the overall agreement as compared with the usual model.
[en] Room-temperature electron paramagnetic resonance (EPR) studies (at ca. 9.85 GHz) of γ- and x-irradiated alpha-quartz are reported and discussed. The previously described E'2 center has been proved to be associated with hydrogen, and this center's primary silicon-29 hyperfine coupling matrix has now been accurately determined, as were its hydrogen hyperfine coupling and electronic Zeeman splitting (g) matrices. The paramagnetic center is believed to arise from attack on a diamagnetic oxygen-anion vacancy V(O0) (E center) effectively by an electron and a proton arising from atomic hydrogen produced in the irradiation process. A second very similar center, called E'2(II) herein, was discovered and its parameter matrices too have been obtained by EPR, and it was modelled as described herein. It is proposed that the proton in E'2 resides on an oxygen anion adjacent to the vacancy species. Comparison is made of the spin-Hamiltonian parameter matrices and the choice of best symmetry-related sites expressing them, for the various centers E'-1E'4. (author)
[en] By the method of Moessbauer spectroscopy on the 67Cu(67Zn) isotope it is shown, that zinc impurity in the silicon is the two-electron acceptor. The sign of correlation energy for two-electron zinc centers is found
[en] We present theoretical evidence that the paramagnetic E† defect centers in amorphous silicon dioxide (a-SiO2 ) do not have the same microscopic structures as those well-defined in the corresponding crystalline counterparts such as α-quartz . We then present alternative models of some paramagnetic defects that account for the underlying experimental features of the E† -center variants in a-SiO2 . We suggest that our new model should take the place of the conventional defect model of a-SiO2
[en] A linear relation between the age of α-quartz and its E' centre concentration has been found when the product Qt is far smaller than 1, where Q is the uranium content in equilibrium (g/g) and t is the age (Ma). This relation can be used to determine the age of α-quartz by measuring the E' centre concentration after calibration with a reference sample
[en] The group- V vacancy pair, the so-called E-center, has recently been demonstrated to have, both in Si and Ge, more complicated energy-level schemes in the energy gap than were previously assumed. The E-center in silicon has, in addition to its well-established single-acceptor level in the upper half of the band gap, also a donor level in the lower half of the band gap; this donor level has lain hidden for more than 40 years. The E-center in Ge has an even more complicated level scheme as it induces, in addition to two levels analogous to those found in Si, also a double-acceptor level in the upper half of the band gap. Thus the E-center in Si can exist in three charge states and the E-center in Ge in four
[en] A review is presented on irradiation-induced vacancy-type defects in relaxed Si1-xGex. The emphasis is put on results extracted from deep-level transient spectroscopy (DLTS) investigations of the vacancy, the di-vacancy, the oxygen-vacancy pair (the A-center) and the group-V-vacancy pair (the E-center). The positions of the associated levels in the band gap will in particular be followed as a function of the Ge content and, consequently, of the monotonic decrease of the band gap
[en] Investigations of γ-luminescence spectra in quartz-polymer fibers and influence of reabsorption process on the measured spectra are presented. It is shown that the luminescence spectra are exposed to deformation due to reabsorption of luminescence caused by γ-induced color centers. The influence of reabsorption on luminescence spectra increases with growth of irradiation dose and length of irradiated part of optical fibers. The method for measurement and calculation of real luminescence spectra with exception of the contribution reabsorption process are offered.(author)