[en] We studied the process of stabilization of the F sup(+) sub(2) centers in irradiated LiF:OH sup(-) single crystals. A consistent investigation of the wide number of defects produced by the radiation damage in the lattice allowed us to improve the experimental conditions to increase the final number of stabilized F sup(+) sub(2). It has been established the model for the F sup(+) sub(2):O sup(2-) formation in LiF:OH sup(-) irradiated based on a statistical distribution of the defects produced during the electron irradiation at 230K. These stabilized centers are formed during the thermal diffusion of the anionic vacancies in competition with the isolated F sup(+) sub(2) centers. A critical distance of thirteen lattice parameters determined for a vacancy suggested that the O sup(2-) -α dipole is the precursor entity for the F sup(+) sub(2):O sup(2-) creation. A further increasing of the F sup(+) sub(2) stabilized concentration was obtained after the e sup(-) - irradiation and the vacancy generation process by irradiating the samples at 77K with a small dose of gamma rays. The same net effect was seen after the e sup(-) - irradiation by keeping the samples at room temperature for at least 6 months as a consequence of the thermal activated diffusion of the remaining O sup(2-) -α dipoles and reaction with F centers. The sub-products of the OH sup(-) dissociation induced by the high energy irradiation were identified by spectroscopical analysis. A new defect was identified as a F sub(z) center containing a water molecule. Its luminescence properties and stability has been determined. Future investigations and some implications from the model has been discussed. (author)

[en] Although thermoluminescence (TL) has received much attention with respect to radiation dosimetry, the nature of the TL producing mechanisms is still quite obscure. The purpose of this paper is to extend the model of Nink and Kos and to show that the derived expressions can be used to calculate the relative concentrations of Z₂ and Z₃ centers with respect to the LET values of the TL producing radiation

No abstract available

[en] Recent progress and current understanding of carrier lifetimes and avalanche phenomena in silicon carbide (SiC) are reviewed. The acceptor level of carbon vacancy (V _C), called the Z _1/2 center, has been identified to be the primary carrier lifetime killer in SiC. The V _C defects can be eliminated by the introduction of excess carbon atoms followed by carbon diffusion in the bulk region. The true bulk lifetime after V _C elimination was estimated to be approximately 110 µs. The doping dependence of carrier lifetimes in n- and p-type SiC is also presented. The impact ionization coefficients of electrons and holes were extracted in the temperature range of 298 to 423 K. The intrinsic critical electric field strength of SiC〈0 0 0 1〉 was determined to be 2.0, 2.5, and 3.3 MV cm⁻¹ for doping densities of 1  ×  10¹⁵, 1  ×  10¹⁶, and 1  ×  10¹⁷ cm⁻³, respectively, at room temperature; it slightly increased at elevated temperature. The obtained set of impact ionization coefficients has enabled us to accurately predict the breakdown voltage of SiC devices, including its temperature dependence. Due to the unusually low impact ionization coefficient of electrons, the breakdown voltage of a SiC p⁺n junction is about 6%–9% higher than that of an n⁺p junction with a given doping density. (topical review)

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[en] A Z-centre model was proposed by Nink and Kos (Phys. Status Solidi a; 35:121 (1976) and Nucl. Instrum. Methods; 175:16 (1980)) to explain the thermoluminescent response of LiF. That model has been criticised by several authors. A modified version of the Z-centre model has since been proposed. This letter points out that even the modified version does not stand scrutiny. (author)

[en] Recent ab initio calculations [Mattausch et al., Phys. Rev. B 70, 235211 (2004)] of carbon clusters in SiC reveal a possible connection between the tricarbon antisite (C₃)_Si and the U photoluminescence center in 6H-SiC [Evans et al., Phys. Rev. B 66, 35204 (2002)]. Yet, some of the predicted vibrational modes were not observed experimentally. We report experiments that, indeed, confirm the existence of a low-energy mode for the U center (as well as for the HT3 and HT4 centers with spectral details similar to the U center). We calculated the isotope splitting for the (C₃)_Si-defect and found near-perfect agreement with our data. In addition, we discuss the carbon di-interstitial (C₂)_Hex as a model for the Z and HT5 centers. The isotope splitting is also well reproduced, but the absolute values of the local mode energies show a discrepancy of about 10 meV

[en] From the room temperature and low temperature optical bleaching behavior of γ-ray induced optical absoption bands in TLD-100 (LiF:Mg, Ti) the optical absorption bands at 4.0 and 5.5 eV are attributed to Z₂ and Z₃ centers, respectively, while the absorption band at 3.24 eV appears to be due to a Z₂ center which has captured an additional electron. A center, stable at low temperatures with an optical absorption at 3.5 eV, results from the trapping of electrons, released by bleaching at 90 K. (author)

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No abstract available