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On the kinetics of the generation of point defects in the Si-SiO2 system

The results of studies of the point-defect generation kinetics in the Si-SiO2 system by means of Electron Spin Resonance (ESR) and InfraRed (IR) absorption spectroscopy are presented. The influence of oxidation conditions (oxidation temperature and time, cooling rate) on the defect structure of the Si-SiO2 interface has been studied. It is shown that this influence can be explained by the model of point-defect generation proposed by Tan and Gösele, and the structural properties of the Si-SiO2 system can be improved by an appropriate choice of the oxidation conditions.

Trapped-hole centers in MgO single crystals

The properties of the majority trapped-hole centers in MgO, such as g-factors, positions of absorption and luminescence bands, and temperatures of thermal destruction, have been analyzed with the emphasis on the observed regular trends and interrelations between the properties of these centers. Particular emphasis has been placed on the positively charged [Be]+ and [Ca]+ trapped-hole centers, which have a large cross section for recombination with conduction electrons. In these centers, a hole is localized at an oxygen ion near the impurity Be2+ or Ca2+ ion located at a regular cation site. The generation and transformation of defects due to the recombination of either relaxed conduction electrons with OH−-containing hole centers or cold and hot electrons with [Be]+ and [Ca]+ centers have been considered. Using the interrelation of the characteristics of hole centers and taking into account that the recombination emission band revealed at ∼6.8 eV is due to the Ca2+-containing centers that are stable below 50 K, the prospects for the EPR detection of the [Ca]+ center at T < 4.2 K have been discussed.

Electron paramagnetic resonance of the [Be]+ centre in MgO:Be

In Be-doped MgO crystals, a new hole centre has been discovered whose physical properties are similar to those of [Li]0-type centres (a hole localized at a cation impurity). The centre can be observed best by electron paramagnetic resonance (EPR) at liquid He temperature; thermal destruction of the centre through the loss of a hole takes place at about 160 K. The symmetry of the centre is almost tetragonal, with a slight rhombic distortion, and the hyperfine structure of its EPR spectrum suggests the following model for the centre: Be2+–O−. However, a detailed investigation of the temperature dependence of the EPR spectrum did not reveal, contrary to our preliminary announcement, any temperature averaging. At higher temperatures the spectrum is complicated by the wealth of spectral lines induced by the ubiquitous Be impurity ions. In particular, this led to our former misinterpretation. The physical properties of the observed centre are discussed and compared with those of analogous centres in MgO.

Anion interstitials in neutron-irradiated MgO single crystals

Electron paramagnetic resonance (EPR) and high-temperature (300 –775 K) thermoluminescence of neutron-irradiated MgO single crystals were studied. Spin-hamiltonian parameters of the observed anion interstitial centres (O − molecular ion in an oxygen site by a cation vacancy—H centre) were determined. The thermal stability of anion interstitials (H centres) and other EPR-active centres was investigated. It is shown that the thermal decay of H centres is attended by a TL peak due to hole recombination luminescence at 700 K. A possible mechanism for the thermal destruction of anion Frenkel defects in MgO is discussed. c � 2001 Elsevier Science Ltd. All rights reserved.

High-temperature thermoluminescence manifestations of anion interstitials in neutron-irradiated pure and doped single crystals of MgO

Abstract The thermal stability of anion interstitials (H centers) was studied in neutron irradiated single crystals of MgO. The ESR spectra of H centers were investigated, the annealing of their ESR absorption and the optical absorption of F+ centers was measured. Both defects were found to disappear in the 650—750 K temperature region. Thermal decay of H centers was investigated using fractional thermoactivation spectroscopy and a common high-temperature (300—775 K) thermoluminescence, combined with the method of controlled X-colouration. A possible mechanism for the thermal destruction of complex anion Frenkel defects in MgO, including the hopping diffusion of neutral oxygen interstitials to F centres, is proposed.

VOH?Be?a new and unusual member in the family of V centres

In Be-doped MgO crystals a new V centre has been discovered whose physical properties differ significantly from those of other V centres. The centre can be observed by means of EPR at room temperature; the shift of its g-factor from the free electron value is about 1.6 times smaller than that of a VOH centre, the optical absorption band is shifted by ~1 eV to higher energies, and the thermal destruction of the centre through the loss of a hole takes place at about 400 K. The axial symmetry of the centre and the hyperfine structure of its EPR spectrum suggest the following model of the centre: Be2+?O??vc?OH?. The specific physical properties of the VOH?Be centre are explained by an interaction of the effective electric dipole, created by the off-centre position of the Be2+ ion substituting for the Mg2+, with the nearby localized hole.

Paramagnetic Centres in Be-Doped MgO Single Crystals

Using a variation of arc-fusion technique, Be-doped MgO single crystals were grown, in which about 0.01% of the cation sites are occupied by Be2☎. This gives rise to a variety of Be-containing paramagnetic centres, easily detectable by EPR. The models of the centres are proposed and the values of their spin-Hamiltonian parameters are determined and discussed. Two of them—VOH-Be and H-Be centres—stem from well-known paramagnetic centres such as VOH, and interstitial H atom. In addition, because of the non-central position of the ion, an isolated Be2☎ can trap a hole forming a Be2☎O− centre. The symmetry of the Be2☎O− centre at T<30K is rhombic, at a higher temperature a motional averaging of the spectrum takes place. It is shown that unusually for V centres physical properties of the VOH-Be centre (a relatively small g-factor anisotropy and high thermal stability, optical absorption energy and spin-lattice relaxation time) arc caused by the non-central position of the Be2☎ ion.

Effect of Ultrasonic Treatment on the Defect Structure of the Si-SiO2 System

The effect of ultrasonic treatment (UST) on the defect structure of the Si–SiO2 system is characterised by means of electron spin resonance (ESR), metallography, MOS capacitance measurements and secondary ion mass spectroscopy (SIMS). A non-monotonous dependence of the defect densities on the ultrasonic wave intensity has been observed. The influence of the UST frequency on the ESR signal intensity of the defect centres depended on the defect’s type and structure and may be caused by vibrational energy dissipation which is a function of the defect centre’s type. The influence of the UST on the Si–SiO2 interface properties depends on the oxide thickness and crystallographic orientation. The density of point defects and absorbed impurities at the Si–SiO2 interface can be reduced and its electrical parameters improved by an appropriate choice of UST and oxidation conditions.

Point Defects Generation Kinetics in the Si-SiO2 System and its Influence on the Interface Properties

It has been shown by means of EPR and NMR technique that at the Si-SiO2 interface at appropriate oxidation temperature (time) local dynamical equilibrium may be achieved. At oxidation temperature 1130oC the dencity of point defects is less than at lower and higher temperature (1100oC and 1200°C) and the content of absorbed impurities (hydrogen, oxygen) diminishes.