V.S. Kortov

Self-consistent electrical charging of insulating layers and metal-insulator-semiconductor structures

By means of a computer simulation the self-consistent charge transport with the current densities j(x,t), the respective charges ρ(x,t), field strengths F(x,t), and potential distributions V(x,t) in SiO2 layers are obtained as a function of the insulator depth x and the injection time t. The SiO2 layers are considered as open layers on silicon substrate or they are embedded in metal-oxide-semiconductor (MOS) structures. The given currents of primary electrons, the field-dependent ballistic currents of secondary electrons and holes as well as the Fowler–Nordheim injection of electrons from the substrate into the dielectric layer are taken into account. This method allows a defined charge storage and the explanation of complicated emission, charging-up, and breakdown processes within insulating layers during electron bombardment and/or high-field charge injection from adjacent electrodes, e.g., in MOS structures.

Low-temperature photoluminescence of ion-implanted SiO 2 :Sn + films and glasses

Low-temperature photoluminescence spectroscopy with pulsed synchrotron excitation is applied to study the regularities of excitation and relaxation of both point defects and nanoparticles formed by tin implantation into SiO2 films and glasses. It has been found that tin implantation followed by air and nitrogen annealing yields the formation of α-Sn nanoclusters and nonstoichiometric SnOx nanoparticles, while a stable phase of SnO2 does not appear. Alternative channels of luminescence excitation are revealed for nanoclusters, including energy transfer from excitons and electron-hole pairs of the host SiO2 matrix.

Effect of structural changes on luminescent and dosimetric properties of nanoscale aluminum oxide.

Variations of the particle size and porosity of the alumina ceramics synthesized by annealing compacted nanopowder at 1500-1700°С in vacuum for various periods of time have been studied by SEM. Particle size distributions, which depend on the conditions of the ceramics synthesis, were obtained and discussed. The formation of fine grains and the growth of their fraction with the increasing annealing temperature increase the thermoluminescence intensity and expands the usable dose range upwards.

Computer simulation of the photoluminescence of nanostructured aluminum oxide excited with pulsed synchrotron radiation

An algorithm and a program are developed to calculate the photoluminescence (PL) parameters for bulk single-crystal and nanoscale dielectrics excited with pulsed synchrotron radiation. The luminescence spectra of F and F+ centers and the PL decay kinetics in single-crystal and nanoscale aluminum-oxide samples containing oxygen anion vacancies are calculated for various nanoparticle sizes. It is shown that a noticeable broadening of the bands and a decrease in the afterglow time is observed for nanoparticle sizes that are less than 20 nm.

Photoluminescence of nanostructured Zn 2 SiO 4 :Mn 2+ ceramics under UV and VUV excitation

The photoluminescence of Zn2SiO4:Mn2+ ceramics with a particle size of 120 ± 10 nm, which is excited in the range of 3.5–5.8 eV and subjected to synchrotron radiation with photon energies of up to 20 eV, is investigated. Nanoscale Zn2SiO4:Mn2+ ceramics possesses intense luminescence with a maximum of 2.34 eV, the position and half-width of the band are independent of the excitation energy. It is found that the photoluminescence at 2.34 eV decays nonexponentially upon ultraviolet excitation. In the case of nanoscale ceramics is irradiated by vacuum ultraviolet, an additional photoluminescence-excitation channel is likely to occur due to interaction of band states and intrinsic vacancy-like defects of the Zn2SiO4 matrix.

Photoluminescence of implantation-induced defects in SiO2:Pb+ glasses

The luminescence of quartz glass with implanted Pb+ ions is investigated by time-resolved photoluminescence spectroscopy under synchrotron excitation. It is established that the glass layer modified with ions represents a microheterogeneous medium with a variable content of implanted ions predominantly in the form of Pb2+. Three different types of emission centers are detected that are created by radiation-induced defects of the SiO2 matrix and localized electronic states of the amorphous lead-silicate phase.

Phototransferred Thermoluminescence of Dosimetric α-Al2O3 Crystals Irradiated by a Pulsed Electron Beam

The thermoluminescence (TL) of deep traps of anion-defective alumina monocrystals irradiated by a high-dose (more than 1 kGy) pulsed electron beam (130 keV) is studied. The deep traps in the studied material are classified according to the TL temperature range. It is demonstrated that the phototransferred thermoluminescence (PTTL) in the temperature range of the main TL peak is induced by optical charge migration from deep traps that are emptied at 400–470 and 470–600°C. An anomalous PTTL enhancement in crystals subjected to stepped annealing in the 350–400°C interval is observed. It is demonstrated that this effect may be caused by competing processes of charge transfer that involve deep traps corresponding to the TL peak at 390°C. The applicability of PTTL in the dosimetry of high-dose (1–50 kGy) pulsed electron beams is established.

The contribution of hole traps to thermoluminescence of the dosimetric peak in anion-defect α-Al 2 O 3 single crystals

The thermoluminescent properties of anion-defect alumina single crystals with different FWHMs of the main (dosimetric) peak at 400–500 K are studied. New experimental evidence in favor of the hole nature of traps associated with the high-temperature part of this peak are presented. The introduction of hole trap centers into analysis provided theoretical justification for the experimentally observed dependences of the thermoluminescence (TL) intensity, the temperature position of the main peak, and its FWHM on the occupancy of deep traps. The hole nature of traps of the high-temperature part of the main TL peak is confirmed by the results of examination of specific TL features of shallow trap centers, which govern TL at 350 K, and the temperature variation of the main TL peak spectrum.

Photoluminescence of the nanosized xerogel Zn2SiO4:Mn2+ in pores of anodic alumina

The photoluminescence properties of a composite material prepared by the introduction of the nanosized phosphor Zn2SiO4:Mn2+ into porous anodic alumina have been investigated. Scanning electron microscopy studies have revealed that Zn2SiO4:Mn2+ particles are uniformly distributed in 70% of the volume of the pore channels. The samples exhibit an intense luminescence in the range of 2.3–3.0 eV, which corresponds to the emission of different types of F centers in alumina. After the formation of Zn2SiO4:Mn2+ nanoparticles in the pores, an intense photoluminescence band is observed at 2.4 eV due to the 4T1–6A1 electronic transition within the 3d shell of the Mn2+ activator ion. It has been found that the maximum of the photoluminescence of Zn2SiO4:Mn2+ xerogel nanoparticles located in the porous matrix is shifted to higher energies, and the luminescence decay time decreases significantly.

Photo- and cathodoluminescence of strontium titanate xerogel films doped with terbium ions

Terbium-doped strontium titanate thin films are synthesized via the sol–gel method. The xerogel is deposited onto single-crystal silicon and porous anodic alumina substrates formed on single-crystal silicon. The structure and phase composition of the films are studied. The strontium titanate xerogel on single-crystal silicon exhibits a photoluminescence spectrum with a selective terbium emission band that is difficult to identify. The photoand cathodoluminescence spectra of the xerogel in porous matrices contain emission bands due to the electronic transitions of trivalent terbium.