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[en] The annealing behaviour of ZnO has been studied using x-ray diffraction (XRD) and atomic force microscopy (AFM). Hydrothermally grown ZnO substrates were annealed in the range of (500-1050 deg. C), both in vacuum and different atmospheres/pressures, e.g., ambient air, pure oxygen, or in the presence of ZnO powder. Annealing at 0.5 bar oxygen results in degradation of both surface roughness and bulk crystallinity as measured by AFM and XRD. Increasing the oxygen pressure up to 1 bar improves the diffraction peaks but the surface remains rough. The best annealing results when considering stabilization/improvement of bulk and surface properties of ZnO are obtained for annealing in air at 680-960 deg. C, and for annealing in the presence of ZnO powder at 960 deg. C. The last result is discussed in terms of the establishment of a gas/solid equilibrium during annealing at the cost of the ZnO powder with its much higher surface to volume ratio compared to that of the wafer. In addition, these samples exhibit very flat, step-like terraces on the Zn-face terminated surface (root mean square roughness on terraces is in the range of 0.15 nm)
[en] We have studied the dynamics of the plasma glow of pulsed discharges (sliding surface discharge and combined volume discharge with plasma electrodes) in the nanosecond range (100–12 000 ns) in stationary air and in the flow behind the front of a plane shock wave with Mach numbers 1.7–5.0 in the shock tube channel. The temporal characteristics of the flow, the radiation spectra, and the discharge currents in air are compared in the pressure range 5–150 Torr, a pulsed voltage of 20–30 kV, and a current of about 1 kA. It is shown that the time of current under various conditions does not exceed 400 ns, and the duration of the glow can reach a few microseconds. It is shown that as a result of energy supply near the planar shock wave front, the decay of discontinuities occurs with the formation of shock waves and contact surfaces. The positions of the plasma glow regions are compared with the positions of discontinuity surfaces of numerically calculated gasdynamic parameters in the flow.
[en] Zinc oxide (ZnO) is a wide band gap semiconductor material with attractive features for light emitting devices, photovoltaics, chemical sensors and spintronics. In the past 10 yr ZnO has attracted tremendous interest from the materials science and semiconductor physics research communities, and in this review recent progress in (i) bulk growth, (ii) understanding of the role of hydrogen and (iii) formation of high-quality Schottky barrier (SB) diodes, are discussed for single crystalline ZnO. In (i), the emphasis is put on hydrothermally grown material and how the concentration of intentional and unintentional impurities, such as In and Li, can be controlled and modified by high temperature treatment and defect engineering involving vacancy clusters. In (ii), different possible configurations of hydrogen as a shallow donor are evaluated based on results from calculations employing the density-functional-theory as well as from experimental studies of local vibrational modes using Fourier transform infrared spectroscopy. Further, hydrogen is demonstrated to be very reactive and the interaction with zinc vacancies, group I and group V elements, and transition metals are elucidated. Moreover, the diffusion of hydrogen is found to be rapid and limited by the concentration of traps in hydrothermal samples, and it is argued that isolated (free) hydrogen is not very likely to exist in ZnO at room temperature. In (iii), a compilation of the literature data illustrates that the SB heights for metals deposited on n-type samples have no correlation with the metal work function, violating the fundamental Schottky-Mott model. The role of surface preparation cannot be overestimated and in several cases an oxidation of the surface prior to metal deposition is shown to be beneficial for the formation of high barrier SB diodes. The effects of near-surface defects, such as oxygen vacancies, and contact inhomogeneity are also addressed. However, in spite of the significant progress made in the past 5-7 years, a thorough understanding of the SB formation to ZnO is still lacking. Finally, results from characterization of electrically active point defects employing the SB contacts and junction spectroscopic techniques are reviewed and the identification of some prominent bandgap states is critically evaluated. (topical review)
[en] The modern radiation technology, nuclear engineering, non-linear optics are associated with radiation-resistant optical material study. Evolution of electronic excitations in these materials is a complex multichannel process which currently has no integrated model. A special role belongs to the low-symmetry single crystals, such as beryllium oxide (BeO). We present theoretical results that advance our understanding of exciton-based channel of electronic excitations relaxation. The four possible self-trapped exciton (STE) configurations in beryllia single crystal have been investigated by using a quantum mechanical approach (Hartree-Fock and B3LYP HF-DFT hybrid functional, as implemented in the CRYSTAL09 code). B3LYP DFT functional with 30% of exact exchange was used (B3LYP30). All calculations were performed using periodic boundary conditions and full SC geometry relaxation. The lattice distortion and charge density distribution for considered defect configurations were obtained. STE-A1 luminescence energy was found to be 6.0 eV for HF and 6.5 eV for B3LYP30; STE-A2 luminescence energy was found to be 9.2 eV for HF and 7.8 eV for B3LYP30. STE-B1 luminescence energy was found to be 5.5 eV for HF, 6.2 eV for B3LYP30; STE-B2 luminescence energy was found to be 4.7 eV for HF. (paper)
[en] Research building B at the Bochvar High-Technology Research Institute for Inorganic Materials (VNIINM) located within the city limits of a dense residential development was decommissioned in 2013–2015. Radioactively contaminated equipment and utility services were disassembled and removed, building structures were decontaminated, the framework was dismantled, the grounds of the development site were restored, and radioactive waste was transferred to specialized organizations. The framework was liquidated in strict accord with the norms and regulations governing the use of atomic energy.
[en] Deep level transient spectroscopy and minority-carrier transient spectroscopy (MCTS) have been applied to study electron-irradiated and proton-irradiated p-type Si samples with boron concentrations in the range of 6x1013-2x1015 cm-3. Both impurity-lean epitaxially grown samples and Czochralski grown samples have been investigated where some of the epitaxial samples were subjected to oxygenation prior to the irradiation in order to controllably vary the oxygen concentration. The MCTS measurements reveal a dominant electron trap at Ec-0.25 eV, where Ec is the conduction-band edge, commonly ascribed to a boron-interstitial oxygen-interstitial complex (BiOi). The amplitude of the level increases linearly with the irradiation dose and it anneals out at ∼175 deg. C but shows, however, no correlation with the boron concentration. The level is dominant even at doping concentrations in the 1013 cm-3 range and, irrespective of the oxygen concentration, the generation rate decreases by almost 50% as the boron concentration increases by a factor of ∼30. Comparison with numerical modeling reveals that these results are not consistent with the commonly accepted model of defect reactions in irradiated p-type Si. Different reasons for this discrepancy are discussed, such as an incomplete defect reaction model and alternative identifications of the Ec-0.25 eV level
[en] Processes of defect formation in radiation hard semiconductors exhibiting efficient dynamic annealing are different from those in amorphizible ones, and the latter are generally more well-studied. In the present work, we investigate structural disorder in wurtzite ZnO, which is a radiation hard material, implanted with different ions at room temperature and 15 K. The sample analysis was undertaken by Rutherford backscattering/channeling spectrometry performed in-situ without changing the sample temperature. The fluence dependence of bulk disorder exhibits the so-called IV-stage evolution, where the high fluence regime is characterized by both a strong influence on the damage build-up by the ion type and a reverse temperature effect. A straightforward methodology is demonstrated to differentiate between the contributions of pure ballistic and ion-defect reaction processes in the damage formation
[en] We have studied the effect of the Cd content on the recovery of ion-induced damage in wurtzite CdxZn1-xO (x ⩽ 0.05) films and compared with that in pure wurtzite ZnO and rock-salt CdO. 200 keV Au+ and 55 keV Ar+ ion implants were performed at room temperature in the dose range of 5 × 1014-6.5 × 1015 cm-2. Rutherford backscattering/channelling spectrometry was used to characterize the damage evolution in the course of annealing (600-900 °C in air). A complex defect annealing behaviour is revealed in CdZnO as a function of annealing temperature, Cd content and ion dose. In particular, defects in the low dose implanted CdZnO films can be effectively removed at 800 °C, while the high dose implantation results in the formation of defects stable at least up to 900 °C. Moreover, annealing of the CdZnO films is accompanied by Cd loss at the surface for temperatures exceeding 800 °C. In contrast, CdO exhibits a typical damage accumulation behaviour for metals and semiconductors with high degree of ionicity, resulting in saturation and extended defect formation at high ion doses. These extended defects in pure ZnO and CdO, formed either directly during implantation or by reconstruction during post-implant annealing, are substantially more stable compared with small defects which can be efficiently removed at 700 °C and 600 °C for ZnO and CdO, respectively. (paper)
[en] We report on the structural, chemical and optoelectronic properties of Fe-doped ZnO films deposited by dc magnetron sputtering. The effects of sputtering and post-growth thermal annealing conditions on structural and optical properties of ZnO films with different Fe contents were investigated by x-ray diffraction, XPS and photoluminescence techniques. The results are discussed taking into consideration the chemical state of the incorporated iron and altered balance of the intrinsic defect concentration.
[en] Positron annihilation spectroscopy was applied to study relaxed P-doped n-type and undoped Si1-xGex layers with x up to 0.30. The as-grown SiGe layers were found to be defect free and annihilation parameters in a random SiGe alloy could be represented as superpositions of annihilations in bulk Si and Ge. A 2 MeV proton irradiation with a 1.6x1015 cm-2 fluence was used to produce saturated positron trapping in monovacancy related defects in the n-type layers. The defects were identified as V-P pairs, the E center. The distribution of Si and Ge atoms surrounding the E center was the same as in the host lattice. The process leading to the formation of V-P pairs therefore does not seem to have a significant preference for either Si or Ge atoms. In undoped Si1-xGex we find that a similar irradiation produces a low concentration of divacancies or larger vacancy defects and found no evidence of monovacancies surrounded by several Ge atoms