Electron paramagnetic resonance of scandium in silicon carbide

The EPR spectra of scandium acceptors and Sc²⁺(3d) ions are observed in 6H-SiC crystals containing a scandium impurity. The EPR spectra of scandium acceptors are characterized by comparatively small hyperfine interaction constants, whose values are consistent with the constants for other group III elements in SiC: boron, aluminum, and gallium acceptors. The EPR spectra of scandium acceptors undergo major changes in the temperature interval 20–30 K. In the low-temperature phase the EPR spectra are characterized by orthorhombic symmetry, whereas the high-temperature phase has higher axial symmetry. The EPR spectra observed at temperatures above 35 K and ascribed by the authors to Sc²⁺(3d) ions, or to the A ²⁻ state of scandium, have significantly larger hyperfine structure constants and narrower lines in comparison with the EPR spectra of scandium acceptors. The parameters of these EPR spectra are close to those of Sc²⁺(3d) in ionic crystals and ZnS, whereas the parameters of the EPR spectra of scandium acceptors correspond more closely to the parameters of holes localized at group III atoms, in particular, at scandium atoms in GeO₂. It is concluded that in all centers the scandium atoms occupy silicon sites. Fiz. Tverd. Tela (St. Petersburg) 39, 52–57 (January 1997)     

Mass spectrometric investigation of low-temperature diffusion and solubility of helium in lead fluoride crystals

Thermal desorption of helium from presaturated crystals was used for mass spectrometric investigations of the diffusion and solubility of helium in lead fluoride crystals in the temperature range 606–714K which precedes the transition of the crystal to the superionic state. The experimental apparatus and measurement method are described and mechanisms for the diffusion and solubility of helium in PbF₂ are discussed. Zh. Tekh. Fiz. 68, 85–89 (December 1998)     

Structure and phase composition of a chromium-silicon system modified by high-current electron beams

The results of studies of the structure-phase state of a chromium-coated silicon substrate system’s subsurface layer treated with low-energy high-current electron beams, 50–200 μs in duration and with an energy density of 15 J/cm², are reported. The data of raster electron microscopy and X-ray structural and spectral microanalysis revealed the formation of a chromium-doped silicon layer with a thickness of 2–38 μm, chromium-enriched silicon dendrites, chromium disilicide CrSi₂, and an amorphous eutectic layer (the characteristic cross-section size of the chromium-enriched phase extrusions is ∼50 nm). The structure-phase transformations are discussed taking into account the peculiarities of the distribution of temperature, diffusion and convective mass-transfer in the modified layer.     

Spectroscopic properties of Pr<Superscript>3 + </Superscript>-doped erbium oxalate crystals

Spectroscopic properties of praseodymium ions-doped erbium oxalate (Er₂(C₂O₄)₃ · nH₂O) crystals have been investigated. The crystals were grown by hydro silica gel method under suitable pH conditions and by single diffusion method. The well-grown crystals are bright and transparent. The dark green colour of these crystals changes with the variation of the concentrations of the dopant ions. The absorption spectra have been measured in the region 200–800 nm at room temperature. Judd–Ofelt intensity parameters for f–f transitions of the Pr³⁺ ions have been determined as Ω₂ = 166.7, Ω₄ = 1.103 and Ω₆ = 2.898. Analyses of the absorption spectra also show a possible energy transfer from the host material to the dopant.     

Modeling of Cu gettering in p- and n-type silicon and in poly-silicon

Based on experimental findings we set up calculations of numerical modeling of gettering efficiencies for Cu in various silicon wafers. Gettering efficiencies for Cu were measured by applying a reproducible spin-on contamination in the 10¹² atoms/cm² range, followed by a thermal treatment to redistribute the metallic impurity. Subsequently, the wafers were analyzed by a novel wet chemical layer-by-layer etching technique in combination with inductively coupled plasma mass spectrometry. We investigated p/p+ and n/n+ epitaxial wafers with different doping levels and different substrate-doping species. We have also investigated gettering efficiencies of phosphorus-diffused p- and n-type wafers. Heavilyboron doped silicon exhibited a gettering efficiency of ∼100%, while gettering by n+ silicon occurred for doping levels >3×10¹⁹ atoms/cm³ only. In another set of experiments we investigated the dependence of the gettering efficiency of p-type wafers with poly-silicon back sides for different cooling rates and Cu spiking levels. A strong dependence on both parameters was found. Cu gettering in p/p+ epitaxial wafers was modeled by calculating the increased solubility of Cu in p+ silicon compared to non-doped silicon taking into account the Fermi-level effect, which stabilizes donors in p+ silicon, and the pairing reaction between Cu and B. Calculated gettering efficiencies were in very good agreement with experimental results. Gettering in n+ silicon was similarly modeled in terms of pairing reactions and the Fermi-level effect. But, for n-type silicon, many experimental uncertainties existed; thus, we applied our expressions to solubility data of Hall and Racette to obtain the unknown parameters. The empirical calculations were in good agreement even with results on n/n+ wafers. For phosphorus-diffused wafers we had to consider an excess vacancy concentration of 1.2–5.5 times the equilibrium concentration to explain the experimental findings by the model. Gettering by poly-silicon back sides was simulated by solving the time-dependent diffusion equation with boundary conditions that take into account different surface reaction rates of silicon point defects. Using this advanced model, the experimentally measured gettering efficiencies were reproduced within the uncertainty of the measurement. Received: 3 September 2001 / Accepted: 4 September 2001 / Published online: 20 December 2001     

Praseodymium-doped Ti:LiNbO3 waveguides

3 by diffusion doping is investigated by means of secondary neutral mass spectrometry and secondary ion mass spectrometry. The diffusion of praseodymium in LiNbO₃ can be described by Fick’s laws of diffusion with a concentration-independent diffusion coefficient and a limited solubility of praseodymium in LiNbO₃ increasing exponentially with rising temperature. The diffusion depends on the Li₂O content of the LiNbO₃ crystal. For LiNbO₃ crystals with a nominal slight difference in the congruent composition, the diffusion constants and activation energies for Z-cut LiNbO₃ are 3.28×10^-5 cm²/s and 2.27 eV, and 1.39×10^-5 cm²/s and 2.24 eV, respectively. Titanium-doped waveguides are formed in Pr:LiNbO₃ and characterised in relation to waveguide loss and absorption in the visible and near infrared. Received: 17 September 1998 / Accepted: 11 November 1998     

Electrochemical behavior of silicon compound in LiF–NaF–KF–Na<Subscript>2</Subscript>SiF<Subscript>6</Subscript> molten salt

The electrochemical reduction and nucleation process of Si⁴⁺ on an electrical steel electrode in the eutectic LiF–NaF–KF molten salt were investigated at 750 °C, by means of cyclic voltammetry and chronoamperometry technique. Silicon was electrodeposited on steel, and Fe₃Si was formed by the diffusivity of silicon on the electrode surface. The electrochemical reduction of Si⁴⁺ process in single-step charge transfer and the cathode process was reversible. The electrocrystallization process of silicon is controlled by progressive three-dimensional mechanism. The diffusion coefficient was calculated to be 5.42 × 10⁻⁷ cm²/s by chronopotentiometry at experimental conditions.     

Sulphur-doped silicon background-limited infrared photodetectors near 77 K

The photoconductive properties of sulphur-doped extrinsic silicon infrared detectors prepared by closed-tube diffusion techniques have been investigated. Spectral response data show that this material would be suitable for thermal imaging of 3–5 μm radiation, whilst detectivity measurements as a function of temperature indicate that background-limited operation is achievable near liquid nitrogen temperature (77 K).     

Temperature and orientation dependences of the grain-boundary diffusion coefficient of antimony in copper bicrystals

An investigation is made of the diffusion of antimony through the bulk and along grain boundaries in copper bicrystals containing a symmetric 〈100〉 misorientation boundary with misorientation angles from 20 to 37.2°. The bicrystals are grown by the method of horizontal zone recrystallization. The temperature range for these studies is 480–580 °C, where the solubility of Sb in Cu is about 6 atomic % and practically temperature-independent. The concentration profiles are obtained by x-ray spectral microanalysis, and the grain-boundary diffusion parameters are computed by the method of Whipple and Suzuoka. The orientation dependence of the triple product P=sδD _b (where s is the segregation coefficient, δ the width of the grain boundary, and D _b the grain-boundary diffusion coefficient) is nonmonotonic, with a maximum for the special ∑5 misorientation boundary (36.9°). The effective activation energy for grain-boundary diffusion ranges from ∼70 kJ/mol for ∑5 to140 kJ/mol for general boundaries. Fiz. Tverd. Tela (St. Petersburg) 39, 1153–1157 (July 1997)     

Mössbauer Study of Lanthanum–Strontium Ferromanganite Oxides

TDPAC has been employed to study the local structure of implanted palladium in silicon utilizing 87–75 keV γ–γ cascade of probe nucleus ¹⁰⁰Pd. The observed hyperfine parameters revealed the presence of Pd–V defect pair only in highly doped n-type silicon. A dumbbell structure with substitutional palladium and silicon vacancy as nearest neigbor is suggested for this defect.     

Pulsed electron-beam melting of a copper — steel 316 system: Evolution of the chemical composition,microstructure, and properties

The surface topography, chemical composition, microstructure, nanohardness, and tribological characteristics of a Cu (film, 512 nm)-stainless steel 316 (substrate) system subjected to pulsed melting by a low-energy (20–30 keV), high-current electron beam (2–3 μs, 2–10 J/cm²) were investigated. The film was deposited by sputtering a Cu target in the plasma of a microwave discharge in argon. To prevent local exfoliation of the film due to cratering, the substrate was multiply pre-irradiated with 8–10 J/cm². On single irradiation, the bulk of the film survived, and a diffusion layer containing the film and substrate components was formed at the interface. The thickness of this layer was 120–170 nm irrespective of the energy density. The diffusion layer consisted of subgrains of γ-Fe solid solution and nanosized particles of copper. In the surface layer of thickness 0.5–1 μm, which included the copper film quenched from melt and the diffusion layer, the nanohardness and the wear resistance nonmonotonicly varied with energy density, reaching, respectively, a maximum and a minimum in the range 4.3–6.3 J/cm². As the number of pulsed melting cycles was increased to five in the same energy density range, there occurred mixing of the film-substrate system and a surface layer of thickness ∼2 μm was formed which contained ∼20 at. % copper. Displacement of the excess copper during crystallization resulted in the formation of two-phase nanocrystal interlayers separating the γ-phase grains. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 6–13, December, 2005.     

Diffusion and solubility of helium in lead fluoride single crystals in the superionic transition region

Temperature curves of the diffusion coefficients and solubilities of helium in pure and holmium-doped lead fluoride crystals are obtained in the superionic phase-transition range. Possible mechanisms of the interaction of helium with ions are discussed, along with mechanisms of the solubility and diffusion of helium in a crystal. Fiz. Tverd. Tela (St. Petersburg) 40, 759–760 (April 1998)     

Radiation-induced conduction in quantum-confined p +-n silicon junctions

Electron-beam diagnostics are used to study the radiation-induced conduction of supershallow p ⁺-n silicon junctions obtained by nonequilibrium boron diffusion. Current-voltage (I–V) characteristics of radiation-induced conduction of a both forward-and reverse-biased p ⁺-n junction are demonstrated for the first time, which has been made possible by the presence of self-organized transverse quantum wells inside a supershallow p ⁺ diffusion profile. The variation of the dark-current I–V characteristics with electron irradiation dose shows that formation of self-organized longitudinal quantum wells inside supershallow p ⁺ diffusion profiles favors an increase of the breakdown voltage in p ⁺-n silicon junctions. Fiz. Tverd. Tela (St. Petersburg) 41, 1871–1874 (October 1999)     

Electronic excitations of Sc3+ impurity in α-Al2O3 crystals

Optical properties, including luminescence, of scandium-doped α-Al₂O₃ crystals have been studied in the VUV range. An absorption band associated with the scandium impurity was observed at the fundamental-absorption edge of crystalline corundum. A strong luminescence band peaking at 5.6 eV, which is most effectively excited within the 7.7–8.8-eV interval, was found. The kinetic and polarization characteristics of this luminescence were studied within the temperature range 6–500 K. An excitation model of the impurity complex and the mechanism of its relaxation are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 653–654 (April 1998)     

Transition and rare-earth elements in the SiC and GaN wide-gap semiconductors: Recent EPR studies

EPR studies of transition-element ions in SiC and GaN and of erbium in 6H-SiC are reported. Data are presented on Sc²⁺ ions and scandium acceptors, and chromium and molybdenum ions in various charge states in SiC. A study was made of nickel and manganese in nominally pure GaN grown by the sandwich sublimation method. The first EPR investigation of Er in 6H-SiC is reported. Erbium was identified from the hfs of the EPR spectra. Various possible models of erbium centers in silicon carbides are discussed. Strong room-temperature erbium-ion luminescence was observed. Fiz. Tverd. Tela (St. Petersburg) 41, 865–867 (May 1999)     

Phosphorus distribution profiles in 100-silicon using a spin-on source at low temperatures

 Incorporation of phosphorus into silicon from a spin-on dopant layer (SOD) at 400 ^°C is described. Annealing experiments were carried out with SOD films deposited on (100) silicon substrates by using the spin-on technique. Conventional heating on a hotplate in normal atmosphere and a temperature range up to 400 ^°C was used to study the dopant incorporation. After removing the SOD-films one part of the silicon substrates was annealed at higher temperatures. Investigations were carried out by SIMS, SAM, XPS, HTEM, stripping Hall and Van der Pauw measurements before and after the high temperature annealing. Chemical phosphorus concentration profiles obtained from low temperature annealed samples showed diffusion depths of 60–80 nm (extrapolated to a substrate doping level of 10¹⁶ cm^-3) and surface concentrations of 10¹⁹–10²⁰ cm^-3. Electron concentration profiles exhibiting maximum values around 2⋅10¹⁹ cm^-3 could be measured on high temperature annealed samples only. Received: 28 March 1996/Accepted: 19 August 1996     

Behavior of silicon implanted in gallium arsenide during a radiative anneal

We have studied the activation of silicon implanted in GaAs during a rapid thermal anneal with a protective layer and without it. It is found that during the anneal there is a diffusion redistribution of the silicon. The use of a dielectric coating during the anneal leads to a reduction both in the diffusion coefficient and also in the amount of electrical activation of the impurity. Tomsk Polytechnical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 44–48, November, 1998.     

Diffusion and solubility of electrically active iron atoms in gallium arsenide

Iron diffusion in GaAs at arsenic pressure 1 atm is studied. The temperature dependences of the diffusion coefficient and solubility of electrically active iron atoms in GaAs are determined. The dependences can be described by the Arrhenius equations with the following parameters: D ₀ = 1.61 cm²/s and E = (2.16 ± 0.47) eV (for diffusion) and N _S ⁰ = 4.62 ⋅ 10²³ cm⁻³ and E _S = (1.61 ± 0.16) eV (for solubility). The results obtained are compared with the earlier published data. The concentration of electrically active iron atoms is shown to be about 2 times lower than the total iron concentration in GaAs. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 39–41, November, 2008.     

Physical model for the evolution of the defect system of silicon carbide with allowance for the internal elastic stress fields during implantation of Al+ and N+ and subsequent annealing

A theoretical analysis is offered for the formation and development of defects in silicon carbide implanted with nitrogen and aluminum ions and then annealed. The diffusion of defects, the formation of complexes, and the influence of the internal elastic stress fields produced by the implanted ions and the created complexes on the migration of interstials are taken into account. The computed distributions of defects agree satisfactorily with the experimental data. Certain kinetic parameters of silicon carbide are estimated numerically. Zh. Tekh. Fiz. 69, 43–50 (October 1999)     

Formation and evolution of self-organized hexagonal patterns on silicon surface by laser irradiation in water

It was found that laser irradiation of silicon immersed in water can lead to regular hexagonal patterns on the silicon surface with period of ∼10 μm within several tens of minutes. The formation and the evolution of the surface patterns can be interpreted as Rayleigh–Taylor instability of the melted silicon layer under the interfacial pressure formed by fast boiling of the interfacial water at the laser-heated silicon surface. Based on the mechanism, a liquid film equation was proposed. The time evolution of the patterns was then compared with that of the well-defined classical Rayleigh–Taylor instability system. It showed that the two systems were qualitatively consistent in several aspects, supporting the Rayleigh–Taylor instability mechanism proposed.