I. V. Antonova

Effect of annealing at argon pressure up to 1.2 GPa on hydrogen-plasma-etched and hydrogen-implanted single-crystalline silicon

Effect of annealing at up to 1400 K under argon pressure up to 1.2 GPa on hydrogen — plasma — etched and hydrogen — implanted Czochralski or FZ silicon was investigated by SIMS, X — ray, TEM, electrical, infrared and photoluminescence methods.

DLTS study of oxygen precipitates in silicon annealed at high pressure

Abstract The evolution of oxygen precipitates (OPs) created at 900–1000 K in SiCz with initial oxygen concentration 8 × 1017 cm−3 was studied by DLTS technique. The samples were subjected to high pressure (HP) treatment up to 1.3 GPa at high temperature (HT, 1230–1550 K) which caused a partial dissolution of OP. A new way of studying the oxygen distribution is suggested. It is based on the investigation of an electrically active complex of the oxygen atom with a vacancy (A-center, level Ec − 0.18 eV). A-centers were introduced by 3.0 MeV electron irradiation with dose 1 × 1015 cm−2 and DLTS was used for A-center agglomerates detection. The analysis of data obtained allows one to conclude that the irradiation dose used does not decompose OPs. It has been found that hydrostatic pressure retards OP dissolution at HT treatment through a decrease in the migration energy E a, coefficient Do and diffusion coefficient D. The effect is explained on the assumption that oxygen diffuses in the form of connected pairs of the oxygen and self-interstitials.

Nucleation and formation of oxygen precipitates in Czochralski grown silicon annealed under uniform stress conditions

Abstract Annealing of Cz-Si at enhanced pressures gives rise to the creation of oxygen precipitates with smaller sizes and higher concentrations in comparison to the case of annealing at atmospheric pressure. This effect is more pronounced for pressures above 0.1GPa. The pressure (about 1.0GPa) treatment at temperatures below 900°C leads to the stabilization of the OP precursors (of the local oxygen reach areas) and after prolonged annealing to their coexistence with OP. The last effect is most likely connected with a decrease in the OP size with pressure to some critical value which is lower than that needed for OP existence.

Functionalization of graphene and few-layer graphene films in an hydrofluoric acid aqueous solution

The possibility of the controlled modification of the properties of graphene and few-layer graphene significantly extends the scope of their potential applications. Conditions for the chemical modification of graphene and few-layer graphene in an hydrofluoric acid aqueous (HF) solution were revealed in this work. The following changes in the properties of films upon their treatment in an aqueous HF solution were observed: a sharp (by 5–7 orders of magnitude) jump in the resistance of samples, the suppression of characteristic peaks in Raman spectra, the occurrence of peaks from fluorine ions F (687.7 eV) and C-F bonds (288 eV) in X-ray photoelectron spectroscopy (XPS) spectra, and the formation of a nanorelief on the surface. The reaction with HF possesses an activation character (with an energy of 1.4 eV), depending on the temperature; the reaction proceeds in a narrow range of concentrations of HF solution and is reversible. An array of experimental data made it possible to suggest that the functionalization of films was due to fluorination. The recovery of the conductivity of films after the annealing of samples at a temperature of 450°C (the energy of activation of the annealing ∼2 eV) is one of the confirmations of the fluorination process. It was shown that the fluorination reaction in an aqueous HF solution was initiated on the grain boundaries of polycrystalline films of graphene and few-layer graphene. It was found that the interaction of few-layer graphene with HF depended significantly on the thickness of samples and their preliminary treatment. A model for the fluorination of a few-layer film based on the corrugating of layers because of the difference in the lattice constants of graphene and fluorographene was suggested.

Colloidal solutions of niobium trisulfide and niobium triselenide

Exfoliated nanomaterials, such as graphene and related few-layered materials, are now widely studied for electronic devices, electrodes and composites, so it is desirable to demonstrate exfoliation of a wider number of layered materials. We have shown that bulk niobium trichalcogenides NbS3 and NbSe3 may be stably dispersed in a number of common organic solvents by ultrasonic treatment. The most concentrated dispersions are obtained in alcoholic media (up to ∼0.443 g L−1). The colloids contain thin well-crystallized nanoribbons of NbS3 and NbSe3. Filtration or spraying of the colloids produces strongly textured thin films with good conducting properties.

Vertical heterostructures based on graphene and other 2D materials

Recent advances in the fabrication of vertical heterostructures based on graphene and other dielectric and semiconductor single-layer materials, including hexagonal boron nitride and transition-metal dichalcogenides, are reviewed. Significant progress in this field is discussed together with the great prospects for the development of vertical heterostructures for various applications, which are associated, first of all, with reconsideration of the physical principles of the design and operation of device structures based on graphene combined with other 2D materials.

Electrical properties and photoluminescence of SiOx layers with Si nanocrystals in relation to the SiOx composition

The photoluminescence and electrical properties are compared for silicon-oxide layers containing Si nanocrystals and having different Si content. The oxide was deposited by co-sputtering of silicon dioxide and silicon with the subsequent annealing for the formation of nanocrystals. Excess Si content in the layer varies along the sample from 6 to 74 vol %. It is found that a charge magnitude determined from the flat-band voltage has a pronounced peak for the excess Si content of about 26%, the largest charge correlating with the highest photoluminescence intensity. The further increase in the excess Si content in oxide leads to a decrease in both the oxide charge and the photoluminescence intensity and to the appearance of percolation conductivity.

Comparison of various methods for transferring graphene and few layer graphene grown by chemical vapor deposition to an insulating SiO2/Si substrate

The objective of this study is to compare the results of transferring graphene and few layer graphene (FKG) up to 5 nm thick, grown by chemical vapor deposition (CVD) at a reduced pressure to a SiO2/Si substrate using four different polymer films. The chosen transfer methods are based on the most promising (according to published data) materials: polymethyl methacrylate, polydimethylsiloxane, thermoscotch, and polycarbonate. It is shown that the most promising transfer method (minimum resistance and maximum carrier mobility) lies in the use of polycarbonate thin films with their dissolution in chloroform. In this case, the following parameters are steadily obtained: the graphene and FLG resistance is 250–900 Ω/□ and the carrier mobility is 900–2500 cm2/(V s).

Electrical properties of multiple-layer structures formed by implantation of nitrogen or oxygen and annealed under high pressure

Silicon-on-insulator-like structures formed in either oxygen- or nitrogen-implanted silicon during anneals under atmospheric and enhanced hydrostatic pressure are characterized by means of electrical techniques (current-voltage and capacitance-voltage measurements). It was found that the application of high pressure (∼1GPa) stimulates the formation of a perfect top silicon layer and results in the degradation of the properties of the buried insulator. The latter effect is caused by defect accumulation in the buried insulator and leads to a decrease in the effective thickness of the insulator layer as extracted from capacitance-voltage measurements. Pressure-stimulated formation of electrically active centers (donors and acceptors) in the top silicon layer and substrate was found. The fixed charge in the oxide was found to be independent on the pressure applied during anneals, whereas the negative charge in the nitride increased with pressure.

Electrical conductivity of silicon-on-insulator structures prepared by bonding silicon wafers to a substrate using hydrogen implantation

Silicon-on-insulator structures were prepared by exfoliating a thin layer from a silicon wafer owing to hydrogen implantation, transferring this layer to another substrate, and bonding to it. The influence of hydrogen and the doping level in the original wafers on the free-carrier concentration and the conductivity type in the split-off silicon layer was investigated. A high boron concentration in the original material, together with a high concentration of residual hydrogen in the silicon layer exfoliated from the wafer, was shown to result in n-type conduction, which is retained up to annealing temperatures of 1100°C in these structures. A decrease in the residual hydrogen concentration owing to additional annealing creates the conditions under which the conductivity of resulting structures corresponds to the conductivity type of the original material.