A. I. Belov

Formation and “white” photoluminescence of nanoclusters in SiOx films implanted with carbon ions

Experimental data on ion synthesis of nanocomposite layers with carbon-rich clusters and silicon nanocrystals by irradiation of nonstoichiometric silicon oxide (SiOx) films with carbon ions followed by high-temperature annealing are reported. It is shown that, at rather high doses of C+ ions, the resulting films exhibit photoluminescence with a spectrum that encompass the entire visible and near-infrared regions. The formation of carbon-rich clusters and silicon nanocrystals is confirmed by X-ray photoelectron spectroscopy data. The distribution of carbon practically reproduces the calculated profile of ion ranges, suggesting that there is no noticeable diffusive redistribution of carbon. A qualitative model of the layered structure of ion-synthesized structures is suggested.

Resistive switching in metal-insulator-metal structures based on germanium oxide and stabilized zirconia

Bipolar resistive switching in metal-insulator-metal structures based on a double-layer insulator composed of a layer of yttria-stabilized zirconia (YSZ) containing 12 mol % Y2O3 and a layer of GeOx is studied. It is shown that the incorporation of an additional GeOx layer into the structure leads to a significant decrease in the variation of resistive switching parameters at both negative and positive voltages. Au/Zr/GeOx/YSZ/TiN structures exhibit a high stability of the resistance ratio in high-resistance and low-resistance states during cyclic switching. The studied structures can be used for designing next-generation nonvolatile memory elements.

Chemical and phase compositions of silicon oxide films with nanocrystals prepared by carbon ion implantation

The chemical and phase compositions of silicon oxide films with self-assembled nanoclusters prepared by ion implantation of carbon into SiOx (x < 2) suboxide films with subsequent annealing in a nitrogen atmosphere have been investigated using X-ray photoelectron spectroscopy in combination with depth profiling by ion sputtering. It has been found that the relative concentration of oxygen in the maximum of the distribution of implanted carbon atoms is decreased, whereas the relative concentration of silicon remains almost identical over the depth in the layer containing the implanted carbon. The in-depth distributions of carbon and silicon in different chemical states have been determined. In the regions adjacent to the layer with a maximum carbon content, the annealing results in the formation of silicon oxide layers, which are close in composition to SiO2 and contain silicon nanocrystals, whereas the implanted layer, in addition to the SiO2 phase, contains silicon oxide species Si2+ and Si3+ with stoichiometric formulas SiO and Si2O3, respectively. The film contains carbon in the form of SiC and elemental carbon phases. The lower limit of the average size of silicon nanoclusters has been estimated as ∼2 nm. The photoluminescence spectra of the films have been interpreted using the obtained results.

Effect of coalescence and of the character of the initial oxide on the photoluminescence of ion-synthesized Si nanocrystals in SiO2

The photoluminescence intensity (PLI) related to Si nanocrystals in a SiO2: nc-Si system synthesized by ion implantation is studied experimentally and theoretically as a function of the Si+ ion dose at various annealing temperatures Tann (1000–1200°C). The dose corresponding to the maximum PLI is found to decrease with increasing Tann. These data are explained in terms of a model taking into account the coalescence of neighboring nanocrystals and the dependence of the probability of radiative recombination of quantum dots on their size. It is found that, when silicon oxide is grown in a wet atmosphere, the photoluminescence spectrum contains an additional band (near 850 nm), which is related to shells around the nanocrystals. This band weakens abrupily after high-temperature annealing in an oxidizing atmosphere (air).

Layer-by-layer composition and structure of silicon subjected to combined gallium and nitrogen ion implantation for the ion synthesis of gallium nitride

The composition and structure of silicon surface layers subjected to combined gallium and nitrogen ion implantation with subsequent annealing have been studied by the X-ray photoelectron spectroscopy, Rutherford backscattering, electron spin resonance, Raman spectroscopy, and transmission electron microscopy techniques. A slight redistribution of the implanted atoms before annealing and their substantial migration towards the surface during annealing depending on the sequence of implantations are observed. It is found that about 2% of atoms of the implanted layer are replaced with gallium bonded to nitrogen; however, it is impossible to detect the gallium-nitride phase. At the same time, gallium-enriched inclusions containing ∼25 at % of gallium are detected as candidates for the further synthesis of gallium-nitride inclusions.

Photoluminescence of porous silicon saturated with tungsten-tellurite glass with rare-earth metal impurities

It has been shown that the presence of silicon nanoparticles in a layer of porous silicon saturated with tungsten-tellurite glass causes an increase in the photoluminescence quantum efficiency of erbium (1530 nm) by an order of magnitude in the case of long-wavelength excitation and an enhancement of the ytterbium photoluminescence (980 nm) by almost 50 times and erbium photoluminescence by 25 times in the case of short-wavelength pumping. This luminescence enhancement is explained by the formation of additional channels of transfer of external excitation by silicon nanocrystallites in porous silicon to impurity ytterbium and erbium ions in tungsten-tellurite glass.

Luminescence and structure of nanosized inclusions formed in SiO2 layers under double implantation of silicon and carbon ions

Luminescent and structural characteristics of SiO2 layers exposed to double implantation by Si+ and C+ ions in order to synthesize nanosized silicon carbide inclusions have been investigated by the photoluminescence, electron spin resonance, transmission electron microscopy, and electron spectroscopy methods. It is shown that the irradiation of SiO2 layers containing preliminary synthesized silicon nanocrystals by carbon ions is accompanied by quenching the nanocrystal-related photoluminescence at 700–750 nm and by the enhancement of light emission from oxygen-deficient centers in oxide in the range of 350–700 nm. Subsequent annealing at 1000 or 1100°C results in the healing of defects and, correspondingly, in the weakening of the related photoluminescence peaks and also recovers in part the photoluminescence of silicon nanocrystals if the carbon dose is less than the silicon dose and results in the intensive white luminescence if the carbon and silicon doses are equal. This luminescence is characterized by three bands at ∼400, ∼500, and ∼625 nm, which are related to the SiC, C, and Si phase inclusions, respectively. The presence of these phases has been confirmed by electron spectroscopy, the carbon precipitates have the sp3 bond hybridization. The nanosized amorphous inclusions in the Si+ + C+ implanted and annealed SiO2 layer have been revealed by high-resolution transmission electron microscopy.

Filamentary model of bipolar resistive switching in capacitor-like memristive nanostructures on the basis of yttria-stabilised zirconia

A filamentary model of bipolar resistive switching has been developed for the Au/ZrO2(Y)/TiN/Ti memristive nanostructures by using kinetic Monte-Carlo approach for the migration of oxygen vacancies at the stages of electroforming, SET, and RESET processes observed experimentally in the current-voltage switching hysteresis. Statistics of the forming and switching voltages are collected and used to simulate current-voltage characteristics based on a simplified multi-filament model. It is demonstrated that both abrupt and gradual switching behaviours can be determined by the parameters of the statistical distribution of switching voltages of different conductive channels - filaments. The results can be used for the development of new-generation nonvolatile memory.

Resistive switching in Au/SiO x /TiN/Ti memristive structures with varied geometric parameters and stoichiometry of dielectric film

We have studied Au/SiOx/TiN/Ti memristive structures obtained by magnetron sputtering, which exhibit a reproducible resistive switching effect. The influence of the thickness and stoichiometry of SiOx layer and the area of Au electrode on the parameters of switching has been analyzed. The obtained results show evidence in favor of the filament model of resistive switching in SiOx films.

The effect of irradiation with H+ and Ne+ ions on resistive switching in metal–insulator–metal memristive structures based on SiO x

The effect of irradiation with H+ and Ne+ ions with an energy of 150 keV on memristive Au/SiOx/TiN/Ti structures, which were obtained by magnetron sputtering and exhibited a reproducible resistive switching effect, is studied. It is demonstrated that the low and high resistance states remain unchanged up to a dose of 1 × 1016 cm–2 in the case of irradiation with H+ ions and a dose of ~3 × 1015 cm–2 under irradiation with Ne+ ions. The obtained results demonstrate the high tolerance of parameters of the studied memristive structures to both ionizing radiation and displacement damage.