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The electrophysical characteristics of a multilayer memristive Au/Ta/ZrO2(Y)/TaOx/TiN structure have been studied. Electron and ion electret effects due to charge carrier trapping and ion migration polarization in the dielectric have been discovered. The influence of traps on electroforming processes and resistive switching has been established. The values of activation energy and ion and trap concentrations have been determined. The effect of resistive switching stabilization has been found, which is associated with the specific bilayer structure of TaOx and self-forming tantalum nanoclusters. The nanoclusters serve as electric field concentrators in the course of electroforming and subsequent resistive switching.

We have studied the resistive switching in memristive structures based on 40-nm-thick yttria-stabilized zirconia (YSZ) films exposed to 6-keV Si+ ion irradiation to a total dose of 5.4 × 1015 cm–2. It is established that the ion irradiation leads to increased stability of the parameters of resistive switching in YSZ based memristive structures. This effect is related to the fact that the diameter of conducting filaments in irradiated structures is limited by lateral dimensions of the region of atomic displacement cascades (i.e., the region occupied by point defects produced by bombarding ions). The oxidation of ion-modified filaments during resistive switching proceeds more effectively and leads to increasing resistance in the high-resistance state of memristive structures.

The stochastic resonance phenomenon has been studied experimentally and theoretically for a state-of-art metal-oxide memristive device based on yttria-stabilized zirconium dioxide and tantalum pentoxide, which exhibits bipolar filamentary resistive switching of anionic type. The effect of white Gaussian noise superimposed on the sub-threshold sinusoidal driving signal is analyzed through the time series statistics of the resistive switching parameters, the spectral response to a periodic perturbation and the signal-to-noise ratio at the output of the nonlinear system. The stabilized resistive switching and the increased memristance response are revealed in the observed regularities at an optimal noise intensity corresponding to the stochastic resonance phenomenon and interpreted using a stochastic memristor model taking into account an external noise source added to the control voltage. The obtained results clearly show that noise and fluctuations can play a constructive role in nonlinear memristive systems far from equilibrium.

Resistive switching and adaptive behavior of resistive state in response to electrical stimulation has been studied for the silicon oxide based memristive devices subjected to electroforming in the conditions of current compliance in comparison with the analogous memristive devices after electroforming without any current limitation. The limitation of current and temperature during electroforming affects the parameters of growing conductive filament ensembles and reduction-oxidation reactions resulting in a gradual character and a wide dynamic range of resistance change important for neuromorphic applications.

The effect of boron implantation on the light-emitting properties of dislocation structures formed in silicon by Si+ ion implantation with subsequent annealing is studied. It is shown that the implantation of B+ ions has a significant effect on the dislocation-related luminescence intensity, spectrum and the temperature dependence of the D1-band intensity. It is found that the temperature dependence is nonmonotonous and involves two regions, in which the D1-band intensity increases with increasing temperature and has two well-pronounced maxima at 20 K and 60–70 K. The maximum at 20 K is associated with the morphological features of the dislocation structure under study, whereas the maximum at 60–70 K is associated with the additional implantation of the boron impurity into the dislocation region of the samples. It is established that the intensities of the experimentally observed maxima and the position of the high-temperature maximum depend on the implanted boron concentration.

Gallium oxide nanocrystals encapsulated in Al2O3 film on a Si substrate have been synthesized by using ion implantation followed by thermal annealing at 800 °C or 900 °C. Formation of $\beta $ -Ga2O3 nanocrystals is confirmed by transmission electron microscopy. The photoresponse of a photodetector fabricated on the implanted layer by the deposition of interdigitated electrode pattern is estimated by analyzing the current–voltage characteristics. The ratio of photocurrent at the wavelength of 250 nm and a voltage of 4 V to dark current around ~15 is found for the sample annealed at 900 °C. The spectral dependence of photoresponse for this sample demonstrates excellent solar-blind ultraviolet characteristics in the wavelength range of 250–270 nm with a rejection ratio 42 at the bias of 1 V. At the bias of 4 V, the responsivity of 50 mA/ $\mu \text{W}$ upon illumination at 250 nm and a cutoff at 280 nm are observed for the 900 °C annealing. The sample annealed at 800 °C shows lower ultraviolet responsivity due to the high density of defects. The data are analyzed in relation to the generation of carriers in Ga2O3 nanocrystals and their transport in the damaged Al2O3 matrix. The reported results pave the way toward the fabrication of next generation high sensitive solar-blind photodetectors.

Bipolar resistive switching of the metal-insulator-semiconductor (MIS) capacitor-like structures with the inert Au top electrode and Si3N4 dielectric nanolayer (6 nm thick) has been investigated. The effect of highly doped n+-Si substrate is revealed related to the changes in semiconductor space charge region on the small-signal parameters of parallel and serial equivalent circuit models measured in the high- and low-resistive capacitor states, as well as under laser illumination. The increase in conductivity of semiconductor capacitor plate significantly reduces the charging and discharging times of capacitor-like structures.

A physical model of synaptically coupled neuron-like generators interacting via a memristive device has been presented. The model simulates the synaptic transmission of pulsed signals between brain neurons. The action on the receiving generator has been performed via a memristive device that demonstrates adaptive behavior. It has been established that the proposed coupling channel provides the forced synchronization with the parameters depending on the memristive device sensitivity. Synchronization modes 1: 1 and 2: 1 have been experimentally observed.

The change of the immitance of the metal–insulator–metal memristive structures based on SiOx, which is observed during electroforming and resistive switching, confirms the formation of conducting channels (filaments) in the insulator during forming and their rupture upon a transition of the structure to a highresistance state. The observed switching of the differential capacitance and conductivity synchronously with the switching of current (resistance) can substantially extend the functional applications of memristive devices of this type.

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 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.

Transmission electron-microscopy examination revealed the appearance of a hexagonal silicon (9R polytype) inclusions in the subsrface silicon layer upon ion implantation and subsequent heat treatment of the SiO2/Si structure. The formation of this hexagonal phase is stimulated by mechanical stresses arising in the heterophase system in the course of ion implantation.

The search of ways to improve light-emitting properties of silicon is of great importance for modern optoelectronics. In this work, the photoluminescence (PL) properties of the band at λ = 1235 nm, which appears in silicon upon irradiation of the SiO2/Si system with Kr+ ions followed by annealing at 800 °C, have been studied. It is assumed that the source of PL is a 9R-Si hexagonal phase formed in Si substrate at the interface with SiO2 film. An interpretation is given for the established PL regularities that include the dependencies of PL band intensity on temperature and laser excitation power, as well as the temperature dependence of spectral position of the band maximum.

An original approach has been presented to model the regularities and parameters of resistive switching based on the kinetic Monte Carlo (kMС) 3D simulation of stochastic migration of oxygen vacancies/ions in metal-oxide memristive devices promising for applications in emerging nonvolatile memory, in-memory and neuromorphic computing systems. The efficiency and flexibility of the approach is demonstrated by the examples of experimentally realized Au/oxide/TiN memristive device structures, in which yttria-stabilized zirconia (ZrO2(Y)) polycrystalline films and amorphous SiO x columnar films obtained by magnetron sputtering are used as the switching oxide material. The proposed approach combines the universal kMС framework for ion migration and relatively simple physics-based methods for taking into account additional factors related to the structure and morphology of specific oxide material, interface phenomena and energetics of electronic processes, and therefore does not require time-consuming calculations and is not critical to the computing power.

The formation of a topological structure in thin films of the high-temperature superconductor YBa2Cu3O7–δ (YBCO) using ion implantation is studied. The crystal structure and electrical properties of the initial film and the formed insulating regions are investigated. The critical temperature and critical current are measured for microbridges with a width of 3–50 μm fabricated by ion implantation. The results indicate the effectiveness of the ion-implantation method for manufacturing topological structures in YBCO films.

An array of cross-point memristive devices has been implemented on the basis of yttria-stabilized zirconia thin film for applications in prototypes of spiking neural networks. The resistive switching phenomena and the plasticity nature of such memristive devices are studied. Reproducible bipolar resistive switching and precise tuning of resistive state are demonstrated and used to implement the plasticity rule according to STDP (spike-timing-dependent plasticity) mechanism. STDP learning is found to be dependent on the memristor's initial resistive state value and discussed in terms of the finite conductance change in studied structures. Obtained results provide the foundation for autonomous neuromorphic circuits with unsupervised learning development.

Light-emitting layers of hexagonal 9R silicon were synthesized by ion implantation into SiO2/Si substrates. Using cross-sectional transmission electron microscopy, the formation of a 9R phase in a cubic silicon substrate near the interface with silicon dioxide under irradiation with Kr+ ions (80 keV) and subsequent annealing at 800 °C is demonstrated. Arguments explaining how the new phase is formed through hexagonalization of the initial cubic silicon are presented. The synthesized 9R-Si layers are characterized by a low-temperature photoluminescence line with the maximum at a wavelength around 1240 nm. First-principles calculations of the 9R-Si electronic band structure showed that this material is an indirect-gap semiconductor with the bandgap value of 1.06 eV, which is in good agreement with the spectral position of the experimentally observed photoluminescence line. Believing that the proposed approach can be extended to other semiconductors, we calculated the electronic band structure of 9R germanium and predicted that the hexagonalization converts cubic Ge into a direct-gap semiconductor with the bandgap of 0.48 eV.Light-emitting layers of hexagonal 9R silicon were synthesized by ion implantation into SiO2/Si substrates. Using cross-sectional transmission electron microscopy, the formation of a 9R phase in a cubic silicon substrate near the interface with silicon dioxide under irradiation with Kr+ ions (80 keV) and subsequent annealing at 800 °C is demonstrated. Arguments explaining how the new phase is formed through hexagonalization of the initial cubic silicon are presented. The synthesized 9R-Si layers are characterized by a low-temperature photoluminescence line with the maximum at a wavelength around 1240 nm. First-principles calculations of the 9R-Si electronic band structure showed that this material is an indirect-gap semiconductor with the bandgap value of 1.06 eV, which is in good agreement with the spectral position of the experimentally observed photoluminescence line. Believing that the proposed approach can be extended to other semiconductors, we calculated the electronic band structure of 9R germaniu...

Bipolar resistive switching in metal-insulator-semiconductor (MIS) capacitor-like structures with an inert Au top electrode and a Si3N4 insulator nanolayer (6 nm thick) has been observed. The effect of a highly doped n +-Si substrate and a SiO2 interlayer (2 nm) is revealed in the changes in the semiconductor space charge region and small-signal parameters of parallel and serial equivalent circuit models measured in the high- and low-resistive capacitor states, as well as under laser illumination. The increase in conductivity of the semiconductor capacitor plate significantly reduces the charging and discharging times of capacitor-like structures.

With the aim to establish the possibility of synthesis of GaN inclusions by co-implantation of Ga and N ions in silicon and SiO2 films on a silicon substrate, the chemical composition and photoluminescence of implanted layers have been investigated. It is observed that the heavy loss of implanted atoms occurs owing to the out-diffusion (Ga from Si, and Ga and N from SiO2) in the process of post-implantation annealing. Preliminary implantation of nitrogen to form silicon nitride or oxynitride layers is shown to reduce the degree of impurity losses. In the photoluminescence spectrum of both Si and SiO2 subjected to Ga and N co-implantation, the band at 530-550 nm is present, which can be related to 'defect' luminescence of GaN.

The response to electrical pulses of various parameters has been studied for the CMOS-compatible memristive nanostructures on the basis of silicon oxide demonstrating reproducible resistive switching. It is established that an increase in the amplitude or width of a single programming pulse is followed by the gradual decrease in the device resistivity. By applying periodic pulse sequences of different polarity it is possible to obtain both lower and higher resistance states. This adaptive behavior is analogous to synaptic plasticity and considered as one of the main conditions for the application of memristive devices in neuromorphic systems and synaptic electronics.

Using the envelope-function approximation, the single-particle states of electrons and holes in spherical GaN nanocrystals embedded in different amorphous dielectric matrices (SiO2, Al2O3, HfO2 and Si3N4) have been calculated. Ground state energies of electrons and holes in GaN nanocrystals are determined using the isotropic approximation of the k ⋅ p -Hamiltonian. All the ground state energies are found to increase with lowering the nanocrystal size and are proportional to the R−n, where R is the nanocrystal radius, n =1.5-1.9 for electrons and 1.7-2.0 for holes. The optical gap of GaN nanocrystals changes from 3.8 to 5 eV for the nanocrystal radius ranging from 3 to 1 nm.