Phase change memory materials and their applications

Lazarenko P., Kovalyuk V., An P., Kozyukhin S., Takáts V., Golikov A., Glukhenkaya V., Vorobyov Y., Kulevoy T., Prokhodtsov A., Sherchenkov A., Goltsman G.

In the past years, Ge 2 Sb 2 Te 5 has been considered a promising functional material for a variety of reconfigurable multilevel devices, including photonic integrated circuits for the post-von Neumann arithmetic processing. However, despite significant advances, it is necessary to reduce the switching energy of Ge 2 Sb 2 Te 5 for creation of the on-chip low power all-photonic spiking neural networks. The present work focuses on the effect of tin ion implantation on the properties of amorphous Ge 2 Sb 2 Te 5 thin films, as well as on the performance of Mach-Zehnder interferometers and balanced beam splitters based on them. As a result, Sn-doping accompanied by the formation of weaker bonds in Ge 2 Sb 2 Te 5 thin films is an efficient approach to significantly reduce the threshold energy of fs-laser initiated phase transitions and change the effective absorption coefficient. The possibility of using the Sn-doped Ge 2 Sb 2 Te 5 thin films for fully optical multilevel reversible recording between 9 different levels (3 bits) has been demonstrated by experimental measurements of fabricated on-chip balanced beam splitters. The obtained results show that the Sn doping of Ge 2 Sb 2 Te 5 layer can be used to optimize the properties of the GST225 thin films, in particular to reduce the switching energy. So, it has the potential to improve the characteristics of reconfigurable multilevel nanophotonic devices using the GST225 thin films, including fully non-volatile memory and developed on-chip low power all-photonic circuits for post-von Neumann arithmetic processing.

Abdollahramezani S., Hemmatyar O., Taghinejad M., Taghinejad H., Krasnok A., Eftekhar A.A., Teichrib C., Deshmukh S., El-Sayed M.A., Pop E., Wuttig M., Alù A., Cai W., Adibi A.

Phase-change materials (PCMs) offer a compelling platform for active metaoptics, owing to their large index contrast and fast yet stable phase transition attributes. Despite recent advances in phase-change metasurfaces, a fully integrable solution that combines pronounced tuning measures, i.e., efficiency, dynamic range, speed, and power consumption, is still elusive. Here, we demonstrate an in situ electrically driven tunable metasurface by harnessing the full potential of a PCM alloy, Ge2Sb2Te5 (GST), to realize non-volatile, reversible, multilevel, fast, and remarkable optical modulation in the near-infrared spectral range. Such a reprogrammable platform presents a record eleven-fold change in the reflectance (absolute reflectance contrast reaching 80%), unprecedented quasi-continuous spectral tuning over 250 nm, and switching speed that can potentially reach a few kHz. Our scalable heterostructure architecture capitalizes on the integration of a robust resistive microheater decoupled from an optically smart metasurface enabling good modal overlap with an ultrathin layer of the largest index contrast PCM to sustain high scattering efficiency even after several reversible phase transitions. We further experimentally demonstrate an electrically reconfigurable phase-change gradient metasurface capable of steering an incident light beam into different diffraction orders. This work represents a critical advance towards the development of fully integrable dynamic metasurfaces and their potential for beamforming applications. The authors demonstrate an efficient platform for electrically driven reconfigurable metasurfaces by using Ge2Sb2Te5 to realize non-volatile, reversible, multilevel, and fast optical modulation and wavefront engineering in the near-infrared spectral range.

Kunkel T., Vorobyov Y., Smayev M., Lazarenko P., Romashkin A., Kozyukhin S.

Amorphous to crystalline phase transition in Ge 2 Sb 2 Te 5 film under the influence of a single femtosecond laser pulse is studied. Two-dimensional temperature calculations and kinetic model for crystallization were used to support experimental results and then to explain the fast mechanism of crystallization. Based on comparison with the experimental data, the theoretical Time-Temperature-Transformation diagram was calculated, that allowed to define the range of cooling rates at which crystallization is possible. The distribution of crystalline fraction in the thin film was calculated using these rates. Reflectance of the simulated structures turned out to be in good agreement with experimental observations. • Crystallization with single femtosecond laser pulse in Ge 2 Sb 2 Te 5 films was observed. • TTT diagram was calculated to determine critical cooling rate for crystallization. • Purely thermal simulation reproduces the experimental data quite well.

Zabotnov S., Kolchin A., Shuleiko D., Presnov D., Kaminskaya T., Lazarenko P., Glukhenkaya V., Kunkel T., Kozyukhin S., Kashkarov P.

Ge2Sb2Te5 based devices attract the attention of researchers due to wide opportunities in designing phase change memory. Herein, we studied a possibility to fabricate periodic micro- and nanorelief at surfaces of Ge2Sb2Te5 thin films on silicon oxide/silicon substrates under multi-pulse femtosecond laser irradiation with the wavelength of 1250 nm. One-dimensional lattices with periods of 1250 ± 90 and 130 ± 30 nm were obtained depending on the number of acted laser pulses. Emergence of these structures can be explained by plasmon-polariton generation and laser-induced hydrodynamic instabilities, respectively. Additionally, formation of the lattices whose spatial period is close to the impacted laser wavelength can be modelled by considering the free carrier contribution under intensive photoexcitation. Raman spectroscopy revealed both crystallization and re-amorphization of the irradiated films. The obtained results show a possibility to fabricate rewritable all-dielectric data-storage devices based on Ge2Sb2Te5 with the periodic relief.

Wang J., Chen S., Zhang L., Zhao X., Duan F., Chen H.

In this review, the present status of nanosilver sintering is adapted in detail. This review shows the current scholarly exploration and achievements in this field through the two aspects of manufacturing and reliability. The preparation of nanosilver particles, organic coating and sintering methods, microstructure and failure modules of sintered nanosilver layers are described in detail. Finally, prospects and dilemmas of nanosilver sintering technology as a connection material for semiconductor devices and the directions of future extensions are discussed.

Trofimov P.I., Bessonova I.G., Lazarenko P.I., Kirilenko D.A., Bert N.A., Kozyukhin S.A., Sinev I.S.

Laser-induced periodic surface structures (LIPSS) can be fabricated in virtually all types of solid materials and show great promise for efficient and scalable production of surface patterns with applications in various fields from photonics to engineering. While the majority of LIPSS manifest as modifications of the surface relief, in special cases, laser impact can also lead to periodic modulation of the material phase state. Here, we report on the fabrication of high-quality periodic structures in the films of phase-change material Ge2Sb2Te5 (GST). Due to considerable contrast of the refractive index of GST in its crystalline and amorphous states, the fabricated structures provide strong spatial modulation of the optical properties, which facilitates their applications. By changing the excitation laser wavelength, we observe the scaling of the grating period as well as transition between formation of different types of LIPSS. We optimize the laser exposure routine to achieve large-scale high-quality phase-change gratings with controllable period and demonstrate their reversible tunability through intermediate amorphization steps. Our results reveal the prospects of fast and rewritable fabrication of high-quality periodic structures for photonics and can serve as a guideline for further development of phase-change material-based optical elements.

Aryana K., Gaskins J.T., Nag J., Stewart D.A., Bai Z., Mukhopadhyay S., Read J.C., Olson D.H., Hoglund E.R., Howe J.M., Giri A., Grobis M.K., Hopkins P.E.

Phase change memory (PCM) is a rapidly growing technology that not only offers advancements in storage-class memories but also enables in-memory data processing to overcome the von Neumann bottleneck. In PCMs, data storage is driven by thermal excitation. However, there is limited research regarding PCM thermal properties at length scales close to the memory cell dimensions. Our work presents a new paradigm to manage thermal transport in memory cells by manipulating the interfacial thermal resistance between the phase change unit and the electrodes without incorporating additional insulating layers. Experimental measurements show a substantial change in interfacial thermal resistance as GST transitions from cubic to hexagonal crystal structure, resulting in a factor of 4 reduction in the effective thermal conductivity. Simulations reveal that interfacial resistance between PCM and its adjacent layer can reduce the reset current for 20 and 120 nm diameter devices by up to ~ 40% and ~ 50%, respectively. These thermal insights present a new opportunity to reduce power and operating currents in PCMs. Designing efficient, fast and low power consumption phase change memories remains a challenge. Aryana et al. propose a strategy to reduce operating currents by manipulating the interfacial thermal resistance between the phase change unit and the electrodes without incorporating additional insulating layers.

Kraft N., Wang G., Bryja H., Prager A., Griebel J., Lotnyk A.

Ge-Sb-Te alloys are promising materials for non-volatile memory applications. Alloying of the materials with various elements is considered as prospective approach to enhance material properties. This work reports on the preparation and characterization of pure Ge-Sb-Te-O (GSTO) and alloyed with La-Sr-Mn-O (LSMO) thin films. Thermal heating of amorphous thin films to different temperatures show distinct crystallization behavior. A general trend is the decrease in the size of GSTO crystallites and the suppression in the formation of stable trigonal GSTO phase with increasing content of LSMO. Microstructural studies by transmission electron microscopy show the formation of metastable GSTO nanocrystallites dispersed in the amorphous matrix. Analysis of local chemical bonding by X-ray spectroscopy reveal the presence of different oxides in the GSTO-LSMO composites. Moreover, the composites with a high LSMO content exhibit higher crystallization temperature and significant larger sheet resistance in amorphous and crystalline phase, while a memory device made of GSTO-LSMO alloy reveals bipolar switching and synaptic behavior. In addition, the amount of LSMO in GSTO-LSMO thin films influences their optical properties and band gap. Overall, the results of this work reveal the highly promising potential of GSTO-LSMO nanocomposites for data storage and reconfigurable photonic applications as well as neuro-inspired computing.

Kunkel T., Vorobyov Y., Smayev M., Lazarenko P., Veretennikov V., Sigaev V., Kozyukhin S.

The nature of crystallization in telluride based phase change memory materials is being actively discussed, and we present new experimental results on the effect of a pulsed laser treatment on the amorphous thin film crystallization of composition Ge 2 Sb 2 Te 5 (GST225). It is shown that there are two ways of crystalline phase formation under femtosecond pulses excitation. At the moderate value of laser fluence, crystalline fraction forms inside the solid amorphous phase. This process is apparently two-stage, and this leads to formation of fine-grained polycrystalline material. The second way of crystallization proceeds at higher levels of the laser fluence, closer to the beam axis. In this case, larger grains are produced closer to the beam axis, and eventually no new nuclei can be formed due to high cooling velocity leading to inhibition of nucleation. The article also presents the results on the effect of the substrate type (metallic or oxide) and film thickness on crystallization, which is due to the light penetration depth and reflection from the film-substrate interface. • Threshold value of laser fluence for crystallization depends on the number of pulses. • Two types of Ge 2 Sb 2 Te 5 crystallization under femtosecond laser pulses are shown. • Both conductive and dielectric substrates could promote or inhibit crystallization. • Initial laser pulses provide incubation of crystalline nuclei.

Fedyanina M.E., Lazarenko P.I., Vorobyov Y.V., Kozyukhin S.A., Dedkova A.A., Yakubov A.O., Levitskii V.S., Sagunova I.V., Sherchenkov A.A.

Abstract—Extensive studies of Ge2Sb2Te5 material are associated with the possibility of producing multilevel nonvolatile elements for high-speed integrated optical functional circuits. The principle of multilevel recording in such devices is based on the formation of partially crystallized regions with substantially different optical properties in Ge2Sb2Te5 thin films. To predict the parameters of the effect initiating phase transformations and to reliably provide a reversible transition between many logic states, it is necessary to have reliable data on the optical characteristics of Ge2Sb2Te5 thin films in states with different degrees of crystallinity and on the conditions of attainment of such states. In the study, the influence of the phase state of Ge2Sb2Te5 films on the extinction coefficient and refractive index and variations in the optical band gap in relation to the temperature of heat treatment are investigated. Ge2Sb2Te5 thin-film samples are examined by means of atomic-force microscopy, X-ray phase analysis, and energy-dispersive microanalysis to determine the film thickness, morphology, phase state, and composition. By spectroscopic ellipsometry, the spectra of the ellipsometric angles ψ and Δ (the amplitude and phase components of the light wave) are obtained, and the extinction coefficient and refractive index are determined. The influence of the layer models and mathematical models on calculation of the dispersions of the optical parameters of Ge2Sb2Te5 films is considered. A substantial increase in the extinction coefficient and refractive index at the wavelength 1550 nm on heat treatment at temperatures higher than 200°С is established. It is shown that the optical band gaps of Ge2Sb2Te5 thin films in the amorphous and crystalline states are 0.71 and 0.47 eV, respectively. It is found that the dependences of the extinction coefficient, refractive index, and band gap on the degree of crystallinity of Ge2Sb2Te5 thin films are close to linear.

Tiwari S.C., Kalia R.K., Nakano A., Shimojo F., Vashishta P., Branicio P.S.

Phase-change materials are of great interest for low-power high-throughput storage devices in next-generation neuromorphic computing technologies. Their operation is based on the contrasting properties of their amorphous and crystalline phases, which can be switched on the nanosecond time scale. Among the archetypal phase change materials based on Ge-Sb-Te alloys, Sb2Te3 displays a fast and energy-efficient crystallization-amorphization cycle due to its growth-dominated crystallization and low melting point. This growth-dominated crystallization contrasts with the nucleation-dominated crystallization of Ge2Sb2Te5. Here, we show that the energy required for and the time associated with the amorphization process can be further reduced by using a photoexcitation-based nonthermal path. We employ nonadiabatic quantum molecular dynamics simulations to investigate the time evolution of Sb2Te3 with 2.6, 5.2, 7.5, 10.3, and 12.5% photoexcited valence electron-hole carriers. Results reveal that the degree of amorphization increases with excitation, saturating at 10.3% excitation. The rapid amorphization originates from an instantaneous charge transfer from Te-p orbitals to Sb-p orbitals upon photoexcitation. Subsequent evolution of the excited state, within the picosecond time scale, indicates an Sb-Te bonding to antibonding transition. Concurrently, Sb-Sb and Te-Te antibonding decreases, leading to formation of wrong bonds. For photoexcitation of 7.5% valence electrons or larger, the electronic changes destabilize the crystal structure, leading to large atomic diffusion and irreversible loss of long-range order. These results highlight an ultrafast energy-efficient amorphization pathway that could be used to enhance the performance of phase change material-based optoelectronic devices.

Luong M.A., Wen D., Rahier E., Ratel Ramond N., Pecassou B., Le Friec Y., Benoit D., Claverie A.

Cao T., Wang R., Simpson R.E., Li G.

The ultrafast, reversible, nonvolatile and multistimuli responsive phase change of Ge-Sb-Te (GST) alloy makes it an interesting “smart” material. The optical features of GST undergo significant variation when its state changes between amorphous and crystalline, meaning that they are useful for tuning photonic components. A GST phase change material (PCM) can be efficiently triggered by stimuli such as short optical or electrical pulses, providing versatility in high-performance photonic applications and excellent capability to control light. In this review, we study the fundamentals of GST-tuned photonics and systematically summarise the progress in this area. We then introduce current developments in both GST-metal hybrid metamaterials and GST-based dielectric metamaterials, and investigate the strategy of designing reversibly switchable GST-based photonic devices and their advantages. These devices may have a vast array of potential applications in optical memories, switches, data storage, cloaking, photodetectors, modulators, antennas etc. Finally, the prospect of implementing GST PCM in emerging fields within photonics is considered.

Bourgine A., Grisolia J., Vallet M., Benoit D., Le Friec Y., Caubet-Hilloutou V., Claverie A.

Ge-rich GeSbTe (GST) alloys are attracting Phase Change Materials for future memories as their higher crystallization temperature offers an extended range of applications. We have studied the electrical characteristics of PCM cells using such alloys as active layers. We show by impedance spectroscopy that the cells in the RESET (amorphous) state are not only resistive but also exhibit a capacitive component. Although trap-assisted conduction models are apparently able to describe the I(V) and I(T) characteristics of the devices in this state, their physical background is thus questionable. Alternatively, we show that granular models, describing electrical transport through conductive grains separated by insulating interfaces, are also able to simulate these characteristics, while fed by physically sound fitting parameters. Moreover, we show that the SET (crystalline) state is not simply ohmic but that its characteristics, as conductive as a metal but reacting as an insulator to temperature, resemble to those found in a semiconductor doped with a very low ionization energy defect. Finally, all these characteristics can be understood by considering that the electrical properties of cells made of Ge-rich GST layers are not those characteristic of some defective and homogeneous material but instead result from strong chemical heterogeneities found both in the amorphous and crystalline states of these Ge-rich alloys.

Zalden P., Koch C., Paulsen M., Esters M., Johnson D.C., Wuttig M., Lindenberg A.M., Bensch W.

Baranowski J., Mroz B., Mielcarek S., Iatsunskyi I., Trzaskowska A.

High-resolution Brillouin spectroscopy was employed to investigate the anisotropy in surface wave velocities within a bulk single crystal of Sb2Te3, a well-known layered van der Waals material. By leveraging the bulk elastic constants derived from various simulation methods, we were able to theoretically calculate the distribution of surface acoustic phonon velocities on the cleavage plane of the material. Upon analyzing multiple simulation results, it became evident that the most significant discrepancies arose in the calculations of the elastic constant c33, with values ranging from 48 to 98 GPa. Consequently, a direct measurement of the c33 elastic constant for Sb2Te3 was attempted. Through our ellipsometry results, we determined both the real and imaginary components of the refractive index, leading to an experimental determination of the c33 elastic constant, which was found to be 47.9 GPa. Additionally the results of the conducted studies enabled the analytical determination of all components of the elastic property tensor of the investigated material.

Budagovsky I.A., Smirnov P.A., Zolot’ko A.S., Lazarenko P.I., Smayev M.P.

Phase-change materials are very interesting and promising objects for various optical applications due to simple and high-speed switching between the amorphous and crystalline states. In this study, we consider the specific features of laser crystallization and ablation of thin amorphous Ge2Sb2Te5 films exposed to the HG01 (Hermite–Gaussian TEM01) mode of cw visible light. This exposure led to two-zone crystallization or ablation, depending on the laser intensity. Microscale two-zone ablation made it possible to observe Young’s fringes for the radiation transmitted through a sample, as in the case of two-point-source interference. This approach is promising for express analysis of the laser beam profile.

Glukhenkaya V.B., Pestov G.N., Gulidova A.I., Saurov M.A., Smirnov P.A., Fedyanina M.E., Kozlov A.O., Savitskiy A.I.

Thin films of Ge2Sb2Te5 (GST) material are characterized by a high phase-transformation rate (<50 ns) and optical contrast (~30%) between amorphous and crystalline structures. A common way to switch GST thin films between the amorphous and crystalline states is laser radiation. However, the reversible switching of large elements of a GST functional area can only be implemented in the surface scanning mode with a pulsed laser beam, which significantly increases the switching time. This paper presents a design for switching a microscale GST functional area by means of a thin-film resistive-heating element. It is found that the crystallization of a GST functional area with a size of 100 × 100 μm and thickness of 30 nm into the face-centered cubic (fcc) structure occurs when passing a single electric pulse with a duration of 200 ms and an amplitude of 2.1 V (~310 mA) through the heating element or at a voltage of 1.7 V and a current of ~220 mA in the DC measurement mode. According to computer modeling, under this electrical action, the GST area heats up to a temperature of ~218°C. The results obtained demonstrate the possibility of using the developed and manufactured structure for creating elements of nonvolatile active optical and optoelectronic devices, including information displays.

Zhu L., Cai Q., He X., Liu L., Lai T., Zhang M., Wang Z.

Tolepov Z., Prikhodko O., Kolobov A., Ismailova G., Peshaya S., Guseinov N., Mukhametkarimov Y., Kapanov A., Maksimova S.

Smayev M.P., Smirnov P.A., Budagovsky I.A., Fedyanina M.E., Glukhenkaya V.B., Romashkin A.V., Lazarenko P.I., Kozyukhin S.A.

Chalcogenide phase-change materials are promising for optical technologies, since they allow rapid (tens of nanoseconds) reversible switching between the amorphous and crystalline phase states characterized by significantly different electrical and optical parameters. In this work we experimentally studied the local optical transition of as-deposited amorphous Ge2Sb2Te5 thin films into the crystalline state under the action of structured continuous-wave laser beams. For cylindrical laser beams with an annular intensity profile obtained through the phase singularity or through the axially symmetric polarization distribution, significantly more efficient crystallization was observed in comparison with the commonly used fundamental Hermite–Gaussian HG00 mode. The numerical simulation showed that the annular intensity distribution results in a more uniform temperature profile inside the irradiated region, which is necessary for more uniform crystallization. To analyze the degree of crystallinity we used Raman spectroscopy and optical microscopy, enhanced with digital brightness filtering for characterization of the reflectance within the modified region.

He A., Zhu J., Wang G., Lotnyk A., Cremer S., Chen Y., Shen X.

A single Sb phase demonstrates potential for use in phase change memory devices. However, the rapid crystallization of Sb at room temperature imposes limitations on its practical application. To overcome this issue, Sb is alloyed with Se using a reactive co-sputtering deposition technique, employing both Sb and Sb2Se3 sputter targets. This process results in the formation of Sb-rich Se thin films with varying compositions. Compared to pure Sb, the Sb-rich Se thin films exhibit enhanced thermal stability due to the formation of Sb–Se bonds and reduced resistance drift. In particular, the Sb86.6Se13.4 thin film demonstrates an exceptionally low resistance drift coefficient (0.004), a high crystallization temperature (Tc = 195 °C), a high 10-year data retention temperature (116.3 °C), and a large crystallization activation energy (3.29 eV). Microstructural analysis of the Sb86.6Se13.4 reveals the formation of a trigonal Sb phase with (012) texture at 250 °C, while Sb18Se and Sb2Se3 phases form at 300 °C. Conversely, the Sb98.3Se1.7 thin film shows the formation of the single Sb phase with (001) texture, a Tc of 145 °C, and a low resistance drift coefficient (0.011). Overall, this study demonstrates that the alloying strategy is a viable approach for enhancing thermal stability and reducing resistance drift in Sb-based phase-change materials.

Rempel Andrey A., Ovchinnikov Oleg V., Weinstein Ilya A., Rempel Svetlana V., Kuznetsova Yulia V., Naumov Andrei V., Smirnov Mikhail S., Eremchev Ivan Yu., Vokhmintsev Alexander S., Savchenko Sergey S.

Quantum dots are the most exciting representatives of nanomaterials. They are synthesized using advanced methods of nanotechnology pertaining to both inorganic and organic chemistry. Quantum dots possess unique physical and chemical properties; therefore, they are used in very different fields of physics, chemistry, biology, engineering and medicine. It is not surprising that the Nobel Prize in chemistry in 2023 was given for discovery and synthesis of quantum dots. This review addresses modern methods for the synthesis of quantum dots and their optical properties and practical applications. In the beginning, a short insight into the history of quantum dots is given. Many gifted scientists, including chemists and physicists, were engaged in these studies. The synthesis of quantum dots in solid and liquid matrices is described in detail. Quantum dots are well-known owing to their unique optical properties; that is why the attention in the review is focused on the quantum-size effect. The causes for fascinating blinking of quantum dots and techniques for observation of a single quantum dot are considered. The last part of the review describes mportant applications of quantum dots in biology, medicine and quantum technologies.The bibliography includes 772 references.

Korolev V., Sinelnik A.D., Rybin M.V., Lazarenko P., Kushchenko O.M., Glukhenkaya V., Kozyukhin S., Zuerch M., Spielmann C., Pertsch T., Staude I., Kartashov D.

Abstract High-order harmonic generation (HHG) in solids opens new frontiers in ultrafast spectroscopy of carrier and field dynamics in condensed matter, picometer resolution structural lattice characterization and designing compact platforms for attosecond pulse sources. Nanoscale structuring of solid surfaces provides a powerful tool for controlling the spatial characteristics and efficiency of the harmonic emission. Here we study HHG in a prototypical phase-change material Ge2Sb2Te5 (GST). In this material the crystal phase can be reversibly changed between a crystalline and amorphous phase by light or electric current mediated methods. We show that optical phase-switching is fully reversible and allows for dynamic control of harmonic emission. This introduces GST as new addition to materials that enable flexible metasurfaces and photonic structures that can be integrated in devices and allow for ultrafast optical control.

Yuan Y., He L., Qian J., Song S., Song Z., Liu R., Zhai J.

L’vov P.E., Sibatov R.T., Ryazanov R.M., Novikov D.V.

Based on the phase-field theory, a two-dimensional model describing the formation and growth of filaments in a system of conducting particles immersed in a dielectric matrix with active electrodes has been developed. We simulate and analyze the dynamics of redistribution of active substance, which undergoes reversible intercalation through the particle surface and forms conductive phase within the matrix. This phase corresponds to the filaments connecting particles either to each other or to the electrodes. It has been demonstrated that the system exhibits hysteresis in current–voltage curves observed under conditions of sawtooth-like variation of the electrical current. In the proposed model, the primary mechanism for the formation and growth of filaments is the non-uniform distribution of conductivity throughout the system, resulting in the formation of a highly non-uniform electric field. This non-uniform electric field may lead to the movement of fragments of the conductive phase, corresponding to the extraction of filaments from the particles or active electrodes. Experimental investigations of percolation network of silver nanoparticles in a HfOx dielectric matrix are presented. The results reveal that even when a percolation ensemble of silver nanoparticles is coated with hafnium oxide, memristive effects remain preserved. Additionally, the practical use of the phase-field model is demonstrated, as it qualitatively reproduces the memristive dynamics observed in percolation ensembles of nanoparticles. This model takes into account the concurrent evolution of phases and the redistribution of electric voltages within the sample. The findings can have important implications for understanding and manipulating memristive behavior in nanoparticle-based systems with potential applications in neuromorphic computations.

Tolkach N.M., Vishnyakov N.V., Litvinov V.G., Sherchenkov A.A., Trusov E.P., Glukhenkaya V.B., Pepelyaev D.V.

Phase-transition materials, in particular chalcogenide glassy semiconductors and Ge–Sb–Te system materials, are of interest for application in optical information-processing technologies. The uniqueness of these materials lies in the fact that they have a low-energy, and fast and reversible phase transition, which leads to a significant change in the refractive index in the infrared region of the optical spectrum. The model calculations carried out in the work make it possible to investigate the transformation of the optical properties in multilayer structures consisting of SiO2, Si, Si3N4 layers and the active layer of a phase transition material when its phase state changes. The aim of these studies is to fulfill the condition of the lowest optical losses during the transmission and reflection of radiation of 1550 nm in such structures in the case of amorphous and crystalline states of the active layer, respectively. As a result, a nine-layer structure “SiO2//111 nm Si/277 nm SiO2/ 111 nm Si/251 nm SiO2/10 nm Ge2Sb2Se4Te/241 nm SiO2/110 nm Si/276 nm SiO2/112 nm Si//SiO2”, which satisfies the specified conditions to the greatest degree, is designed.

Lebedeva Y.S., Smayev M.P., Budagovsky I.A., Fedyanina M.E., Sinev I.S., Kunkel T.S., Romashkin A.V., Smirnov P.A., Sherchenkov A.A., Kozyukhin S.A., Lazarenko P.I.

The photoinduced crystallization of thin amorphous films based on the binary compound Sb2Se3 and the ternary compound Ge2Sb2Te5 under continuous-wave laser irradiation is studied. The optical parameters of amorphous and crystalline films are analyzed by optical and atomic force microscopies, ellipsometry, spectrophotometry, and Raman spectroscopy. The crystallization temperatures, optical band gaps, Urbach-tail lengths, the activation energies of electrical conductivity, as well as the spectral dependences of the refractive indices and the extinction coefficients, are determined. The crystallized regions of Sb2Se3 are characterized by the more pronounced inhomogeneity of reflectivity (grain size) compared to crystalline regions of Ge2Sb2Te5 produced with the same laser-beam parameters. An analysis of the topography of crystallized films shows qualitative differences in the crystallite sizes. The distinctions may be related to differences in the mechanism of photoinduced crystallization. The Sb2Se3 compound has a higher optical band gap in comparison with Ge2Sb2Te5 and lower absorbance in the visible and near-infrared region, which can reduce the optical losses in the elements of silicon integrated optics based on the phase-change materials, as well as extend the range of possible application of phase-change materials for optical elements and nanophotonics devices.

Zabotnov S.V., Kashkarov P.K., Kolobov A.V., Kozyukhin S.A.

Abstract Chalcogenide vitreous semiconductors (ChVSs) are of both fundamental and applied interest as materials in which reversible structural transformations within the amorphous phase and phase transitions to the crystalline state can be effectively implemented and various microstructures and nanostructures can be obtained as a result of external effects. One of the most promising methods for such ChVS modifications is the pulsed-laser-irradiation technique, which is a noncontact technology of local impact and makes it possible to change the structural, optical, and electrical properties of samples in a wide range. This includes methods based on the precision formation of a surface microrelief and nanorelief, and high contrast in the conductivity and refractive index between the crystalline and amorphous phases. This work reviews key publications on the structural modification of thin films from the most widely studied binary and ternary ChVS compounds (As2S3, As2Se3, Ge2Sb2Te5, etc.) to show the use of irradiated samples as metasurfaces for photonic applications and promising phase-change data storage.

Kovalyuk V., Sheveleva E., Mel’nikov A., Auslender M., Goltsman G., Shneck R., Dashevsky Z.

PbTe-based compounds are excellent candidates for the different types of optical detector applications from near to far IR ranges. In the present work, a technology has been developed for the fabrication of Pb1−xSnxTe compositions, doped with In, on a thin amorphous substrate (polyimide). The film preparation was performed by the electron gun evaporation method. The systematic study of structure and transport properties (Hall coefficient and electric conductivity) in the entire temperature range of 10–300 K for Pb1−xSnxTe:In films (x=0, 0.1, 0.2) was investigated. It was studied that the photoconductivity of the films in the telecom wavelength range, including kinetics, sensitivity, and noise equivalent power, has been conducted and it discovered persistent photoconductivity for all compositions at the temperature T&lt;21 K. The results of the work have promising potential to use poly(nano) crystalline Pb1−xSnxTe:In films on an amorphous substrate both for photodetection in the telecom wavelength range and for the creation of all-optical neuromorphic systems, cooled memory, and logic elements operating at the low energy of laser pulses.