Home – Home – Jornals – Avtometriya 2022 number 6

The emergence of magnetic properties in nano-objects of non-magnetic substances based on silicon and transition metal (iron) is considered. An analysis of the literature showed that, for a monolayer iron coating on a vicinal silicon surface with (111) orientation after solid-phase annealing at 450-550 °C, a system of self-ordered two-dimensional nanorods with the α-FeSi₂ structure is formed, which has superparamagnetic properties. In this work, we study the transition to ferromagnetic properties in a system of α-FeSi₂ nanorods in the temperature range of 2-300 K with an increase in the iron coverage to 5.22 monolayers, which is important for creating spintronics devices in the framework of the planar silicon technology.

Structural, electric, and optical studies of silicon-on-sapphire substrates with silicon and hafnia nanolayers have been carried out depending on the substrate thickness. It is shown that the biaxial tensile stress induced in the intermediate HfO₂ layer - as a result of the heat treatment of such structures, due to the large difference in the thermal expansion coefficients between the layers of silicon, sapphire and hafnium dioxide, - stimulates the current hysteresis in the SOS-pseudo-MOSFET channel. It is found that a decrease in the mechanical stress in hafnium dioxide leads to an increase in the coercive field and ferroelectric switching at low fields in hafnia nanolayers.

Layered SnSe₂ 50 and 30 nm thick films are grown using in situ reflection electron microscopy on Si(111) and Bi₂Se₃(0001) substrates. The growth of films proceeds by a multilayer mechanism with the formation of pronounced mounds. The height of the atomic steps is measured by atomic force microscopy (AFM) and amounts to 0.6 nm, which corresponds to the thickness of the SnSe₂ layer. The ex situ AFM image of the SnSe₂ film grown on Si(111) shows a high concentration of screw dislocations in the film (~12 μm^-2) and the presence of domains with triangular step faceting having two types of orientation with respect to the substrate. It has been found that the SnSe₂ growth on the single crystal Bi₂Se₃(0001) surface occurs with the formation of hexagonal-faceted mounds equally oriented with respect to the substrate. The mounds are formed by a multilayer mechanism both in the places where screw dislocations come to the surface and due to periodic nucleation of 2D islands on the highest terraces. The sizes of the highest terraces are up to 1 μm. The spectra characteristics of the films are obtained using the Raman scattering method on both substrates and correspond to the 1T-SnSe₂ phase in both cases.

An interband photoluminescence (PL) of structures with multiple quantum wells (MQWs) with different contents of Ge and Sn has been obtained. The peak position on the PL spectra obtained from Ge_0.93-xSi_xSn_0.07/Si MQWs is shifted to longer wavelengths with the Ge content increase in the solid solution and is observed in the energy range of 0,85-0.68 eV for the Ge content from 30 to 78%. Thus, the peak shift over the wavelength from 1,46 μm to 1,82 μm was observed, and the total spectral range of MQWs luminescence covered by these structures was 1,3-2,1 μm. An even more significant shift of the MQWs PL peak to the long wavelength region is achieved by increasing the Sn content. The increase in the Sn content from 7% to 14% at a constant 30% Ge content leads to the peak shift from 0,85 eV to 0,75 eV. A simultaneous increase in the content of both tin and germanium in the solid solution (to 14% and 79%, respectively) makes it possible to obtain the PL peak with the energy of 0,58 eV, which corresponds to the emission wavelength of 2,14 μm. A sharp “red” shift in the position of the PL peak with the temperature increase is found. Its value is up to 50 meV at the change of the heating sample temperature from 11 K to 60-80 K. Such a significant shift in the position of the MQWs PL peak is explained by the model assuming that charge carriers are randomly localized on spatial inhomogeneities of the MQWs at low temperatures, whereas they are redistributed and transferred to a thermodynamically equilibrium state with the lowest energy as the temperature increases.

The kinetics of reflectivity signals from nanostructures including an equal number of quantum wells with an identical composition In_xGa_1-xAs (x=0.32) with GaAs barriers of 2, 4, 6, and 8 monolayers grown over a semiconductor reflector under identical conditions are investigated by the pump-probe technique. The tendency of recovery time shortening for thinner barriers is found. The prospects of further research and practical application of quantum wells coupled via charge carrier tunneling are under consideration.

An analysis of the structure of as-deposited films of nonstoichiometric germanosilicate glasses and the transformation of their structure under annealing is carried out using the Raman spectroscopy and IR spectroscopy. It is shown that the structure of the films is stable up to a temperature of 350 ^oC; under annealing beginning from 400 ^oC, amorphous germanium clusters are formed in the films. On the basis of these films, metal-insulator-semiconductor structures are fabricated, and prospects for their use in memristors and photodetectors are demonstrated.

This work demonstrates that digital technologies can be successfully applied to image analysis and prediction of the properties of functional materials. As an example, a new method is used to rapidly identify the crystallographic orientation parameters in multicrystalline silicon. The proposed method is based on machine learning technologies. The analysis of textured multicrystalline silicon wafers is carried out using the original single-crystal grain clustering algorithm, and the crystallographic orientation parameters are identified using a neural network model. The principle of identification is based on the correlation of the contrast of the macrostructure display associated with the reflective features of the grains and their orientation parameters. The architecture of the neural network - a multilayer perceptron - is chosen taking into account the restrictions on the number of input data. However, in conjunction with the algorithm, the optimal amount of training data satisfies the requirements of the neural network training process and ensures high efficiency in identifying orientation parameters on scanned images of textured multicrystalline silicon wafers.

The field dependence of the magnetization of a silicon nanosandwich, observed at room temperature, demonstrates a very complex character. The dependence is formed by the main contribution of the quantum magnetic effect, which is interpreted as the de Haas - Van Alphen effect with integer and fractional filling factors. Based on the previously found two-dimensional carrier density, the critical fields for the corresponding filling factors are calculated. Modeling of the de Haas - Van Alphen oscillations at a high temperature (T = 300 K) is performed according to a given distribution of the energy density of states of a silicon nanosandwich in the vicinity of Landau levels. The computational procedure is implemented on a supercomputer. The dependence of the carrier effective mass on the strength of the external magnetic field, previously discovered by us, is taken into account.

This work presents the Monte Carlo simulation results of gold droplet movement over a vicinal Si(111) surface during the gold deposition. The behavior of gold droplets on a singular silicon surface with (111) and (100) orientations is considered. It is found that the directional droplet motion on the vicinal Si(111) surface is caused by the asymmetry of lateral facets at the liquid-crystal interface. The asymmetry of lateral facets is caused by the presence of steps on the vicinal Si(111) surface. The reason for the gold droplet movement is the silicon substrate dissolution in the tendency to reach the Au-Si melt equilibrium concentration in the droplet bulk. The kinetics of Au-Si droplet movement on the silicon surface is analyzed.

One of the promising approaches to solving the problem of producing low-cost photodetector arrays is to develop diode arrays based on structures with PtSi/poly-Si Schottky barriers produced by standard CMOS processes. In creating such structures, several problems arise, and the present study is aimed at solving such problems. The diffusion of hydrogen atoms from a Si₃N₄ layer into a silicon film at room temperature at the step of formation of a Si/Si₃N₄ layer is detected and studied using Fourier-transform infrared spectroscopy. In studying the formation of PtSi/poly-Si layers, it is found that an interface film consisting of Pt₃Si and Pt₂Si silicides is formed on the surface of poly-Si during magnetron sputtering of platinum. When the Pt/(Pt₃Si+Pt₂Si)/poly-Si structure is heated to ∼ 300°C for 30 min, the transition of the Pt₃Si phase to the Pt₂Si phase occurs. A further increase in temperature leads to the formation of the PtSi compound; at the temperature of 480°C, all silicides completely transform into the PtSi phase.

The effect of coatings containing dysprosium or erbium ions on the properties of photosensitive structures based on porous silicon is investigated. The current-voltage, capacitance - voltage and spectral characteristics of structures with a p-n junction and films of erbium or dysprosium fluorides, as well as structures with an oxide layer of a complex composition containing erbium ions, are measured. The effect of X-ray radiation with a quantum energy of 6.9 keV on the photoelectric properties of structures with a porous layer and a coating of erbium fluoride is studied. A noticeable effect of the coating on the characteristics of the structures is shown.

The photoluminescence of float-zone silicon irradiated with high-energy xenon heavy ions (167 MeV) has been studied. In the photoluminescence spectra at low temperatures, in addition to the known X, W, W’, and C lines, a wide band appears in the region of 1.3 - 1.5 µm. With an increase in the irradiation dose in the range of 5·10¹⁰ - 10¹³ cm^-2, a decrease in the intensity and narrowing of the photoluminescence band is observed with a simultaneous shift of the maximum to the long-wavelength region. During subsequent annealing at temperatures of 400, 500, and 600 ^oC, changes in photoluminescence spectra are observed, associated with the transformation of the structure of defects in silicon. The temperature dependence of photoluminescence in the range from 10 to 170 K is studied for samples after irradiation with various doses and annealings.

The knowledge of the photoresist refractive index is useful for a number of applied tasks of controlling microelectronics technological processes, as well as for experimental studies of the characteristics of prototyped diffractive and micro-optical structures with deep microrelief. As this optical parameter depends on the photoresist treatment conditions, the spectral dependences provided at times by manufacturers may be insufficient. Research results of determining the refractive index dependence of positive photoresists S1818 G2 (MICROPOSIT) and FP-3535 (FRAST-M) in the wavelength range of 500-1600 nm on preliminary heat treatment conditions in the range of 15-30 min and exposure to actinic radiation are presented. The treatment of the investigated photoresists to obtain the refractive index within 1.61-1.64 in the visible spectral range and 1.59-1.61 in the near infrared spectral range of the emission spectrum is provided. An anomalous dispersion zone in the 570-640 nm wavelength range has been detected in films of the S1818 G2 dyed photoresist, which is often used in experimental characterization research in diffractive optical element prototyping. The dispersion curves for the Russian photoresist FP-3535 have been obtained for the first time.