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Resistivity, r (T), and Hall coefficient in weak (B < 1 T) magnetic fields, R (T), are investigated in Ca2Si and CaSi2 films at temperatures T between ~ 20 - 300 K. In CaSi2, r (T) is typical of metals increasing with T within the whole temperature range. On the other hand, the resistivity of Ca2Si is pertinent of semiconductors. Namely, it is activated below T ~ 200 K, exhibiting different slopes of ln r vs. T -1 plots at lower and higher T, and a weak increase between T ~ 200 - 300 K. Both materials demonstrate a complex dependence of R (T), including a change of the sign. Transport properties above have been analyzed assuming two groups of charge carriers, electrons and holes, contributing them.

The studies are devoted to the development of the technology of multilayer incorporation of nanocrystals (NCs) of semiconductor chromium and iron disilicides with a layer density no less than 2x1010 cm-2, the establishment of the growth mechanism of heterostructures with two types of NCs, the determination of their crystalline quality and optical properties, as well as the creation and study of rectification and photoelectric properties of p-i-n diodes based on them. Morphologically smooth heterostructures with 6 embedded layers of CrSi2 nanocrystals and two types of embedded nanocrystals (with 4 layers of CrSi2 NCs and 2 layers of β-FeSi2 NCs) for optical studies and built-in silicon p-i-n diodes were grown for the first time. The possibility of optical identification of interband transitions in embedded nanocrystals in the photon energy range of 1.2 - 2.5 eV was determined from the reflection spectra and the strongest peaks in reflection from the integrated nanocrystals were determined: 2.0 eV for CrSi2 NCs and 1.75 eV for β-FeSi2 NCs. The created p-i-n diodes have a contact potential difference of 0.95 V, regardless of the type of embedded NCs. At 80 K, an absorption band (0.7 - 1.1 eV) was detected in the diodes, which was associated with carrier photo generation in the embedded CrSi2 and β-FeSi2 NCs. From the spectra of the photoresponse at 80 K, the band gap widths in the NCs were determined: 0.50 eV in CrSi2 and 0.70 eV in the superposition of the CrSi2 and β-FeSi2 NCs.

The solid-state formation of gallium antimonide on Si(111) from a stoichiometric mixture of GaSb in the temperature range of 300 °C–500 °C and thicknesses of 12–40 nm was studied under ultrahigh vacuum conditions. The influence of the preformed GaSb seed islands on the morphology, composition, and structure was studied. It has been found that at 300 °C a strained continuous polycrystalline film is formed, which rupture at 350 °C. It has been shown that a continuous single-crystal GaSb film grows at 400 °C–500 °C if the sample is annealed at a weak antimony flow. This is also facilitated by the preliminary formation of a high density of nanosize GaSb seed islands. As a result, a continuous relaxed film with epitaxial relations GaSb(111)∣∣Si(111) and GaSb[1–10]∣∣Si[1–10] was obtained from a GaSb mixture 40 nm thick at 500 °C. We demonstrate a possibility of direct formation of GaSb on Si(111) without buffer layers of other chemical elements.

The morphology and structure of iron silicide nanorods formed on Si (111) vicinal surface by the SPE method at T = 630 °C were studied. Optimal Fe coverage and Fe deposition rate for the formation of a dense array of the nanorods (54-65% of the substrate area) on Si (111) surface with 3-4o miscut angles were established. The aspect ratio of the nanorods is 1.9 – 3.3. Cross-sectional images of a high-resolution transmission electron microscopy (HRTEM) have shown that the nanorods have α-FeSi2 crystal structure. They are strained along the “a” axis and stretched along the “c” axis, which increased the unit cell volume by 10.3%. According to HRTEM image analysis, the nanorods have the following epitaxial relationships: α-FeSi2[01]//Si [10] and α-FeSi2(112)//Si (111). All the data obtained have provided, for the first time, a direct evidence of α-FeSi2 nanorods formation on Si (111) vicinal surface without noticeable penetration of Fe atoms into the Si substrate.

The methods of heteroepitaxial growth of Si/CaSi2/Si(111) double heterostructures (DHS) at 500 °C have been developed. Thin CaSi2 layers with the thicknesses of 14–40 nm have been successfully embedded in the silicon matrix. The hR6-CaSi2(001)||Si(111) with hR6-CaSi2[100]||Si[1ī0] epitaxial relationship has been conserved for the embedded CaSi2 layer regardless of its thickness and the Si overgrowth mode (molecular beam epitaxy or solid phase epitaxy). The embedded CaSi2 layers are characterized by the lattice parameter distortion of about ±4% due to the difference in the thermal expansion coefficients of the silicide and silicon. Two types of Si overgrowth atop CaSi2(001) planes have been observed: (i) {111}-twinned Si crystals were found onto the CaSi2(001) surface in the DHS with CaSi2 thickness of 32–40 nm, which have preserved the {111} planes parallel to the Si(111) ones of the substrate; (ii) a polycrystalline twinned Si capping layer with a variable thickness has been formed in the samples with the smallest CaSi2 thickness (14–16 nm). Experimentally determined optical functions for the CaSi2 layer embedded in the silicon matrix have shown the presence of degenerate semiconducting properties with strong absorbance at the photon energies higher than 2.3 eV and small contribution from the free carrier absorption at 0.4–1.2 eV. Ab initio calculations within the generalized gradient approximation and screened hybrid functional of the hR-6 CaSi2 bulk with and without lattice distortion (by ±3%) have demonstrated the metal or gapless semiconductor energy band structure, because the Fermi level crosses several bands also assuming a huge free carrier concentration. The low-temperature Hall measurements and magnetoresistance measurements have proved that CaSi2 films on silicon are a gapless semiconductor with two types of carrier “pockets” (holes and electrons) that determine the resulting conductivity, concentration and mobility as a function of the Fermi level shift with the temperature increase. Mechanisms of the experimentally observed optical transparency of CaSi2 in the infra-red range are discussed.

The inhibitory effects of carrageenans (CRGs) on lipopolysaccharide (LPS) induced inflammation in a mouse model of endotoxemia and in complex therapy of patients with enteric infections of Salmonella etiology were studied. The atomic force microscopy (AFM) examination of LPS and its mixture with CRGs showed that the LPS morphology is significantly changed under the action of &kappa, and &kappa, /&beta, CRGs. CRGs were able to increase the synthesis of anti-inflammatory interleukin 10 (IL-10) in vitro, and, at low concentrations, their activity in the mixture with LPS was higher. The protective effect of CRGs against Escherichia coli LPS was studied in vivo by monitoring the biochemical and pathomorphological parameters. The &kappa, CRGs and food supplement &ldquo, Carrageenan-FE&rdquo, increased the nonspecific resistance of mice to E. coli LPS at the expense of the inhibition of processes of thymus involution, adrenals hypertrophy, thyroid atrophy, hypercorticoidism, glycogenolysis, and lactate acidosis. The estimation of the therapeutic action of food supplement Carrageenan-FE in complex therapy of patients with enteric infections of Salmonella etiology is given. Carrageenan-FE restores the system of hemostasis and corrects some biochemical indicators and parameters in the immune systems of patients. These results allow us to hope for the practical application of CRGs for lowering the endotoxemia level in patients under the development of the infectious process caused by Gram-negative bacteria.

The growth, structure, optical, electrical and thermoelectric properties of calcium silicides of various compositions on silicon substrates with (100) and (111) orientations were experimentally studied. It was found that when the atoms of Ca and Si are co-deposited on atomically clean silicon, the basis phases in the composition of the formed films depends on the substrate temperature and the annealing temperature: Ca2Si (TSi = 20°C, Tann = 330°C), CaSi (TSi = 190-320°C, Tann = 330°C) and CaSi2 (TSi = 500°C). It was established that the Ca2Si phase is a direct-gap semiconductor with a band gap of 0.82±0.02 eV, large contribution of defect levels to the absorption coefficient at energies 0.25 - 0.50 eV and huge transmission up 90% in the far IR region. In CaSi-based films the high transmission (30-40%) up to 25 μm was observed, which corresponds to a semimetal with a constant density of states near the Fermi level. It was found that CaSi-based films have the maximum Seebeck coefficient and the power factor (up to 430 μV/K and up to 1.14 × 10-6 W/(K2m), respectively) at 330K. CaSi2 films with CaSi2 lattice stretching and epitaxial ordering relative to the Si (100) substrate exhibit semimetal properties, with very high conductivity and light transparency (up 12%) in the photon energy range 0.06 - 0.65 eV.

Successively forming GaSb islands by solid-phase epitaxy and covering them with a silicon layer, a nanostructured material containing 4 layers of GaSb nanocrystals (NCs) was grown on Si (111) surface. Due to a small size of the NCs (average height ~ 1.7 nm, average lateral size ~ 14 nm) and, as a consequence, to a significant quantum-size effect, a high electrical conductivity (~ 100 Ω-1·cm-1at 600 K) together with a low thermal conductivity (~ 1 – 1.5 W·m-1·K-1at 600 K) was obtained in the nanostructured material Si/NC_GaSb/Si. As a result, the thermoelectric figure of merit of the material has reached 0.82 at 600 K.

Thin (200-600 nm) Si-Sn alloy films were grown under ultrahigh vacuum conditions by co-deposition of Si and Sn on the Si (100) substrate at room temperature. Investigations of the film structure by X-ray diffraction showed the preservation of the amorphous structure of Si-Sn films without the contribution of the Si1-xSnx alloy with sphalerite lattice at Sn concentration in the range of x=0.14-0.19. Analysis of optical spectra and calculations showed that an amorphous Si-Sn film with a Sn concentration of 19% is a semiconductor with indirect fundamental optical transition with very high absorption at photon energies 0.2 – 1.0 eV. It was found that precipitation of β-Sn occurs with an increase of Sn concentration up to 40%, which is accompanied by an increase in the reflection coefficient to 0.6-0.8 at photon energies below 0.8 eV. The limited temperature stability of amorphous Si-Sn films is shown for high-energy and long-term (10 minutes) laser irradiation due to the formation of metallic precipitates of β-Sn.

A double-layer heterostructure with embedded into single-crystal silicon matrix nanocrystals (NCs) of gallium antimonide (GaSb) was grown. The NCs were formed by solid phase epitaxy method using 1.6-nm-thick Ga-Sb stoichiometric mixture and annealing at a temperature range of 200–500 °C. The embedded NCs have a concentration of about 5.4 × 1010 cm− 2, a mean height of 8.6 nm and a mean lateral dimension of 19.2 nm. A stress induced inside the NCs owing to lattice mismatch between Si and GaSb was fully relaxed by edge dislocations at Si/GaSb interface. All the NCs have identical epitaxial relationship: GaSb(111)||Si(111), GaSb 1 1 − 0 ||Si 1 1 − 0 .

The formation of iron silicide nanocrystals (NCs) and their embedding into monocrystalline silicon was studied. Solid phase epitaxy of 0.4 nm Fe at 630 °C resulted in formation of NCs consisted of β-FeSi2 and e-FeSi phases. Annealing of NCs at 750 °C for 90 min led to transformation of β-FeSi2 and e-FeSi into α-FeSi2. On the other hand, silicon layer growth over as-formed NCs, at the same temperature, resulted in formation of single phase NCs consisted of β-FeSi2. Silicon deposition rate proved to be the crucial point for a full embedding of NCs. The rate of 1 nm/min resulted in emersion of NCs to the surface during silicon overgrowth irrespective of Si cap layer thickness, while the rate of 8 nm/min led to the full embedding of β-FeSi2 NCs. Both incompletely and fully embedded β-FeSi2 NCs have epitaxial relationship and stress favorable for an indirect to direct band-gap transition at Y point.

Thin Mg2Ge films were grown using two methods: a co-deposition of Ge and Mg on Si substrate kept at room temperature followed by annealing at 200 °C (solid phase epitaxy – SPE) and reactive deposition epitaxy (RDE) of Ge and Mg on Si at 200 °C. Optical properties of these structures were investigated in the photon energy range of 0.02–6.2 eV. Based on optical functions calculation, it was shown that SPE growth results in formation of a crystalline layer of Mg2Si, which exhibits a strong optical phonon originated from the substrate-film interface. In the case of RDE growth, the amount of Mg2Si is sufficiently lower, but Mg‑Si-Ge compound phonon appears. The estimate of a fundamental indirect transition value in the film is 0.72 eV for SPE growth method and 0.56 eV for RDE due to the ternary compound Mg-Ge-Si at the film-substrate interface.

An array of GaSb nanocrystallites (NCs) was formed on Si(001) substrate by solid-phase epitaxy at 500 °C. Owing to the embedded GaSb NCs, p+‑Si/NC‑GaSb/n‑Si mesa diode spectral sensitivity has extended up to 1.6 µm at room temperature, and its integral sensitivity has increased by 4–5% in the wavelength range of 1200–1600 nm, as compared to a conventional Si diode. This result was achieved by embedding only 10 nm of GaSb in the form of NCs inside a silicon matrix. In addition, we could obtain a significant electroluminescence (EL) signal at 120 K in a very wide wavelength range from 1.3 to 2.1 µm (0.95–0.59 eV). The EL spectrum has a broad maximum at 1700 nm (0.73 eV). The threshold pumping current density was as low as 0.75 A/cm2.

This article investigates the growth of calcium (Ca) silicides on the Si(001)2x1 surface during molecular beam epitaxy (MBE) from two sources of Ca and Si with a variable flow ratio from three to 10 at a fixed substrate temperature of 500 °C. According to atomic force microscopy (AFM), the grown films consist of grains with a mutually perpendicular orientation and have pronounced grain boundaries with an inhomogeneous relief. The best crystalline qualities of the films, both CaSi and CaSi2, were confirmed for the minimum ratio (about 3.0) of Ca to Si deposition flows by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) data in both cross-sections and in planar sections. At the same time, according to XRD and HRTEM data, for all formed films over the CaSi(010) layer on Si(001), the growth of hR3-CaSi2 was observed with epitaxial relationships: hR3-CaSi2(001)//CaSi(010)//Si(001). An analysis of these studies showed that calcium monosilicide (CaSi) is the first silicide phase in the Ca–Si(001) system at 500 °C due to (1) the maximum modulus of its heat of formation, (2) a decrease in the Ca accommodation coefficient to silicon less than unity and the formation of a mixture close to CaSi, (3) a better matching between the parameters of the CaSi(010) plane lattice and the Si(001) plane lattice, and (4) lower CaSi (010)/Si (001) interface energy compared with the CaSi2(001)/Si(001) system. It is assumed that the formation of CaSi2 occurs in the subsurface region of the growing film at 500 °C due to increased diffusion of Ca atoms into the Si substrate and increased intergranular diffusion of Si atoms, which leads to the formation of a mixture with the CaSi2 composition. Both factors create conditions for the crystallization of CaSi2 on the surface of the CaSi layer at Т = 500 оС. The epitaxial ordering of CaSi2 on the CaSi surface and the decrease in the energy of hR3-CaSi2(001)/CaSi(010) interface is associated with small distortions of their lattices during superstructural matching, which is proved by modeling their matching.

The study of the optical properties of BaSi2 films grown on n-type silicon by solid-phase epitaxy showed that the band gap of BaSi2 is about 1.20 eV. Formed Al/BaSi2/Si mesa-diodes showed the presence of two maxima in the photoresponse spectra at 1.15–1.20 eV and 1.5–1.6 eV at 300K and spectra expansion to 0.7 eV at 80 K. Analysis of the I-V characteristics and photoresponse spectra at two biases showed that a BaSi2-n/Si-n isotype heterojunction is formed with a double barrier layer, quasi-linear I-V characteristics, and contribution of defect states to the photoresponse at 80 K. Band diagrams of the BaSi2-n/Si-n heterojunction with surface states at zero, forward and reverse biases were constructed, which made it possible to explain features in the photoresponse spectra at energies of 1.0-2.1 eV and the first detected IR photoresponse at 0.7-1.0 eV based on charging and photogeneration of defect states at 80K.

Nanocrystalline GaSb films were grown on Si(001) from the stoichiometric Ga&ndash, Sb mixture using solid-phase epitaxy at temperatures of 200&ndash, 500 &deg, C. Use of the solid-phase epitaxy method allowed the suppression of Ga surface diffusion and prevention of intense Sb desorption. At the annealing temperature of 300 &deg, C, a 14-nm-thick GaSb film aggregates, while a 20-nm-thick GaSb film remains continuous with a roughness of 1.74 nm. A GaSb film with a thickness of 20 nm consists of crystalline grains with a size of 9&ndash, 16 nm. They were compressed by ~2%. For some GaSb grains, new epitaxial relationships have been found: GaSb ( 111 ) ||Si ( 11 1 &macr, ) and GaSb [ 11 2 &macr, ] ||Si [ 1 1 &macr, 0 ] , GaSb ( 113 ) ||Si ( 11 1 &macr, ) and GaSb [ 1 1 &macr, 0 ] ||Si [ 1 1 &macr, 0 ] , and GaSb ( 11 1 &macr, ) ||Si ( 002 ) and GaSb [ 1 1 &macr, 0 ] .

Formation of GaSb by means of solid phase epitaxy of amorphous Ga:Sb (1:1) layer on Si (001) substrate at 500 °C has been studied. At amorphous layer thickness of 16 nm, a continuous nanocrystalline layer of GaSb was formed. Decreasing of amorphous layer thickness up to 0.8 nm resulted in formation of separated GaSb nanocrystallites (NCs), which had a mean lateral size of 30–80 nm and mean height of 2–3 nm, while their concentration reached 3×109 cm-2. Atomic force microscopy and low energy electron diffraction data showed that GaSb NCs could be fully embedded into silicon lattice by deposition of 25-nm-thick silicon layer at 650 °C. Nevertheless, on a surface of the silicon layer, some holes have been formed because of NCs moving toward to the surface. The holes formation can be almost completely suppressed by deposition of additional 25-nm-thick silicon layer at 500 °C – so-called “stop-layer”.

BaSi2 thin films were formed on Si (111) substrate by solid-phase epitaxy (SPE) (UHV deposition) using the template technology followed by vacuum annealing at temperatures of 600 °C and 750 °C. After the deposition and annealing barium silicide films were characterized by Auger electron spectroscopy, grazing incidence x-ray diffraction (GIXRD) and atomic-force microscopy (AFM). It was established that the films annealed at T = 600 °C are polycrystalline with the structure of the orthorhombic BaSi2, with grain sizes of 100-200 nm. Higher anneal temperature (T=750 °C) leads to increase of diffraction peak intensity of BaSi2 phase with grain coagulation into 300-400 nm islands. It was confirmed that nanocrystalline BaSi2 films are characterized by a direct fundamental interband transition at 1.3 eV, the second interband transition with an energy of 2.0 eV, own phonon structure with wave number peaks at 112, 119, 146 and 208 cm-1 and a high density of defect states within the band gap, which provide a noticeable subband absorption at energies of 0.8 – 1.1 eV.

Three-layer heterostructures with embedded CrSi2 nanocrystallites were grown using molecular-beam epitaxy. The nanocrystallites have epitaxial orientation to the silicon lattice and are subjected to anisotropic compressive stress in the CrSi2 [001] direction. The thermoelectric power factor of the heterostructure is about 5 times higher than that in the substrate at 300–480 K. Taking into consideration the ratio of nanocomposite and substrate thickness, the real power factor is expected to be 2–3 orders higher than the measured one and it reaches 3200 μW K-2 m-1 at 470 K. Open image in new window

The electroluminescence efficiency of silicon light-emitting diode structures with several layers of β-FeSi2 nanocrystallites embedded in the p-n junction is investigated. The nanocrystallites were formed by either solid-phase epitaxy or a combination of reactive and solid-phase epitaxy. For the structures in which the nanocrystallites were formed by the combined method, electroluminescence is observed only at low temperatures (below 70K). This is indicative of a high concentration of defects acting as nonradiative-recombination centers. For the structures with nanocrystallites formed by solid-phase epitaxy, intense electroluminescence is observed up to room temperature. The dependence of the electroluminescence intensity on the size of the nanocrystallites is studied.

Currently, scanning probe microscopy (SPM) is actively used to obtain surface data. A large number of images require a fast and high-accuracy calculation of the topographic parameters of particles on the surface. The original grain analysis algorithm based on finding a local maximum is realized by sorting an array of points forming the topography of the SPM image surface. It provides to determine various topographic characteristics of objects located on a surface (height, lateral dimensions, area, volume, etc.)

Embedded in silicon β-FeSi2 nanocrystals (NCs) were grown on Si(111) by solid phase epitaxy of a thin iron film followed by Si molecular beam epitaxy. After solid phase epitaxy, a mixture of β-FeSi2 and e-FeSi nanocrystals is formed on the surface, sometimes β and e phases coexist inside one nanocrystal. During initial stage of Si molecular beam epitaxy all e-FeSi transforms into β-FeSi2. β-FeSi2 nanocrystals tend to move following Si growth front. By adjusting growth condition, we manage to prevent the nanocrystals from moving and to fabricate 7-layer n-Si(111)/β-FeSi2_NCs/p+-Si silicon heterostructure with embedded β-FeSi2 NCs. An epitaxial relationship and a stress induced in the nanocrystals by silicon matrix were found to be suitable for indirect to direct band gap transition in β-FeSi2. Of the heterostructure, a n-i-p avalanche photodetector and a light-emitting diode were formed. They have shown relatively good performance: ultrabroadband photoresponse from the visible (400 nm) to short-wavelength ...

By method of in situ differential spectroscopy it was established that at the formation of monolayer Fe, Cr, Ca, Mg silicide and Mg stannide islands on the atomically clean silicon surface an appearance of loss peaks characteristic for these materials in the energy range of 1.1-2.6 eV is observed. An optimization of growth processes permit to grow monolithic double nanoheterostructures (DNHS) with embedded Fe, Cr and Ca nanocrystals, and also polycrystalline DNHS with NC of Mg silicide and Mg stannide and Ca disilicide. By methods of optical spectroscopy and Raman spectroscopy it was shown that embedded NC form intensive peaks in the reflectance spectra at energies up to 2.5 eV and Raman peaks. In DNS with β-FeSi2 NC a photoluminescence and electroluminescence at room temperature were firstly observed.

A conductivity quasi-two-dimensional system formed by nanocrystallites CrSi2 located in the crystallographic (111) plane of silicon has been considered. At low temperatures the system exhibits several unique properties: (i) the activation energy in the temperature dependence of resistance is appreciably lower than in the case of impurity condition; (ii) the carrier mobility is very high but it decreases rapidly with the growing temperature; (iii) the magnetoresistance is linear and decreases rapidly as the temperature rises. To explain these features, a model has been proposed which assigns special importance to the charges at the nanocrystallites which appear due to the escape of the electrons to the conduction band (or holes to the valence band) of silicon.

The [Formula: see text]–[Formula: see text]–[Formula: see text] diode structures with a variable number of [Formula: see text]-FeSi2 and CrSi2 nanocrystal (NC) bilayer were studied at room and liquid nitrogen temperatures. The high crystal quality of Si and embedded NCs was determined by HRTEM cross-sectional data. This diode demonstrated a photoresponse in the IR region (1.02–0.8[Formula: see text]eV) which was associated with a decrease in recombination losses with the main contribution coming from CrSi2 NCs. Calculations of photoyield and its extrapolation to zero resulted in band gap values of 0.35[Formula: see text]eV at 300[Formula: see text]K and 0.46[Formula: see text]eV at 90[Formula: see text]K. The spectral sensitivity of [Formula: see text][Formula: see text]A/W and specific detectivity of [Formula: see text][Formula: see text](cm Hz[Formula: see text]/W) were determined at [Formula: see text][Formula: see text][Formula: see text]m and T=300[Formula: see text]K.

Light-emitting silicon diode structures with embedded β -FeSi2 nanocrystallites have been fabricated using solid phase epitaxy and a combination of reactive deposition and solid phase epitaxy. Electroluminescence (EL) of the structures is studied over various temperatures and current densities under forward and reverse biases. We can state that β -FeSi2 NCs formed by the combined RDE+SPE method results in the formation of high density of dislocations and point defects. In contrast, defect-free structures with β -FeSi2 NCs formed by SPE demonstrate intense EL (η = 1.2×10-5%) in the wavelength range 1.4–1.6 µm even at room temperature. EL intensity dependence on the number of layers with embedded β -FeSi2 NCs is almost linear for the heterostructures formed on Si(100) and sublinear for the heterostructures formed on Si(111) substrate. The increase of the initial Fe layer thickness leads to the electroluminescence quenching. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The behaviors of resistance, magnetoresistance (up to 5 T), and Hall electromotive force (EMF) with varying temperature (10–300 K) and measuring current (A–10 mA) are studied for the Si sample with CrSi2 nanocrystallites (NC) in the plane (111). The conduction in such heterostructure proceeds in the plane with the NC and is the conduction of a two-dimensional system of charge carriers that shows some unusual effects. The temperature variation of resistivity may be treated as the result of the effect of thermal activation but in this case it is characterized by a low activation energy different in value in different temperature ranges. This suggests that the mechanism of conduction is more complex. It is found that the conduction is determined by the effect of temperature variation not only on carrier concentration but also on its mobility. Magnetoresistivity is also of different shape in different temperature ranges. All the above features are treated in terms of the proposed model of electron hopping through the conduction band (or hole hopping through the valence band). A peculiar effect of giant reduction in resistivity with increasing the measuring current has been revealed. Discussed are some possible factors responsible for this effect.

The electronic structure and morphology of calcium silicide films formed by reactive deposition epitaxy at 130 oC on Mg2Si film and at 500 oC on Si(111)7x7 surface, their optical and electrical properties have been investigated. Formation of new calcium silicide phase with high Si concentration, indirect band gap (0.63 eV), high conductivity at low temperatures (50-450 K) has been obtained after calcium deposition at 500 oC on Si(111)7x7 surface.

The LEED patterns, electronic structure and morphology of Si(5 5 12) substrate surface were studied after different temperature cleaning procedures: high temperature (1250 oC), low temperature (900 oC) and cleaning at 800 oC in low silicon atom flow. The low temperature annealing without using of Si flow has been determined as the optimal cleaning procedure for Si(5 512) substrate.

In this work buried nanocrystalline CrSi2 layers were synthesized by ion implantation, pulsed annealing and MBE. The structural, optical and thermoelectrical properties of CrSi2 layers were studied by methods of SEM, TEM, RBS, PL and Seebeck coefficient measurements. The characteristic features of pulsed nanosecond annealing of Cr-implanted Si and epitaxial growth of triple Si/nc–CrSi2/Si heterostructures were established. It is shown that grown Si/nc–CrSi2/Si heterostructures, which preliminary implanted with the high-dose ( ϕ = 6 × 1016 cm − 2 ) of Cr+ ions, have the noticeable low temperature ( T = 10 – 100 K ) photoluminescence signal at 1450–1600 nm and the large Seebeck coefficient (−(60–300) μV/K) in the temperature range of T = 340 – 415 K .

Using electron energy loss spectroscopy, Raman spectroscopy, and conductance measurements in the temperature range 20–500 K we have investigated doping of two-dimensional Mg silicide using the Sb surface phase. The doping process was performed in two steps including formation of the Sb surface phase followed by reactive deposition of Mg. It was shown that additional levels appear in the Mg 2 Si band gap resulting in increasing conductance at high temperatures. The Sb doped Mg 2 Si layer has a band gap of about 1.2 eV.

The effect of pulsed ion-beam annealing on the surface morphology, structure, and composition of single-crystal Si(111) wafers implanted by chromium ions with a dose varying from 6 × 1015 to 6 × 1016 cm−2 and on subsequent growth of silicon is investigated for the first time. It is found that pulsed ion-beam annealing causes chromium atom redistribution in the surface layer of the silicon and precipitation of the polycrystalline chromium disilicide (CrSi2) phase. It is shown that the ultrahigh-vacuum cleaning of the silicon wafers at 850°C upon implantation and pulsed ion-beam annealing provides an atomically clean surface with a developed relief. The growth of silicon by molecular beam epitaxy generates oriented 3D silicon islands, which coalesce at a layer thickness of 100 nm and an implantation dose of 1016 cm−2. At higher implantation doses, the silicon layer grows polycrystalline. As follows from Raman scattering data and optical reflectance spectroscopy data, semiconducting CrSi2 precipitates arise inside the silicon substrate, which diffuse toward its surface during growth.

We develop an approach and present results of the combined molecular dynamics and density functional theory calculations of the structural and optical properties of the nanometer-sized crystallites embedded in a bulk crystalline matrix. The method is designed and implemented for both compatible and incompatible lattices of the nanocrystallite (NC) and the host matrix, when determining the NC optimal orientation relative to the matrix constitutes a challenging problem. We suggest and substantiate an expression for the cost function of the search algorithm, which is the energy per supercell generalized for varying number of atoms in the latter. The epitaxial relationships at the Si/NC interfaces and the optical properties are obtained and found to be in a reasonable agreement with experimental data. Dielectric functions show significant sensitivity to the NC's orientation relative to the matrix at energies below 0.5 eV.

It is demonstrated by the Surface Magneto-Optic Kerr Effect and Differential Reflectance Spectroscopy methods that structures free of magnetically dead layers can be created by the deposition of iron at room temperature onto a prefabricated magnetic silicide layer. The magnetic silicide can be formed by the deposition of iron at 70 ∘C onto a layer of amorphous silicon prefabricated on Si(100). Both in the silicide and the iron film, magnetism onsets after the iron amount deposited reaches some critical value. The spontaneous magnetization vector in the iron film changes its direction twice during the film growth. Sufficiently thick iron films persist being ferromagnetic in air for years.

Growth and the optical properties of epitaxial heterostructures Si(111)/(CrSi2 nanocrystallites)/Si(111) based on nanosized islands of chromium disilicide (CrSi2) on Si(111) were studied using low-energy electron diffraction, atomic-force microscopy, and optical reflection and transmission spectroscopy. The heterostructures with thicknesses of 0.1, 0.3, 0.6, 1.0, and 1.5 nm were formed by reactive epitaxy at a temperature of 500°C followed by the epitaxial growth of silicon at 750°C. The specific features of changes in the density and sizes of CrSi2 islands on the silicon surface were determined at T = 750°C as the chromium layer thickness was increased. It was established that, in the heterostructures with chromium layer thicknesses exceeding 0.6 nm, a small part of faceted Cr2Si2 nanocrystallites (NCs) emerge into near-surface region of the silicon, which is confirmed by the data from optical reflectance spectroscopy and an analysis of the spectral dependence of the absorption coefficient. A critical size of NCs is shown to exist above which their shift to the silicon surface is hampered. The decreased density of emerging NCs at chromium layer thicknesses of 1.0–1.5 nm is associated with the formation of coarser NCs within a silicon layer, which is confirmed by the data from differential reflection spectroscopy.

The growth of nanosize islands of iron silicides on Si(100) substrates and epitaxial silicon over-growth atop them have been studied by low energy electron diffraction and reflectance high energy electron diffraction methods. The near optimal formation conditions of iron silicide islands with high density and minimal sizes have been determined by using of atomic force microscopy. Multilayer (8–10) monolithic structures with buried iron silicide nanocrystallites have been grown after the definition of monocrystalline burying conditions of iron silicides nanocrystallites in silicon lattice. The structure of buried nanocrystallites has been studied in multilayer monolithic heterostructures by high resolution transmission electron microscopy. It was established that in multilayer samples the majority of nanocrystallites have β-FeSi2 structure, but some of them have γ-FeSi2 structure. It was observed an influence of additional annealing at 850 °C on the morphology and structure of nanocrystallites. By means of deep level transient spectroscopy data one and two trap levels have been observed in multilayer structures (without and with additional annealing, respectively). Photoluminescence spectra have been studied at 4.2 K and the causes of its absence from buried β-FeSi2 NC have been analyzed.

The method of ultrahigh-vacuum low-temperature (T = 850°C) purification of silicon single crystals having the (100) and (111) orientation and implanted with low-energy (E = 40 keV) iron ions with various doses (Φ = 1015−1.8×1017 cm−2) and subjected to pulsed ion treatment (PIT) in a silicon atom flow has been tested successfully. The formation of semiconducting iron disilicide (β-FeSi2) near the surface after PIT is confirmed for a Si(100) sample implanted with the highest dose of iron ions. The possibility of obtaining atomically smooth and reconstructed silicon surfaces is demonstrated. Smooth epitaxial silicon films with a roughness on the order of 1 nm and a thickness of up to 1.7 μm are grown on samples with an implantation dose of up to 1016 cm−2. Optical properties of the samples before and after the growth of silicon layers are studied; the results indicate high quality of the grown layers and the absence of iron disilicide on their surface.

Methods of low-energy electron diffraction, measurements of the Hall effect in situ, atomic-force microscopy, and high-resolution transmission electron microscopy were used to study the formation of iron silicide islands on the Si(100)–(2×1) surface and overgrowth of these islands with silicon; the electrical properties and structure of silicon with buried iron silicide nanocrystallites were studied. The best crystal quality of the continuous single-crystal silicon layer and the minimum roughness of its surface were observed at the silicon growth temperature of 700°C and the layer thickness of 100 nm. A model of growth of silicon over the ironsilicide nanocrystals is suggested. Two types of formed nanocrysrallites were found: small nanocrystallites (5–6 nm) of β-FeSi2 and large nanocrystallites (30–50 nm) of γ-FeSi2. The good agreement between the electrical parameters of silicon with buried iron disilicide nanocrystallites and those of atomic-clean silicon confirmed that there is minimum scattering of charge carriers at nanocrystallites in the temperature range of 300–540 K.

The morphology and optical properties of Si samples implanted by low-energy Fe+ ions with different fluences (1 × 1015–1.8 × 1017 cm−2) and further subjected to pulsed ion-beam treatment (PIBT) have been studied by atomic force microscopy and optical reflectance spectroscopy. It was proved that iron disilicide (β-FeSi2) crystallites were formed on the surface of the Si substrate as a result of ion implantation and PIBT. The method of ultrahigh vacuum and low-temperature (T = 850 °C) cleaning of Fe+-implanted Si samples has been applied for the first time. It was found that it is possible to form smooth epitaxial Si films with both a thickness of up to 1.7 µm and a reconstructed surface by molecular beam epitaxy on the surface of Si samples implanted with a fluence of up to 1 × 1016 cm−2. Further increase in the implantation fluence results in the disruption of epitaxial Si growth and to a strong increase in surface relief roughness due to 3D silicon growth mechanism. Preservation of β-FeSi2 precipitates inside the Si matrix after the formation of a cap epitaxial Si layer has been confirmed by optical spectroscopy data. Low temperature photoluminescence measurements in the range 1400–1700 nm showed that light emission of the formed Si/β-FeSi2/Si heterostructures is due to contributions from β-FeSi2 precipitates and dislocations.

Low-energy electron diffraction and differential reflectance spectroscopy are used to study the self-formation of chromium disilicide (CrSi2) nanoislands on a Si(111) surface. The semiconductor properties of the islands show up even early in chromium deposition at a substrate temperature of 500°C, and the two-dimensional growth changes to the three-dimensional one when the thickness of the chromium layer exceeds 0.06 nm. The maximal density of the islands and their sizes are determined. The MBE growth of silicon over the CrSi2 nanoislands is investigated, an optimal growth temperature is determined, and 50-nm-thick atomically smooth silicon films are obtained. Ultraviolet photoelectron spectroscopy combined with the ion etching of the specimens with embedded nanocrystallites demonstrates the formation of the valence band, indicating the crystalline structure of the CrSi2. Multilayer epitaxial structures with embedded CrSi2 nanocrystallites are grown.

Iron silicide island growth on Si(100)2 × 1 surface, silicon growth over iron silicide nanosize islands and structure of silicon and buried iron silicide nanocrystallites have been studied by low electron energy diffraction, atomic force microscopy and high resolution transmission electron microscopy. The best crystal quality of the continuous monocrystal silicon layer and minimal roughness have been observed for the silicon growth temperature T = 700 °C and silicon layer thickness 100 nm. Nanocrystallites of two types have been observed: small (5–6 nm) and large (30–50 nm). A model of silicon growth atop Si(100) substrate with nanosize iron silicide islands at different substrate temperatures has been proposed. The crystal structure and sizes have been determined for β-FeSi2 and γ-FeSi2 nanocrystallites.

By using solid phase epitaxy of thin Fe films and molecular beam epitaxy of Si, a p+-Si/p-Si/β-FeSi2 nanocrystallites/n-Si(111) diode structure was fabricated. Transmission electron microscopy data confirmed a well-defined multilayered structure with embedded nanocrystallites of two typical sizes: 3–4 and 15–20 nm and almost coherent epitaxy of the nanocrystallites with the Si matrix. The diode at zero bias conditions exhibited a current responsivity of 1.7 mA/W, an external quantum efficiency of about 0.2% and a specific detectivity of 1.2 × 109 cm × Hz1/2/W at a wavelength of 1300 nm at room temperature. In the avalanche mode, the responsivity reached up to 20 mA/W (2% in terms of efficiency) with a value of avalanche gain equal to 5. The data obtained indicate that embedding of β-FeSi2 nanocrystallites into the depletion region of the Si p-n junction results in expansion of the spectral sensitivity up to 1600 nm and an increase of the photoresponse by more than two orders of magnitude in comparison with a conventional Si p-n junction. Thereby, fabricated structure combines advantage of the silicon photodiode functionality and simplicity with near infrared light detection capability of β-FeSi2.