Home – Home – Jornals – Avtometriya 2014 number 3

A kinetic diagram of Ge growth on Si is constructed by methods of fast electron diffraction and scanning electron microscopy. Activation energies of morphological transitions from twodimensional to three-dimensional growth and from hut-clusters to dome-type islands are determined. The curve of the 2D -3D transition has two segments that follow the Arrhenius law and refer to different mechanisms of two-dimensional growth: two-dimensional island mechanism in the temperature range of 300-525 ºC with the activation energy of −0.11 eV and step motion in the temperature range of 525-700 ºC with the activation energy of 0.15 eV. Transitions from hut-islands to dome-islands are also observed. The curve constructed for the hut-dome transition is approximated by two exponential segments that obey the Arrhenius law. The hut-dome transition activation energy is 0.11 eV in the temperature range of 350-550 ºC and 0.24 eV in the temperature range of 550-700 ºC. The maximum density of islands in the case of Ge growth on a Ge_x Si_{1 − x} layer reaches 4 · 10¹¹ cm⁻². An increase in the composition leads to an increase in the density of Ge islands owing to a decrease in the length of migration of Ge adatoms on the Ge_xSi_{1 − x} surface, as compared to the case of Ge growth on Si. The periodicity N, which is manifested as a (2 × N ) superstructure, decreases during the reconstruction from 14 to 8 with increasing Ge content in the Ge_xSi_{1 −x} layer. An increase in thickness or temperature leads to a decrease in periodicity and testifies to Ge segregation; in this case, stress relaxation occurs, which reduces the Ge diffisivity.

GaAs films on Si substrates miscut from the (001) plane by 6º in the [110] direction are grown by molecular beam epitaxy (MBE). GaAs films are grown both on the Si surface terminated by arsenic atoms and on thin pseudomorphic GaP/Si layers. The condition of formation of the As sublayer and the first monolayer of GaP on the Si surface is defined as the GaAs film orientation (001) or (00¯1). The processes of Si surface preparation and formation of the As sublayer and GaAs and GaP epitaxial layers are monitored by means of high-energy electron diffraction reflection (RHEED). The grown structures are investigated by methods of X-ray diffraction, atomic force microscopy (ATM), high-resolution transmission electron microscopy (HRTEM), and low-temperature luminescences. It is shown that the epitaxial film orientation affects both the surface morphology and its crystalline properties. Intense photoluminescence is obtained from the In_0.17Ga_0.83As quantum well structure grown on the GaAs/Si buffer layer.

Initial stages of ZnTe growth on GaAs(301) and Si(301) substrates by the method of molecular beam epitaxy are investigated by means of in situ one-wave ellipsometry. Layer-by-layer growth of the ZnTe film is observed on GaAs(301) substrates, whereas 3 D nucleation occurs during epitaxy on Si(301) substrates. Misfit dislocations (MDs) are inserted into the ZnTe film during the growth of the first monolayers. Owing to MDs, the film lattice turns with respect to the substrate lattice, which is confirmed by X-ray measurements. Threading segments of MDs in CdTe/ZnTe/GaAs(301) and CdTe/ZnTe/Si(301) heterostructures are subjected to etching. The etch dislocation pits are found to have different shapes, which testifies to different types of threading dislocations. In the case of layer-by-layer etching, the dislocation density is found to increase inward the CdTe film, which testifies to annihilation of dislocations in the course of growth of CdTe films. The dislocation annihilation rate is higher in films grown on GaAs(301) than in those grown on Si(301). A possible reason is the higher mobility of dislocations in CdTe films on GaAs(301) substrates.

The structure of extended defects introduced into Si by means of boron implantation followed by thermal annealing at T = 900 ºC is studied by the method of high-resolution transmission electron microscopy and computer modeling for different values of the implantation dosage (D) and concentration of boron atoms in substitutional positions B₀(C_B0) injected into the Si lattice before implantation. It is shown that the Frank dislocation loops of both interstitial (I) and vacancy (V) type at a ratio of 4 : 1 are observed in Si samples with D = 10¹⁶ cm⁻² up to C_B0 = 0.8 · 10²⁰ cm⁻³. The atomic structure of the I-type Frank dislocation loops is heavily deformed, which suggests segregation of finely dispersed boron in the defect plane. At the same time, the structure of the V-type Frank dislocation loops tends to be reconstructed due to interaction with self-interstitials. At C _B0 = 2.5 · 10²⁰ cm⁻³, the I-type Frank dislocation loops are found to transform to perfect dislocation loops, and boron precipitates with a high density appear in Si. Based on the results obtained, probable reasons for vacancy deficit formation in boron-implanted Si are discussed.

The molecular dynamics method is used to study the formation of Ge nanoislands on pit-patterned Si(100) substrates. For substrates with overlapping pits and pits in the shape of truncated inverted pyramids, the energy surface is calculated. On the basis of its analysis, the mechanism of nuclear surface diffusion on the pit-patterned surface is described. The specific energy of Ge/Si heterostructures with different morphology of nanoislands in pits is calculated. It is shown that the configuration with multiple nanoislands in a pit can be thermodynamically favorable.

Results of mathematical simulation of the hole spectrum and optical absorption in Si/Ge_xSi_{1 − x}/Si quantum wells formed on virtual Ge_ySi_{1 − y} substrates are presented. It is shown that the presence of elastic strains in such a system can significantly change the position of absorption lines in GeSi heterostructures. Selecting the quantum well and virtual substrate compositions can change the intersublevel absorption wavelength in the range from 6 to 12 µm for light polarized in the quantum well plane. When tensile strain is applied, the change in the hole transition intensity under the influence of the light polarized in the quantum well plane reaches a factor of 1.8. Compressive strain changes the intersubband transition intensity by a factor of 1.45.

Tools for optimizing the performance of parallel programs on multi-architectural distributed computing systems are considered. A method for optimizing the embedding of parallel MPIprogram into computing clusters with a hierarchical communication network structure is described. An adaptive approach to the delta optimization of restore points is proposed for effective fault-tolerant simulation on distributed computing systems.

The results of investigation of photostimulated current switching during irradiation of mesoscopic structures based on Ge quantum dots in Si by weak infrared fluxes are presented. The small dimensions of the channel (approximately 70-200 nm) provide an opportunity to observe giant photoconductivity fluctuations which are due to the strong dependence of the hopping current on the filling of quantum dots by charge carriers. Replacing the silicon substrate with silicon-on-insulator made it possible to exclude the predominance of band conduction over hopping conduction at high temperatures and increase the photodetection temperature from 4.2 to approximately 100 K. The obtained results are the basis for the creation of a single-photon detector in a wide wavelength range.

The Raman scattering spectroscopy method is used to study the interaction of phonons and free charge carriers in doped semiconductor nanostructures (superlattices). In doped superlattices based on polar semiconductors, the collective vibrational modes of free charge carriers (plasmons) shield the long-range Coulomb interaction of cations and anions, which leads to the formation of mixed phononplasmon modes. The angular dispersion (anisotropy) of phonon-plasmon modes in doped GaAs/AlAs superlattices is studied. The observed anisotropy is due to the anisotropy of dielectric permeability in superlattices.

The dependence of the microwave insertion loss on the parameters of the heterostructure pin–diode is investigated by means of numerical modeling. The mechanisms of the emergence of this loss are determined, and the most influential mechanism is identified.

Spectral characteristics of metamaterials made of arrays of novel cylindrical resonators coupled with a substrate are simulated. It is shown that, apart from the usual modes, these resonators support additional modes due to a special shape of the resonators and to the presence of a dielectric substrate. In addition to the main resonance, the spectral characteristic has a resonance peak depending on the width of the transverse slit of the cylinder and the dielectric permittivity of the substrate. The dependences obtained in this work can be used to develop novel dynamically controlled metamaterials.

The evolution of the energy position of the maximum of the free exciton photoluminescence line in high-quality GaAs/AlGaAs heterostructures under optical excitation by short laser pulses of high density 5 · 10¹⁴–2 · 10¹⁸ cm⁻³ is considered. The influence of screening of the Coulomb interaction and interexciton exchange interaction are discussed. These effects give corrections to the exciton peak energy position of opposite signs. The second effect is sensitive to the exciton spin orientation and is manifested as splitting of the energy peaks of excitons with angular momentum projections +1 and −1. The value of splitting is proportional to the density of excitons and to the degree of their spin polarization and reaches 1.5 meV.

This paper presents a study of the effect of swift heavy Xe ions of energy 130-167 MeV at doses of 10¹²–10¹⁴ cm⁻² and Bi ions of 700 MeV at doses of 3 · 10¹²–3 · 10¹³ cm⁻² on films of stoichiometric thermal silicon dioxide, silicon dioxide films with ion-implanted excess silicon, and SiO_x films with the stoichiometric parameter x varying from 0 to 2. According to electron microscopy and Raman spectroscopy data, irradiation with the swift heavy ions resulted in the formation of silicon nanoclusters. The luminescence spectra depended on the size, number, and structure of the Si nanoclusters formed. Their size can be controlled by varying both the effect parameters (primarily, the ion energy loss per unit length of the track) and the stoichiometric composition of the films.

Conductive islands (quantum dots) of graphene and few-layer graphene in a fluorinated graphene matrix were produced by chemical functionalization of graphene in aqueous hydrofluoric acid. The structures formed were investigated by measuring the current-voltage characteristics and by means of an atomic-force microscope used to measure the surface topography and lateral forces. The presence of conductive islands in the fluorinated matrix was shown, and their sizes were determined.

The morphology and structure of CuS crystals formed during sulfidation of copper behenate films obtained by the Langmuir — Blodgett (LB) method have been studied using high resolution electron microscopy. The average size of these crystals is about 3 nm and increases by a factor of approximately 2.2 after annealing at a temperature of 150 ºC or above. Analysis of interplanar distances has shown that in the range of annealing temperatures of 150–200 ºC, CuS nanocrystals have a P6_3/mmc hexagonal crystal lattice with parameters a = 0.38 nm and c = 1.64 nm. At annealing temperatures of 250 ºC or above, the Cu₂S crystalline phase begins to form, in addition to CuS nanocrystals. The proportion of this phase increases with increasing annealing temperature. Cu₂S nanocrystals have a hexagonal crystal lattice type with the P6_3/mmc spatial group and unit cell parameters a = 0.39 nm and c = 0.68 nm. Quantitative evaluation of copper and sulfur in individual CuS and Cu₂S nanocrystals was performed by local analysis of characteristic X-ray spectra.

Current-voltage characteristics of thin dielectric films of HfO_x in p-Si/HfO_x /Ni structures are analyzed. Experimental results are compared with various theoretical models: the Poole-Frenkel trap ionization model, the multiphonon trap ionization model, and the Schottky effect at the Ni/HfO_x interface. It is shown that in spite of the good qualitative description of the experimental results by all models, only the multiphonon trap ionization model provides a quantitative description of the data.

This paper is devoted to the design and characterization of an electroosmotic pump based on asymmetric microchannel silicon membranes. A pronounced dependence of the pump flow rate on the structural asymmetry of microchannels was first found in experiments using deionized water. Pump flow rate was determined as a function of the applied voltage and the orientation of the matrix with respect to the volume of water pumped. An analytical description of the spatial structure of the microchannel matrices is proposed, which makes it possible to more accurately relate the structural and transport characteristics of the device. The data were used to calculate the zeta potential of the deionized water-silica-silicon system. It is assumed that the observed effect can be used as the basis for designing electroosmotic micropumps for modern bioanalytical micro- and nanofluidic systems.