Role of the dislocation screw component in the formation of the dislocation structure in Ge- and Si-based semiconductor heterosystems

The possibility of solving the problem of propagating dislocations in heterosystems by means of decreasing the number of dislocation families participating in the process of misfit stress relief has been investigated. The system of Γ-shaped misfit dislocations, which is proposed in the literature as the optimal type of plastic relaxation, has been analyzed. Taking into account the effect of the screw dislocation component, this suggestion is valid only for the initial stage of relaxation. The results of simulation of the process of plastic relaxation and experimental investigations of structures containing L-shaped dislocations are presented. Misfit stress relief in heterostructures grown on vicinal substrates has been theoretically and experimentally investigated.     

Ostwald ripening of nanoislands in semiconductor heterosystems and its influence on optical properties

Influence of the Ostwald ripening on character of the size distribution in semiconductor heterosystems with quantum dots as island films consisting of cylindrical, disclike islands of constant height is studied. Size distribution function and formulae for temporal changes of average island size are derived. Calculations are carried out within the LSW theory, in assumption of joint action of two (diffusion and Wagner) growing mechanisms. Comparison of the calculating results with experimental data proves validity of the accepted model approximations. Expectancy of correlation of the distribution function, growing mechanisms and properties of heterosystems is discussed.     

Effect of sound speed profile on the structure of long-range acoustic pulse

The time arrival structure of acoustic pulse signals propagating in ocean waveguides is of great significance for underwater acoustic communication and navigation. Using the deep-sea sound propagation data from the experiments respectively conducted in the East Indian Ocean(EIO) and the South China Sea(SCS) with explosion sources near the sound channel axis(SCA), long-range transmission loss(TL) and time arrival structure of acoustic pulses for different sound speed profiles(SSPs) are compared. ...     

Effect of the band structure on the thermoelectric properties of a semiconductor

The dependence of the thermoelectric parameters of a material on the band position and carrier effective masses is studied theoretically. The optimum parameters providing an increase in the thermoelectric figure-of-merit are specified. The results obtained are applied to the n-type Mg₂Si-Mg₂Sn solid solutions, in which the complex structure of the conduction band is one of the factors responsible for an increase in the thermoelectric efficiency.     

Effect of nonuniform mechanical stresses on the domain structure of iron borate

A magnetooptic method is used to study the effect of nonuniform radial mechanical stresses on the domain structure, magnetic susceptibility, and magnetic hysteresis loops of a FeBO₃ single crystal. When a magnetic field is applied in the basal plane of FeBO₃ along the stress vector, a system of tapered domains appears in the crystal during magnetization. These domains exist in a certain temperature-dependent field range H₀ ≤ H ≤ H _c . The appearance of a system of tapered domains is found to substantially affect the technical magnetization of a stressed crystal. The results obtained are discussed within the thermodynamic theory of a domain structure. A theoretical model used is shown to adequately describe the experimental temperature and field dependences of the ratio \({D \mathord{\left/ {\vphantom {D {\sqrt L }}} \right. \kern-\nulldelimiterspace} {\sqrt L }}\) (where D and L are the average width and length of a tapered domain, respectively). The calculated value of D is approximately 1.3 times smaller than the experimentally observed domain width.     

Electrodynamical treatment of the electron-hole long-range exchange interaction in semiconductor nanocrystals

We show that the contribution to the fine structure of the ground exciton level in a semiconductor nanocrystal due to the long-range part of the electron-hole exchange interaction can be equivalently described as arising from the mechanical exciton interaction with the exciton-induced macroscopic longitudinal electric field. Particular cases of nanocrystals with cubic and wurtzite crystal lattice in the strong confinement regime are studied taking into account the complex structure of the valence band. A simplified model accounting for the exciton ground-level splitting and exploiting an effective local scalar susceptibility is established.     

Role of long-range shear stresses in the plastic deformation of epitaxial films

The dependence of elastic energy on relaxation parameters ρ _x and ρ _y varying in limits from 0 to 1 is analyzed for near-surface layers of an In_0.1Ga_0.9As epitaxial film on a GaAs (001) substrate whose thickness exceeds the distance between neighboring misfit dislocations.     

Effect of short- and long-range forces on the structure of water: temperature and density dependence

The individual effects of short-range and long-range forces on the structure of water, a prerequisite for developing a perturbation theory, are assessed using a decomposition of realistic water—water potential models into trial potentials. Computer simulations for one typical liquid density and a number of temperatures ranging from the freezing temperature up to supercritical ones, and for several densities on a supercritical isotherm were performed. The trial potentials were constructed from the ST2 and TIP4P potentials and it is shown that for both potentials the results are practically identical. It is shown that (i) regardless of the thermo-dynamic conditions and potential models used, the structure of water and the mutual orientational arrangement of water molecules, given by a set of site—site correlation functions, are determined nearly exclusively only by the short range forces, and (ii) for high density states the effect of the short range electrostatic part of the intermolecular potential on the spatial arrangement of the water molecules rapidly decreases with increasing temperature but does not become negligible.     

Effect of carbon network defects on the electronic structure of semiconductor single-wall carbon nanotubes

For a single-wall (14, 0) carbon nanotube, the total density of electronic states of the ideal structure and of some possible defect structures is calculated in the framework of the band theory approach using Gaussian-type orbitals and the approximation of the generalized density gradient. It is shown that allowance for defects of the atomic structure of a nanotube makes it possible to adequately describe the existing experimental data on nanotube electronic structure. In the framework of the same approach, the total density of electronic states is calculated for an intermolecular contact of (5, 5) and (10, 0) single-wall carbon nanotubes formed due to the creation of a 5–7 defect. It is shown that the electronic states related to the contact region and the 5–7 defect lie in vicinity of the Fermi level.     

Effect of the long-range order in the vacancy distribution on the electronic structure of titanium monoxide TiO1.0

The effect of the long-range order in the vacancy distribution according to the type of monoclinic Ti₅O₅ superstructure on the electronic structure of titanium monoxide TiO _y with the stoichiometric composition has been studied by the supercell method within the DFT-GGA approximation with the use of pseudopotentials. It has been established that, in spite of an increase in the Fermi energy, the stability of the compound increases with increasing degree of the long-range order η. The ordering of the structural vacancies leads to the considerable increase in the depth of the pseudogap at the Fermi level. It has been shown that the effect of the long-range order on the electronic structure in the range of η from 0 to 1.0 is much weaker than the effect of the nonstoichiometry of TiO _y in the range of y from 0.75 to 1.33.     

Thermal stresses in layered barium titanate-based semiconductor ceramics

Thermal stresses emerging in a barium titanate-based semiconducting ceramic during heating by electric current are studied using numerical methods. It is shown that the highest tensile stresses are formed in the plane equidistant from the electrodes. The values of these stresses can be as high as 70 MPa, which is commensurate with the critical stresses. A method is proposed for reducing stresses by developing thermistors with a layered structure.     

Origins of growth stresses in amorphous semiconductor thin films

Stress evolution during deposition of amorphous Si and Ge thin films is remarkably similar to that observed for polycrystalline films. Amorphous semiconductors were used as model materials to study the origins of deposition stresses in continuous films, where suppression of both strain relaxation and epitaxial strain inheritance provides considerable simplification. Our data show that bulk compression is established by surface stress, while a subsequent return to tensile stress arises from elastic coalescence processes occurring on the kinetically roughened surface.     

Effect of interdiffusion on the band structure and absorption coefficient of a one-dimensional semiconductor superlattice

The effect of interdiffusion of Al and Ga atoms on the confining potential, band structure and absorption coefficient of electromagnetic radiation of a one-dimensional superlattice, composed of GaAs/Ga_1?x Al _x As quantum wells with the initially rectangular potential profile, is studied within the framework of the modified Wood-Saxon potential model. It is shown that the interdiffusion leads to the widening of the energy minibands and to the blueshift of the absorption spectrum observed in experiments.     

Effect of structure doping profile on the current switching-off process in power semiconductor opening switches

Using a physicomathematical model, the process of current breaking in power semiconductor opening switches was investigated in p ⁺-p-n-n ⁺ structures with different doping profiles. The model takes account of the actual doping profile of a structure, diffusion and drift of current carriers in a strong electric field, recombination via deep impurities and Auger recombination, and impact ionization in a dense plasma. The calculation of the electrical circuit of an opening switch is based on solution of Kirchhoff’s equations. It has been shown that in the nanosecond regime of breaking superhigh current densities with densities of the interrupted currents from a few to tens of kA/cm², the dominant factor in the current breaking process is the width of the p-region in the initial doping profile of a structure. An increase in the p-region width from 100 to 200 μm makes the velocity of the excess plasma front propagating in the p-region in the reverse pumping stage higher by a factor of 5–7. Higher propagation velocity of the plasma front makes the current breaking process more intensive, which is manifested in the shorter current breaking time and higher overvoltage across the opening switch.     

Effect of long-range forces on surface freezing

We examine the effect of long-range van der Waals interactions on surface freezing (SF) in linear hydrocarbon chain molecules, and the wetting criteria of the bulk liquid by the crystalline surface phase. We find that although the effect of van der Waals interactions is small for SF of normal alkanes, it is important for SF of dry and hydrated alcohols. We also find that the long-range interactions should not be ignored in the interpretation of wetting phenomena in recent experimental results. The results are in good agreement with recent experiments.     

肖特基势垒对铁磁/有机半导体结构自旋注入性质的影响

理论研究了铁磁/有机半导体肖特基接触时的电流自旋极化注入,并讨论了电流自旋极化率随界面处肖特基势垒高度、有机半导体层中特殊载流子及其迁移率、界面附近掺杂浓度的变化关系.通过计算发现,寻找在势垒区中载流子迁移率比较大的有机半导体材料对实现有效的自旋注入是必要的;同时还发现,由于铁磁/有机半导体接触而形成的肖特基势垒不利于自旋注入.因此要想实现有效的自旋注入,界面附近必须采用重掺杂来有效减少势垒区的宽度,且势垒的高度要限制在一定的范围内.     

Hydrogen on semiconductor surfaces Theory of the electronic structure

The atomic geometry and the electronic structure of GaAs(1 1 0) and Si(1 1 1) with full coverage of chemisorbed hydrogen is described in the scheme of the density functional theory and using norm-conserving pseudopotentials, as ideal prototypes of semiconductor surfaces interacting with hydrogen. The removal of relaxation or reconstruction, the bond geometry and the stretching frequencies can be described in a full ab initio approach.     

Josephson current through a ferromagnetic semiconductor/semiconductor/ferromagnetic semiconductor structure

We theoretically calculate the Josephson current for two superconductor/ferromagnetic semiconductor (SC/FS) bilayers separated by a semiconductor (SM) layer. It is found that the critical Josephson current I_C in the junction is strongly determined by not only the relative orientations of the effective exchange field of the two bilayers and scattering potential strengths at the interfaces but also the kinds of holes (the heavy or light) in the two FS layers. Furthermore, a robust approach to measuring the spin polarization P for the heavy and light holes is presented.     

Microscopic structure of semiconductor surfaces

To study the initial reaction steps of hydrogen, oxygen, and water, on differently prepared single crystal surfaces of silicon, germanium/silicon alloys, indium phosphide and gallium arsenide, we used high-resolution electron energy-loss spectroscopy (HREELS) in combination with low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Very recently, we started a program on the hydrogenation of III–V compound semiconductors, and on the oxidation of Si and III–V compound semiconductors, using alkali metals as a catalyst. This paper summarizes the present stage of our investigations, describing in particular aspects of the microscopic structure of differently prepared semiconductor surfaces.