Synthesis of carbon planar structures with specified properties

A new method is proposed that allows an integrated technology to be used for the synthesis of carbon planar structures with predetermined properties. The method is based on the avalanche annealing of amorphous short-period superlattices. The synthesized samples are investigated by Raman spectroscopy and photoluminescence. The possibility of synthesizing carbon layers with diamond-like, graphite-like, graphene, or other structures is demonstrated experimentally using the example of a C/SiC superlattice.     

The influence of AlN/GaN superlattice intermediate layer on the properties of GaN grown on Si（111） substrates

AlN/GaN superlattice buffer is inserted between GaN epitaxial layer and Si substrate before epitaxial growth of GaN layer. High-quality and crack-free GaN epitaxial layers can be obtained by inserting AlN/GaN superlattice buffer layer. The influence of AlN/GaN superlattice buffer layer on the properties of GaN films are investigated in this paper. One of the important roles of the superlattice is to release tensile strain between Si substrate and epilayer. Raman spectra show a substantial decrease of in-plane tensile strain in GaN layers by using AlN/GaN superlattice buffer layer. Moreover, TEM cross-sectional images show that the densities of both screw and edge dislocations are significantly reduced. The GaN films grown on Si with the superlattice buffer also have better surface morphology and optical properties.     

Particular nanowire superlattice as a spin filter

A nanowire superlattice of InAs and GaAs layers with In_0.47Ga_0.53As as the impure layers is proposed. The oft-neglected k³ Dresselhaus spin-orbit coupling causes the spin polarization of the electron but often can produce a limited spin polarization. In this nanowire superlattice, Dresselhaus term produce complete spin filtering by optimizing the distance between the In_0.47Ga_0.53As layers and the Indium (In) in the impure layers. The proposed structure is an optimized nanowire superlattice that can efficiently filter any component of electron spins according to its energy. In fact, this nanowire superlattice is an energy dependent spin filter structure.     

Green function method for ferromagnetic superlattice

The expression of Green function for different layers in a ferromagnetic superlattice is derived by the recurrence relations technique. The elementary unit cell of the superlattice under consideration consists of alternating layers of two simple-cubic Heisenberg ferromagnets. The results are illustrated numerically for a particular choice of parameters.     

应变弛豫InGaAs/GaAs超晶格的X射线双晶衍射及形貌研究

应用X射线双晶衍射及双晶形貌术,对应变弛豫的InGaAs/GaAs超晶格作了研究,通过对双晶衍射摇摆曲线的计算机模拟,得到了超晶格的结构,应变弛豫机制,弛豫比,超晶格层与衬底的取向差等重要参数。从双晶形貌,得到了超晶格与衬底界面处和超晶格中的位错分布。 关键词：     

Soliton delay line based on a semiconductor superlattice

A new type of delay line intended for soliton pulses is proposed. As a nonlinear medium, a semiconductor superlattice is taken. Solitons that propagate along the superlattice layers are confined in cells bounded by transverse inhomogeneity layers. Solitons are confined and released with the help of an external electric current passing inside the cell.     

The defect structure of AlGaN/GaN superlattices grown on sapphire by the MOCVD method

High-resolution x-ray diffractometry and electron microscopy are used to study the defect structure and relaxation mechanism of elastic stresses in AlGaN/GaN superlattices grown by the MOCVD method on sapphire covered with a preliminarily deposited GaN and AlGaN buffer layer. Based on an analysis of the half-widths of three-crystal scan modes of x-ray reflections measured in different diffraction geometries, the density of different dislocation families is determined. For all the dislocation families, the density is shown to increase with the Al concentration in the solid-solution layers and depend only weakly on the superlattice period. From the electron-microscopic patterns of planar and cross sections, the types of dislocations and their distribution in depth are determined. It is shown that, in addition to high-density vertical edge and screw dislocations, which nucleate in the buffer layer and propagate through the superlattice layers, there are sloped intergrowing dislocations with a large horizontal projection and bent mixed dislocations with a Burgers vector $\left\langle {11\overline 2 3} \right\rangle $ at the interface between individual superlattice layers. The former dislocations form at the interface between the buffer layer and the superlattice and remove misfit stresses between the buffer and the superlattice as a whole, and the latter dislocations favor partial relaxation of stresses between individual superlattice layers. In samples with a high Al concentration (greater than 0.4) in AlGaN layers, there are cracks surrounded by high-density chaotic horizontal dislocations.     

Transformation of the polariton spectrum of nonideal topologically ordered superlattices

The transformation of the polariton spectrum of a nonideal superlattice (a one-dimensional crystal with two elements, layers, in a unit cell) caused by the presence of randomly embedded foreign (with respect to an ideal superlattice) impurity layers is investigated in the framework of the virtual crystal approximation. The obtained specific features of the energy gap as a function of concentration for different values of the polariton branch number testify that the energy structure of the superlattice can be changed significantly by embedding certain impurities into it.     

Determination of strain in epitaxial semiconductor structures by high-resolution X-ray diffraction

High-resolution X-ray diffraction is used to obtain the strain profile of a wide range of epitaxial semiconductor samples. The samples are divided into five categories: Strained layers on a substrate, (partly) relaxed layers on a substrate, strained-layer superlattice structures, multiple relaxed layers and relaxed superlattice structures and ionimplanted samples. For each category a measurement strategy and analysis method is given. Representative examples for each category are shown.     

Infrared absorption and Raman scattering on coupled plasmon-phonon modes in superlattices

We theoretically consider a superlattice formed by thin conducting layers spatially separated between insulating layers. The dispersion of two coupled phonon-plasmon modes of the system is analyzed by using the Maxwell equations, with the retardation effect included. Both transmission for the finite plate and the absorption for the semi-infinite superlattice in the infrared are calculated. Reflectance minima are determined by the longitudinal and transverse phonon frequencies in the insulating layers and by the density-state singularities of the coupled modes. We also evaluate the Raman cross section from the semi-infinite superlattice. The text was submitted by the authors in English.     

On the correction of errors in quantum cryptography systems

The Raman and photoluminescence spectra of short-period C/SiC superlattices produced by RF magnetron sputtering are investigated. The Raman data indicate that, in 35-period Sitall/Ni/[C/SiC] superlattices with the C and SiC effective thicknesses of 3.5 and 3 Å, respectively, subjected to postgrowth avalanche annealing, the carbon layers assume the structure of multilayer graphene with 3–5 graphene sheets per superlattice period. A method for the fabrication of graphene-like carbon structures on the basis of short-period superlattices grown by RF sputtering is suggested and implemented.     

Energy spectrum and effective mass of carriers in the InSe/GaSe superlattice

Within an effective mass approximation the energy spectrum and mass of carriers in the InSe/GaSe superlattice have been calculated. The superlattice belongs to type II: electrons are primarily confined to the InSe layers whereas the holes are mosfly confined to the GaSe layers. The characteristic feature of electronic structure of the superlattice is the existence of minibands of light carriers at the θ point of the Brillouin zone and minibands of heavy carriers at theM point. The dependence of the miniband structure on thickness of layers has been computed. It is shown that the minibands of light and heavy carriers compete with one another in energy. A general conclusion is made concerning the influence of the competition between the minibands on optic and kinetic properties of the superlattice.     

Influence of interdiffusion of heteromaterials on X-ray diffraction by superlattice with stacking fault

X-ray dynamic diffraction on a superlattice with a stacking fault between the layers is considered theoretically in the case of interdiffusion of superlattice components. Expressions for the X-ray reflectance within satellite limits, depending on the wave’s phase jump on the stacking fault, its depth and the extent of interdiffusion of superlattice components are obtained.     

Energy spectrum and effective mass of carriers in the InSe/GaSe superlattice

Within an effective mass approximation the energy spectrum and mass of carriers in the InSe/GaSe superlattice have been calculated. The superlattice belongs to type II: electrons are primarily confined to the InSe layers whereas the holes are mosfly confined to the GaSe layers. The characteristic feature of electronic structure of the superlattice is the existence of minibands of light carriers at the θ point of the Brillouin zone and minibands of heavy carriers at theM point. The dependence of the miniband structure on thickness of layers has been computed. It is shown that the minibands of light and heavy carriers compete with one another in energy. A general conclusion is made concerning the influence of the competition between the minibands on optic and kinetic properties of the superlattice.     

Effect of negative acoustic refraction in a one-dimensional phononic crystal

A two-component thin-layer acoustic superlattice (one-dimensional phononic crystal), in which one of the layers of the superlattice period is near the proper ferroelastic phase transition, is considered. The necessary conditions under which a bulk elastic wave incident on the outer surface of the superlattice excites a refracted wave with negative acoustic refraction (at the fundamental or multiple frequency) have been determined.     

Radiofrequency magnetoresistance of Fe/Cr superlattices

The rf magnetoresistance of Fe/Cr superlattices is studied for two orientations of the current: parallel and across the superlattice layers. A mutually single-valued correspondence is established between the relative magnetoresistance measured at dc current and the change in the transmission coefficient of electromagnetic waves in the magnetic field. When rf currents flow across the layers, the relative change in the signal amplitude is proportional to twice the change in the electrical resistance of the superlattice and is of opposite sign. It is shown that the rf losses are determined by the surface resistance which is proportional to the superlattice thickness and inversely proportional to its conductivity. An equation is derived for the rf electric field distribution in the superlattice. It is established that when the thickness of the superlattice is small compared with the skin layer depth, field and current components which penetrate through the entire superlattice exist.     

Anisotropy of long-wavelength optical phonons in GaAs/AlAs superlattices

The angular anisotropy of optical phonons in GaAs/AlAs (001) superlattices is investigated by Raman scattering spectroscopy. Scattering configurations allowed for phonons with wave vectors oriented along the superlattice layers and normally to them are used. For phonons localized in GaAs layers, the theoretically predicted mixing of the LO1 longitudinal modes with TO1 transverse modes in which atomic displacements occur along the normal to the superlattice is observed experimentally. These modes possess noticeable angular anisotropy. For transverse modes in which atoms move in the plane of the superlattice, the angular anisotropy is small.     

Efficient spin filtering in a disordered semiconductor superlattice in the presence of Dresselhaus spin-orbit coupling

The influence of the Dresselhaus spin-orbit coupling on spin polarization by tunneling through a disordered semiconductor superlattice was investigated. The Dresselhaus spin-orbit coupling causes the spin polarization of the electron due to transmission possibilities difference between spin up and spin down electrons. The electron tunneling through a zinc-blende semiconductor superlattice with InAs and GaAs layers and two variable distance In_xGa_(1−x)As impurity layers was studied. One hundred percent spin polarization was obtained by optimizing the distance between two impurity layers and impurity percent in disordered layers in the presence of Dresselhaus spin-orbit coupling. In addition, the electron transmission probability through the mentioned superlattice is too much near to one and an efficient spin filtering was recommended.     

Microwave-assisted synthesis of Cu2ZnSnS4 nanocrystals as a novel anode material for lithium ion battery

One-dimensional ordered quantum-ring chains are fabricated on a quantum-dot superlattice template by molecular beam epitaxy. The quantum-dot superlattice template is prepared by stacking multiple quantum-dot layers and quantum-ring chains are formed by partially capping quantum dots. Partially capping InAs quantum dots with a thin layer of GaAs introduces a morphological change from quantum dots to quantum rings. The lateral ordering is introduced by engineering the strain field of a multi-layer InGaAs quantum-dot superlattice.     

Imaging the evolution of lateral composition modulation in strained alloy superlattices

Scanning tunneling microscopy is used to investigate the morphological evolution of GaAs/InAs short period superlattice structures. The layers of the superlattice, either grown in compression or tension, exhibit an island or trench morphology. With increasing film thickness, the islands or trenches grow in size and develop a characteristic spacing along [110] of approximately 150 A. This is the first experimental evidence to suggest that lateral composition modulation arises from both thickness variations of the layers and compositional nonuniformities within the atomic plane.