Effect of Doping on the Properties of Hydrogenated Amorphous Silicon Irradiated with Femtosecond Laser Pulses

A comparative analysis of the effect of femtosecond laser irradiation on the structure and conductivity of undoped and boron-doped hydrogenated amorphous silicon (a-Si: H) is performed. It is demonstrated that the process of nanocrystal formation in the amorphous matrix under femtosecond laser irradiation is initiated at lower laser energy densities in undoped a-Si: H samples. The differences in conductivity between undoped and doped a-Si: H samples vanish almost completely after irradiation with an energy density of 150–160 mJ/cm².     

Bemerkungen über relativistische Stoßinvarianten

The relativistic analogue of the theorem ofGrad is proven stating that the general additive collision invariant is given by the expressionβ _a p ^a +c. It is used to determine the equilibrium distribution of a 1-component general relativistic quantum gas. The proof is not analogous to the one initially given byGrad, but covers the non-relativistic case.     

Coulomb oscillations of the current through spin-nondegenerate <Emphasis Type="Italic">p</Emphasis> states of InAs quantum dots

The electron transport is studied in split-gate structures fabricated on the basis of a modulation-doped heterostructure that contains a single quantum well and self-assembled InAs quantum dots near the 2D electron gas regions. The current passing through the channel with a denumerable set of InAs quantum dots is found to exhibit Coulomb oscillations as a function of the gate voltage. The oscillations are associated with the excited p states of InAs quantum dots, which are characterized by opposite spins and caused by lifting of the spin degeneracy of the p state due to the Coulomb interaction. The Coulomb oscillations of the current are observed up to a temperature of ～20 K. The Coulomb energy is found to be ΔE_c = 12.5 meV, which agrees well with the theoretical estimates for the p states of quantum dots in the structures under study.     

Inflation of the early cold Universe filled with a nonlinear scalar field and a nonideal relativistic Fermi gas

We consider a possible scenario for the evolution of the early cold Universe born from a fairly large quantum fluctuation in a vacuum with a size a ₀ ? l _P (where l _P is the Planck length) and filled with both a nonlinear scalar field φ, whose potential energy density U(φ) determines the vacuum energy density λ, and a nonideal Fermi gas with short-range repulsion between particles, whose equation of state is characterized by the ratio of pressure P(n _F ) to energy density ε(n _F ) dependent on the number density of fermions n _F . As the early Universe expands, the dimensionless quantity ν(n _F ) = P(n _F )/ε(n _F ) decreases with decreasing n _F from its maximum value ν_max = 1 for n _F → ∞ to zero for n _F → 0. The interaction of the scalar and gravitational fields, which is characterized by a dimensionless constant ξ, is proportional to the scalar curvature of four-dimensional space R = κ[3P(n _F )–ε(n _F )–4λ] (where κ is Einstein’s gravitational constant), and contains terms both quadratic and linear in φ. As a result, the expanding early Universe reaches the point of first-order phase transition in a finite time interval at critical values of the scalar curvature R = R _c =–μ²/ξ and radius a _c ? a ₀. Thereafter, the early closed Universe “rolls down” from the flat inflection point of the potential U(φ) to the zero potential minimum in a finite time. The release of the total potential energy of the scalar field in the entire volume of the expanding Universe as it “rolls down” must be accompanied by the production of a large number of massive particles and antiparticles of various kinds, whose annihilation plays the role of the Big Bang. We also discuss the fundamental nature of Newton’ gravitational constant G _N .     

Amplitude-phase reflectance spectra of amorphous silicon-based Bragg structures

Amplitude-phase spectra of light reflection from distributed Bragg reflectors and Fabry-Pérot microcavities based on a-Si: H/a-SiO_x: H thin films have been studied. The frequency dependence of the phase difference between the amplitude p-and s-light reflection coefficients within the photonic band gap is measured. The phase spectrum exhibits predominantly a monotonic, close-to-linear frequency behavior, except for spectral regions near the stop band edges and near the singularities related to the microcavity eigenmodes. The experimental spectra are compared with theoretical calculations based on the transfer matrix method and approximate analytical relations. A method based on analyzing amplitude-phase reflectance spectra is proposed for structural characterization of multilayer microcavity systems.     

Mechanism of charge transfer in <Emphasis Type="Italic">n</Emphasis>-CdS/<Emphasis Type="Italic">p</Emphasis>-CdTe heterojunctions

The capacitance-voltage and current-voltage characteristics of the n-CdS/p-CdTe heterosystem are investigated. Analysis of these characteristics demonstrates that the CdTe_1?x S _x solid solution formed at the n-CdS/p-CdTe heterointerface is inhomogeneous in both the conductivity and composition. The thickness of solid solutions is estimated from the capacitance-voltage characteristics. It is shown that, for the n-CdS/p-CdTe heterosystem, the current-voltage characteristic in the current density range 10^?8-10^?5 A cm^?2 is governed by the thermal electron emission, whereas the current in the heterostructure at current densities in the range 10^?4-10^?2 A cm^?2 is limited by recombination of charge carriers in the electroneutral region of the CdTe_1?x S _x solid solution. The lifetime and the diffusion length of minority charge carriers in the CdTe_1?x S _x solid solution and the surface recombination rate at the interface between the CdS layer and the CdTe_1?x S _x solid solution are determined. It is demonstrated that the n-CdS/p-CdTe heterostructure operates as a p-i-n structure in which CdTe is a p layer, CdTe_1?x S _x is an i layer, and CdS is an n layer.     

Doppler three-level (V-scheme) laser without population inversion

The theory of amplification and lasing without population inversion in a three-level medium with inhomogeneous broadening via the formation of an open V configuration is elaborated. The conditions for energy transfer from the infrared into the visible spectral range, i.e., the conditions of up-conversion n _b >n _c >n _a , and the external field required for saturation of the b?a transition are established. Two-photon resonant Raman transitions in ensemble of mobile atoms of a gas-discharge plasma are analyzed. The frequency shift of the probe field spectrum as a whole is shown to be governed by the frequency shift of the pump field multiplied by the ratio of the wave numbers of the probe amplification field and the pump field. The interaction of atoms through Ne transitions with the pump field (λ=1.15 εm, 2p ₄-2s ₂ transition) and the lasing field (λ=0.6328 εm, 3s ₂-2p ₂ transition) with an increase in the lasing frequency by a factor of 1.82 with respect to the absorbed radiation is calculated.     

On the structure of strips exhibiting the integral quantum Hall effect in an inhomogeneous 2D electron system

A formalism is developed to generalize the results obtained for “incompressible” strips exhibiting the integral quantum Hall effect in a spatially inhomogeneous 2D electron system to the cases of finite temperatures, significant electron density gradients, etc. Specifically, the concept of the “quality” of a given integer quantum Hall effect strip (channel) is introduced; the quality is proportional to the derivative dn(x)/dx in the central part of the channel [n(x) is the electron density distribution over the channel]. For a well-defined channel, this derivative tends to zero. If a noticeable gradient arises in the n(x) distribution, the channel does not exhibit the quantum Hall effect and ceases to exist. The conditions are determined under which a channel exhibiting the integral quantum Hall effect breaks down. The results of calculations are used to interpret the available experimental data.     

Dependence of structure factor and correlation energy on the width of electron wires

The structure factor and correlation energy of a quantum wire of thickness b ? a _B are studied in random phase approximation (RPA) and for the less investigated region r _s < 1. Using the single-loop approximation, analytical expressions of the structure factor are obtained. The exact expressions for the exchange energy are also derived for a cylindrical and harmonic wire. The correlation energy in RPA is found to be represented by ? _c (b, r _s ) = α(r _s )/b + β(r _s ) ln(b) + η(r _s ), for small b and high densities. For a pragmatic width of the wire, the correlation energy is in agreement with the quantum Monte Carlo simulation data.     

Room Temperature Spin Accumulation Effect in Boron Doped Si Created by Epitaxial Fe<Subscript>3</Subscript>Si/<Emphasis Type="Italic">p</Emphasis>-Si Schottky Contact

To study spin-dependent transport phenomena in Fe₃Si/p-Si structures we fabricated 3-terminal planar microdevices and metal/semiconductor diode using conventional photolithography and wet chemical etching. I?V curve of prepared diode demonstrates rectifying behavior, which indicates the presence of Schottky barrier in Fe₃Si/p-Si interface. Calculated Schottky barrier height is 0.57 eV, which can provide necessary conditions for spin accumulation in p-Si. Indeed, in 3-terminal planar device with Fe₃Si/p-Si Schottky contact Hanle effect was observed. By the analysis of Hanle curves spin lifetime spin diffusion length in p-Si were calculated, which are 145 ps and 405 nm, respectively (at T = 300 K). Spin lifetime strongly depends on temperature which can be related to the fact that spin-dependent transport in our device is realized via the surface states. This gives a perspective of creation of spintronic devices based on metal/semiconductor structure without need for forming tunnel or Schottky tunnel contact.     

Powerful diode nanosecond current opening switch made of <Emphasis Type="Italic">p</Emphasis>-silicon (<Emphasis Type="Italic">p</Emphasis>-SOS)

The nanosecond semiconductor diode-based opening switch (SOS-diode) capable of switching currents with densities up to several tens of kiloamperes per cubic centimeter represents a p⁺p’Nn⁺ silicon structure fabricated by the deep simultaneous diffusion doping (to about 200 μm) of n-Si by Al and B from one side and P from the other. In the SOS mode, first a short pulse of forward current passes through the diode and then a fast-growing pulse of reverse voltage is applied. A resulting pulse of reverse current carries away injected holes and thereby forms a plasma front in the p’ layer, which moves toward the p’N junction. When the hole concentration in the flow exceeds the dopant concentration in the p’ layer, a space charge region arises in this layer, the resistivity of the diode increases sharply, and the current switches to a load connected parallel to the diode. Early results concerning an alternative configuration of the SOS diode are presented. Here, the diode was made by the rapid simultaneous diffusion of B and P from the opposite sides of a p-Si wafer to a depth of 60-80 μm. If a short pulse of forward current is passed through such a p⁺pn⁺ structure and a pulse of reverse voltage is then applied, a plasma front arising in the p⁺ region moves toward the p⁺p interface through the heavily doped (i.e., low-resistivity) p⁺ region. Having crossed this interface, the front passes into a low-doped region, where the hole concentration in the flow becomes much higher than the dopant concentration and a space charge region causing the current to pass to the load forms at once. It is shown experimentally that, all other things being the same, the time of current breaking in the p-SOS-diode is roughly twice as short as in the conventional n-SOS-diode, switched currents are considerably lower, and the fabrication technique of p-SOS-diodes is much simpler. Ways of optimizing the design of the semiconductor structure of the p-SOS-diode to further raise the speed are outlined.     

The real solution to scalar field equation in 5D black string space

After the nontrivial quantum parameters Ω _n and quantum potentials V _n obtained in our previous research, the circumstance of a real scalar wave in the bulk is studied with the similar method of Brevik and Simonsen (Gen. Rel. Grav. 33:1839, 2001). The equation of a massless scalar field is solved numerically under the boundary conditions near the inner horizon r _e and the outer horizon r _c . Unlike the usual wave function Ψ_ωl in 4D, quantum number n introduces a new functions Ψ_{ωl n} , whose potentials are higher and wider with bigger n. Using the tangent approximation, a full boundary value problem about the Schrödinger-like equation is solved. With a convenient replacement of the 5D continuous potential by square barrier, the reflection and transmission coefficients are obtained. If extra dimension does exist and is visible at the neighborhood of black holes, the unique wave function Ψ_{ωl n} may say something to it.     

Exclusive electrodisintegration of the deuteron within the point form of relativistic quantum mechanics

The process of exclusive deuteron electrodisintegration is considered within the point form of relativistic quantum mechanics. Relevant calculations are performed on the basis of the Nijmegen and Moscow nucleon-nucleon potentials, the latter involving forbidden states. Final-state interaction is taken into account. For either type of the potentials used, the results of the calculations describe well experimental data at final-neutron momenta p _n of up to 500 MeV/c.     

Structural transformations of K<Subscript>3</Subscript>H(SO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystals with variations in temperature

Single crystals of the K₃H(SO₄)₂ compound are investigated using X-ray diffraction on Xcalibur S and Bruker diffractometers. The structure of the low-temperature monoclinic phase is refined (space group C2/c, z = 4, a = 14.698(1) Å, b = 5.683(1) Å, c = 9.783(1) Å, β = 103.01(1)°, T = 293 K, Bruker diffractometer), the structural phase transition is revealed, and the structure of the high-temperature trigonal phase is determined (space group R \(\bar 3\) m, z = 3, a = 5.73(1) Å,c = 21.51(1) Å,T = 458 K, Xcalibur diffractometer).     

Coulomb Rydberg electron <Emphasis Type="Italic">L</Emphasis>-mixing in collisions with atomic ions

The cross sections of the Rydberg electron L-mixing in a hydrogen atom and a hydrogen-like ion are calculated for slow collisions with atomic ions H*(n, L) + A⁺ = H*(n, L′) + A⁺ without variation of the principal quantum number n. The probability of the L-mixing L → L′ is associated with the quantum interference of the wave functions of adiabatic states, i.e., with the mixing of the time phases of these functions exp(?i∫E _k (t)dt). The effective cross section of such L-mixing for the states with n = 28 are 4–5 orders of magnitude greater than the cross sections determined in previous investigations. The expansion coefficients of spherical Coulomb wave functions in terms of parabolic ones and vice versa, which are necessary for determining cross sections, are calculated on the basis of a comprehensive analysis of the spatial properties of these functions.     

Structure and electrophysical properties of ferrocobaltites <Emphasis Type="Italic">Ln</Emphasis>BaFeCoO<Subscript>5 + δ</Subscript> (<Emphasis Type="Italic">Ln</Emphasis> = Tb,Dy, Ho,Y)

The ferrocobaltites LnBaFeCoO^{5 + δ} (Ln = Tb, Dy, Ho, Y) have been synthesized, and the parameters of their crystal structure have been determined. The thermal expansion, electrical resistivity ρ, and thermopower S of the synthesized compounds have been investigated in air at temperatures in the range from 300 to 1100 K. The compounds have a tetragonal structure (symmetry space group P4/mmm) with the unit cell parameters a = 3.9000 Å and c = 7.5922 Å (Ln = Tb, δ = 0.31), a = 3.8973 Å and c = 7.5679 Å (Ln = Dy, δ = 0.34), a = 3.8970 Å and c = 7.5507 Å (Ln = Ho, δ = 0.28), and a = 3.9029 Å and c = 7.5538 Å (Ln = Y, δ = 0.25). The ferrocobaltites under investigation are p-type semiconductors, and their electrical resistivity ρ and thermopower S decrease in the sequence Tb → Ho → Y → Dy (at room temperature). The linear thermal expansion coefficient of the LnBaFeCoO^{5 + δ} phases in the vicinity of the temperatures ranging from 465 to 535 K increases from (1.15?1.23) × 10^?5 to (1.73?1.93) × 10^?5 K^?1. The parameters of charge transfer in these ferrocobaltites have been determined. It has been found that an increase in the temperature leads to an increase in the excitation energy of charge carriers and a decrease in the activation energy of charge carrier transfer.     

Generation of dislocation loops in strained quantum dots embedded in a heterolayer

The generation of prismatic dislocation loops in strained quantum dots is investigated. The quantum dots are embedded in a film-substrate heterostructure with mechanical stresses caused by the difference between the lattice parameters of the film (heterolayer) and the substrate. The intrinsic plastic strain ?_m of a quantum dot arises from the misfit between the lattice parameters of the materials of the quantum dot and the surrounding matrix. The interface between the heterolayer and the substrate is characterized by a misfit parameter f. The critical radius of a quantum dot R _c at which the generation of a dislocation loop in the quantum dot becomes energetically favorable is analyzed as a function of the intrinsic plastic strain ?_m and the misfit parameter f.     

Properties of magnesium silicate doped with chromium in porous silicon

Forsterite doped with Cr⁴⁺ ions is prepared in silicon-based structures according to a simple technique. These structures are of interest due to the characteristic luminescence in the near-IR range. Forsterite is synthesized by impregnation of porous silicon layers on n⁺-Si and p⁺-Si substrates with subsequent annealing in air. A photoluminescence response at a wavelength of 1.15 μm is observed at room temperature in porous silicon layers doped with magnesium and chromium for which the optimum annealing temperature is close to 700°C. The photoluminescence spectrum of porous silicon on the p⁺-Si substrate contains a broad band at a wavelength of approximately 1.2 μm. This band does not depend on the annealing temperature and the magnesium and chromium content and is most likely associated with the presence of dislocations in silicon. The experimental EPR data and eletrical properties of the structures are discussed. It is found that layers of pure porous silicon and chromium-doped porous silicon on n⁺-Si subtructures exhibit indications of discrete electron tunneling.     

Tripartite Quantum Controlled Teleportation via Seven-Qubit Cluster State

In this paper, a theoretical scheme for tripartite quantum controlled teleportation is presented using the entanglement property of seven-qubit cluster state. This means that Alice wants to transmit a entangled state of particle a to Bob, Charlie wants to transmit a entangled state of particle b to David and Edison wants to transmit a entangled state of particle c to Ford via the control of the supervisor. In the end, we compared the aspects of quantum resource consumption, operation complexity, classical resource consumption, quantum information bits transmitted, success probability and efficiency with other schemes.     

Hall coefficient in heavy fermion metals

Experimental studies of the antiferromagnetic (AF) heavy fermion metal YbRh₂Si₂ in a magnetic field B indicate the presence of a jump in the Hall coefficient at a magnetic-field tuned quantum state in the zero temperature limit. This quantum state occurs at B ≥ B_c0 and induces the jump even though the change of the magnetic field at B = B_c0 is infinitesimal. We investigated this by using the model of heavy electron liquid with the fermion condensate. Within this model, the jump takes place when the magnetic field reaches the critical value B_c0 at which the ordering temperature T_N(B = B_c0) of the AF transition vanishes. We show that at B → B_c0, this second order AF phase transition becomes the first order one, making the corresponding quantum and thermal critical fluctuations vanish at the jump. At T → 0 and B = B_c0 the Grüneisen ratio as a function of the temperature T diverges. We demonstrate that both the divergence and the jump are determined by the specific low temperature behavior of the entropy \(S(T) \propto S_0 + a\sqrt T + bT\) with S₀; a and b are temperature independent constants.