Effect of the Ge content on the Schottky barrier height in structures based on Si1 − x Ge x solid solution

The subject of investigation is the influence of the Ge content on the Schottky barrier height in Au-p-i-n/Al structures based on Si_{1 ? x} Ge _x (0 < x < 0.26) solid solutions grown by electron-beam floating-zone melting. In Au-i-Si_{1 ? x} Ge _x , Au-αGe/Si(Li), Au-αGe/Si, and Au-n-Si_{1 ? x} Ge _x structures, the height of the barrier is about 1 eV, which exceeds the average value of this parameter for silicon available in the literature. It is shown that an excess Ge concentration in the near-surface region of the Si_{1 ? x} Ge _x crystal causes self-passivation of the surface, which leads to a rise in the barrier height. In the Au-i-Si_{1 ? x} Ge _x structures, the Schottky barrier height increases from 0.97 to 1.03 eV as Ge content x increases from 0 to 0.11.     

Magnetic phase diagram of the Ca1−xMnxO systems

The magnetic properties of the Ca_1−xMn_xO systems in the range 0?x?1 have been studied by mean field theory and high-temperature series expansions (HTSEs). By using the first theory, we have evaluated the nearest neighbour and the next-neighbour super-exchange interaction J₁(x) and J₂(x) respectively, in the range 0.45?x?1. The corresponding classical exchange energy for magnetic structure is obtained for the Ca_1−xMn_xO systems. The HTSEs combined with the Padé approximants (PA) method is applied to the Ca_1−xMn_xO systems; we have obtained the magnetic phase diagrams (TN or TSG versus dilution x) in the range 0?x?1. The obtained theoretical results are in agreement with experimental ones obtained by magnetic measurements. The critical exponents associated with the magnetic susceptibility (γ) and the correlation lengths (ν) are deduced in the range 0?x?1.     

Nanoscale distortions of the lattice of a ZnSe crystal doped with 3d elements

The structure of semiconductor crystals Zn_1?x V _x ²⁺ Se (x = 0.0018) and Zn_1?x Cr _x ²⁺ Se (x = 0.0006) was studied for the first time using thermal neutron diffraction at 300 and 120 K. The diffraction patterns of the crystals were revealed to contain diffuse scattering regions near the Bragg reflections of the initial cubic lattice. The experimental results are discussed in combination with earlier obtained data on neutron diffraction and propagation of ultrasonic waves in Zn_1?x Ni _x ²⁺ Se (x = 0.0025) and Zn_1?x Cr _x ²⁺ Se (x = 0.0029). The diffuse scattering is shown to be due to nanoscale shear strains of the ZnSe lattice. The character of these strains is determined by Jahn-Teller 3d ions.     

Features of the absorption spectra of thin films of M 2Ag1 − x CuxI3 solid solutions (M = Rb, Cs)

The absorption spectra of thin films of (MI)_{1 ? y} (Ag_{1 ? x} Cu_xI)_y solid solutions (M = Rb, Cs) with the initial molar concentration y = 0.33 have been investigated. It is established that, at low concentrations x, a local exciton band due to Cu⁺ ions is split off from the main long-wavelength exciton bands. In Rb₂Ag_{1 ? x} Cu_xI₃ solutions, the concentration shift of exciton bands indicates the formation of a persistent-type exciton spectrum. However, in Rb₂Ag_{1 ? x} Cu_xI₃ with x ≥ 0.5 and in Cs₂Ag_{1 ? x} Cu_xI₃ with x > 0.2, exciton spectra of amalgamation type are observed, which are related to the formation of more stable M ₃Ag_{2 ? 2x} Cu_2x I₅ solid solutions. The formation of these solutions leads to broadening of the exciton bands and to the concentration transition from persistent-to amalgamation-type exciton spectra.     

Long period helimagnetism in the cubic B20 FexCo1−xSi and CoxMn1−x Si alloys

We report magnetization, resistivity and small angle neutron scattering experiments on cubic B20 Fe_xCo_1?x SI alloys (0.3 ? x ? 0.9) and Co_xMn_1?xSi allpys (x = 0.02, 0.04 and 0.06). The magnetically ordered Fe_xCo_1?xSi alloys and the Co_xMn_1?xSi alloys with x = 0.02 and 0.04 are found to be helimagnetic with very long period. The low temperature resistivity of the magnetically ordered Fe_xCo_1?xSi alloys exhibits an anomalous positive magnetic contribution. The occurence of the Dzyalosyinsky-Moriya spin-orbit type interaction in these non-centrosymmetric alloys is given as a possible explanation of the helimagnetic order.     

Effect of the composition of the solid solution on the high-temperature microhardness of SiGe heteroepitaxial layers grown on Ge and Si substrates

The effect of the composition of epitaxial layers (ELs) of the Si_xGe_1?x solid solution grown on Ge and Si substrates on their microhardness and the length of dislocation rosettes forming around indentations is studied at a homologous temperature 0.5T_melt for each composition. For the Si_xGe_1?x/Ge (0≤x<0.15) and Si_xGe_1?x/Si (0.85<x≤1) ELs, the dependences of the microhardness and the length of dislocation rosettes on the solid-solution composition are nonmonotonic. The nonmonotonic change in the plasticity of the ELs is most likely caused by hardening of the solid solutions in a certain composition range due to their spinodal decomposition with the formation of clusters and disperse precipitates.     

Effects of the passivation of SiNx with various growth stoichiometry on the high temperature transport properties of the two-dimensional electron gas in AlxGa1−xN/GaN heterostructures

Effects of the passivation of SiN_x on the high temperature transport characteristics of the two-dimensional electron gas (2DEG) in unintentionally doped Al_xGa_1−xN/GaN heterostructures have been investigated by means of high temperature Hall measurements. The 2DEG density increases much after SiN_x passivation, and the increment is proportional to the Si content in SiN_x layer, indicating that the increment is mainly caused by ionized Si atoms at the SiN/Al_xGa_1−xN interface with dangling bonds or by Si atoms incorporated into the Al_xGa_1−xN layer during the SiN_x growth, which is approved by strain analysis and X-ray photoemission spectroscopy (XPS). There is lower 2DEG mobility at room temperature in a passivated sample than in an unpassivated one. However, the 2DEG mobility becomes to be higher in a passivated sample than in an unpassivated one when the temperature is above 250 °C, which is suggested to be caused by different subband occupation ratios in the triangular quantum well at the heterointerface before and after passivation.     

Phase analysis of the system La1−x Ba x FeO3−y (0≦x≦0.70) by means of x—ray diffraction and Mössbauer spectroscopy

X-ray diffraction and Mössbauer measurements were performed on novelly synthesized La_1?x Ba _x FeO_3?y (0≤x≤0.70). Two phases were found in the system. La_1?x Ba _x FeO_3?y for 0≤x≤0.10 is an orthorhombic perovskite. La_1?x Ba _x FeO_3?y for 0.54≤x≤0.70 is a cubic perovskite. La_1?x Ba _x FeO_3?y for 0.10≤x≤0.54 consists of these two phases.     

Influence of the presence of Co on the rare earth solubility in M-type hexaferrite powders

Sr_1−xRE_xFe₁₂O₁₉ and Sr_1−xRE_xFe_12−xCo_xO₁₉ (x=0–0.4 and RE=Pr, Nd) M-type hexaferrite powders were produced according to a conventional ceramic process. The X-ray diffraction analysis of the calcinated material reveals the presence of secondary α-Fe₂O₃, PrFeO₃ or NdFeO₃ and CoFe₂O₄ phases in substituted samples, with proportions that increase with x. However, for the same x value, the proportion of secondary phases is lower in Co-containing powders than in Co-free powders. This indicates that the presence of Co in the M-type phase increases the solubility of the rare earth. The results of the Mössbauer investigation indicate that the solubility of Pr is higher than that of Nd in Co-containing samples.     

On the transfer of line radiation in random magnetic fields

An analysis is made of the influence of a magnetic field of constant magnitude but with random orientations, described by the spherical coordinates θ and φ, on the polarization transfer in spectral lines. The assumption that the statistical properties of the field are determined by the one- and two-point probability densities P₁(x, θ, φ) and P₂(x₁, θ₁, φ₁; x₂, θ₂, φ₂) where x is the coordinate along the ray, implies that the variations of θ and φ can be considered as being due to a Markovian process in x. The expectation values of the Stokes parameters 〈Iγ〉, γ = 1, …4, are calculated functions of x or the optical depth τ. The formalism includes the limiting cases of infinite and zero correlation length. Assuming an artificial triplet and simple conditions, the results suggest that isotropic magnetic fields of the type considered have no influence on the polarization characteristics during the transfer.     

Influence of Fe-doping on the structural,optical and magnetic properties of ZnO nanoparticles

Zn_1–xFe_xO (x=0–0.05) nanoparticles were synthesized without a catalyst by a two-step method. Fe was doped into ZnO by a source of metallic Fe sheets in a solid–liquid system at 80 °C, and the Zn_1−xFe_xO nanoparticles were obtained by annealing at 300 °C. X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy were used to characterize the structural properties of the as-grown Zn_1−xFe_xO. The optical properties were determined by Infrared and Ultraviolet–visible spectroscopy. The results confirm that the crystallinity of the ZnO is deteriorated due to Fe-doping. XPS results show that there is a mixture of Fe⁰⁺ and the Fe³⁺ in the representative Zn_0.95Fe_0.05O sample. The optical band gap of Zn_1−xFe_xO is enhanced with increasing of Fe-doping. Room temperature ferromagnetism was observed in all the Fe-doped ZnO samples.     

The influence of actinides on the superconducting properties of molybdenum chalcogenides

The results of the investigations of molybdenum chalcogenides: U_xPb_1?xMo₆S₈, U_xPb_1?xMo_6.4S₈, Th_xPb_1?xMo₆S₈, U_x1?xMo₆S₈ with actinides as a component, are presented. As a rule the decrease of superconducting parameters with x was observed. Possible influence of magnetic interaction in this system is noted.     

Transition from the Kondo regime to long-range magnetic order in the FexV1−x S system

A study is reported on the electrical and magnetic characteristics of the Fe_xV_1?x S solid-solution system with x≤0.5. A maximum in the temperature dependence of resistivity ρ(T) characteristic of the Kondo effect has been observed for small x(x<0.01). For x>0.1, long-range magnetic order sets in in the system with T _K ≈ 100 K. Near x=0.05, the Fe²⁺ impurity behavior crosses over to a magnetically ordered phase. The electronic properties of Fe_xV_1?x S are typical of those of strongly correlated electronic systems. Both the electrical and magnetic data imply that carrier delocalization is the strongest at x=0.4.     

On the characteristics of AlGaN films grown on (111) and (001) Si substrates

High Al-content Al_xGa_1−xN films were deposited on (001) and (111) Si substrates at 1000 °C using high temperature AlN buffer layers. Experimental results show that Al_xGa_1−xN films grown on (111) Si substrates exhibit better crystalline quality than that in the films deposited on (001) Si substrates. Cracks were found in the high Al-content Al_xGa_1−xN/(111) Si samples but they were not observed in the Al_xGa_1−xN films grown on (001) Si substrates having the same film thicknesses and Al compositions. Based upon the results of X-ray diffraction (XRD) and transmission electron microscopy (TEM), it appears that mono-crystalline Al_xGa_1−xN films were achieved on (111) Si substrates while columnar structure was observed in the Al_xGa_1−xN/(001) Si samples. According to the depth profiles of Al_xGa_1−xN/Si samples using secondary ion mass spectroscopic (SIMS) analyses, enhanced Al inter-diffusion in the Al_xGa_1−xN/(001) Si samples was identified. Room temperature (RT) photoluminescence (PL) measurements of the Al_xGa_1−xN (x≦0.10)/(111) Si samples exhibit strong near band edge luminescence. The PL emission linewidth was found to decrease with the decrement of Al-content.     

Theoretical study of the electronic and magnetic properties of Co2Cr1−xVxAl

We have investigated the electronic and magnetic properties of the doped Heusler alloys Co₂Cr_1−xV_xAl(x=0, 0.25, 0.5, 0.75, 1) using first-principles density functional theory within the generalized gradient approximation (GGA) scheme. The calculated results reveal that with increasing V content the lattice parameter slightly increases; both cohesive energy and bulk modulus increase with increasing x. The magnetic moment of the Co(Cr) sites increases with V doping; the total spin moment of these compounds linearly decreases. We also have performed the electronic structure calculations for Co₂Cr_1−xV_xAl with positional disorder of Co-Y(Cr,V)-type and Al-Y(Cr,V)-type. It is found that formation of Al-Y-type disorder in Co₂Cr_1−xV_xAl alloys is more favorable than that of Co-Y-type disorder. Furthermore, we found that Co₂Cr_1−xV_xAl of the L2₁-type structure have a half-metallic character. And the stability of L2₁ structure will enhance, however, the Curie temperature decreases as the V concentration increases. The disorder between Cr(V) and Al does not significantly reduce the spin polarization of the alloys Co₂Cr_1−xV_xAl.     

Pressure experiment determination of the direct-indirect transition in the quarternary In1−xGaxP1−zAsz

Spontaneous and laser emission from In_1-xGa_xP_1-zAs_z double heterojunction diodes near the direct-indirect crossover (E_Γ = E_X, x ≡ x_c, z ≡ z_c) are studied at 77°K as a function of hydrostatic pressure up to 6 kbar. The pressure coefficients of the spontaneous emission peaks and of the laser modes are ～- 10.5 × 10^-6 eV/bar which is characteristics of the Γ band edge in III–V semiconductors. Laser threshold current is found to rise rapidly as pressure is applied owing to the decreasing Γ-X separation and the resultant carrier transfer to the X minima. Experimental lower limits for the direct-indirect crossover at three points in the In_1-xGa_xP_1-zAs_z quaternary system are determined. These three points and the established crossover in GaAs_1-yP_y (y_c ≈ 0.46, 77°K) give for the quaternary crossover (77°K) x_c ? 0.52z_c = 0.72. and the value x_c ≈ 0.72 for the limiting case of In_1-xGa_xP. Band edge bowing effects along the direct-indirect crossover in the In_1-xGa_xP_1-zAs_z system are discussed. The highest energy laser (77°K) for this quaternary system is estimated from pressure measurements to be ～ 2.155 eV (5752 Å).     

Chiral-odd transversity spin structure function h1(x) of the nucleon in a constituent quark model

We study the chiral-odd transversity spin-dependent quark distribution function h₁(x) of the nucleon in a constituent quark model. The twist-2 structure functions, f₁(x), g₁(x) and h₁(x) are calculated within the diquark spectator approximation. Whereas an inequality f₁(x) > h₁(x) > g₁(x) holds with the interaction between quark and diquark being scalar, the axial-vector effective quark-diquark interaction, which contributes to the d-quark distribution, does not lead to such a simple relation. We find that h₁(x) for the d-quark becomes somewhat smaller than g₁^d(x), when we fix the model parameter to reproduce known other structure functions. We also include corrections due to the non-trivial structure of the constituent quark, which is modeled by the Goldstone boson dressing. This improves agreements of f₁(x) and g₁(x) with experiments, and brings further reduction of h₁^d(x) distribution. Consequences for semi-inclusive experiments are also discussed.     

Structure of the intermediate high-pressure phases of ternary lead tellurides

In chambers with diamond anvils, the structure of high-pressure phases of ternary lead tellurides Pb_1?x Sn_xTe (x = 0.29) and Pb_1?x Mn_xTe (x = 0.05) and nonstoichiometric crystals Pb_0.55Te_0.45, Pb_0.45Te_0.55 is analyzed by the synchrotron radiation diffraction method at pressures of P up to 14 GPa. The orthorhombic structure of the intermediate high-pressure phase (space group Pnma) is determined for all the samples above 6 GPa. Models of the phase transition in PbTe from the initial rock salt structure to the orthorhombic phase, which constitutes a distorted variant of NaCl, as well as the properties of this phase, are discussed.     

GdGd interaction and frequency dependence of the ESR linewidth in metallic GdxY1−xP,GdxSc1−xP and GdxY1−xAs

We have investigated the frequency dependence of the high temperature ESR linewidth of the metallic rare earth pnictides Gd_xY_1?xP, Gd_xSc_1?xP and Gd_xY_1?xAs (1?x?0.2) from 9 up to 71 GHz. The Gd pnictides represent a group of compounds where the Korringa relaxation rate, which in most metals and metallic compounds determines the ESR linewidth, is unusually small. Thus, the behaviour of the linewidth can be discussed in terms of exchange narrowing of dipolar contributions.     

Structural and magnetic studies of the alloy system GdInxAg1-x

The structural and magnetic studies below room temperature of the alloy system GdIn_xAg_1-x(0?x?1) are reported. It has been found that alloys with x?0.5 crystallize in CsCl type cubic structure, but the distortion of the unit cell starts for alloys with x#62;0.5 and for these alloys the unit cell becomes tetragonal. No phase change is evident from the low temperature (295-8 K) structural studies. However, a break appears in the X^-1_m vs. T linear plot of each alloy of this system at a specific temperature (designated as break temperature T_B). The variation of T_B with x is similar to the variation of phase transition temperature with x reported for LaIn_xAg_1-x. Close agreement has been found in the values of effective magneton number (p), magnetic ordering [Néel (T_N) or Curie (T_C)] and paramagnetic Curie (θ_p) temperature for materials studied by us and earlier workers. The variation of magnetization with applied field strength (2.5-65)×10⁵ Am^-1) at 4.2 K has also been reported for ferromagnetic of this system. It has been concluded that alloys with 0.4?x?0.6 are simple ferromagnets with parallel alignment of magnetic moment in the ground state. The angular arrangement of the magnetic moment starts appearing in the ground state for alloys with x?0.4 for x#62;0.6 and continues till x becomes closure to 0.17 or 0.84. The alloys with x=0.17 or x=0.84 have θ_p and T_C equal to zero and appear paramagnetic. Angular arrangement in spins again appear for alloys with x?0.17 or x#62;0.84, however all materials with 0?x?0.17 or 0.84?x?1 remain antiferromagnetic.