Polarization dependence of intersubband absorption and photoconductivity in p-type SiGe quantum wells

We present a detailed study of the polarization dependence of subband absorption and photoconductivity in Si/SiGe quantum wells. For samples with a hole concentration ofp_s2.8×10¹² cm², bothp- ands-polarized absorptions have been observed and transitions to several excited states are clearly identified by comparison with self-consistent Luttinger-Kohn type calculations. The photoconductivity is surprisingly insensitive to the polarization, which indicates the importance of the subsequent transport process on the photocurrent responsitivity.     

Shubnikov-de Haas effect of n-inversion layers in InSb grain boundaries

Hall effect and Shubnikov-de Haas effect have been investigated in a n-inversion layer adjacent to the grain boundary in p-InSb bicrystals. The observed quantum oscillations of the magnetoconductivity result from a superposition of the Shubnikov-de Haas effect in two occupied subbands. The electron densities of the subbands n_si(n_s1=3.5 × 10¹¹cm^-2;n_s0= 1.1 × 10¹²cm^-2) and the effective cyclotron mass of the lower subband m_c0=(0.023 ± 0.002)m₀ have been evaluated.     

Transport properties of n-type ferromagnetic semiconductor HgCr2−xInxSe4(x = 0.100)

Measurements of the electrical conductivity, magnetoresistance, and Hall effect were performed on a n-type ferromagnetic semiconductor HgCr_2?xIn_xSe₄(x = 0.100) single crystal from 6.3 to 296 K in magnetic fields up to 1.19×l0⁶A/m. The conductivity decreases rapidly near the Curie temperatureT_c (≈120 K) as the temperature is raised. A large peak in the magnetoresistance is observed near T_c. The Hall effect measurements indicate that the temperature dependence of the conductivity and the magnetoresistance are due mostly to a change in electron mobility. The electron mobility is 1.2 × 10^?2 m²/V · s at 6.3 K, and decreases rapidly near T_c with the rise in temperature. Then it increases slowly from 5.5 × 10^?4 m²/V · s at 160 K to 7.5 × 10^?4 m²/V · s at 241 K. This temperature dependence of the electron mobility can be explained in terms of the spin-disorder scattering which takes into account the exchange interaction between charge carriers and localized magnetic moments.     

C-V characterization of Schottky- and MIS-gate SiGe/Si HEMT structures

Electrical properties of Schottky- and metal-insulator-semiconductor (MIS)-gate SiGe/Si high electron mobility transistors (HEMTs) were investigated with capacitance-voltage (C-V) measurements. The MIS-gate HEMT structure was fabricated using a SiN gate insulator formed by catalytic chemical vapor deposition (Cat-CVD). The Cat-CVD SiN thin film (5 nm) was found to be an effective gate insulator with good gate controllability and dielectric properties. We previously investigated device characteristics of sub-100-nm-gate-length Schottky- and MIS-gate HEMTs, and reported that the MIS-gate device had larger maximum drain current density and transconductance (g_m) than the Schottky-gate device. The radio frequency (RF) measurement of the MIS-gate device, however, showed a relatively lower current gain cutoff frequency f_T compared with that of the Schottky-gate device. In this study, C-V characterization of the MIS-gate HEMT structure demonstrated that two electron transport channels existed, one at the SiGe/Si buried channel and the other at the SiN/Si surface channel.     

Oxidation process of SiGe on SOI substrates

The oxidation of SiGe film epitaxial grown on top of SOI wafers has been studied. These SiGe/SOI samples were oxidized at 700, 900, 1100 °C. Germanium atoms were rejected from SiGe film to SOI layer. A new Si_1−xGe_x (x is minimal) layer formed at SiGe/Si interface. As the germanium atoms diffused, the new Si_1−xGe_x (x is minimal) layer moved to Si/SiO₂ interface. Propagation of threading dislocation in SiGe film to SOI substrate was hindered by the new SiGe/Si interface. Strain in SOI substrate transferred from SiGe film was released through dislocation nucleation and propagation inner. The relaxation of SiGe film could be described as: strain relaxed through strain equalization and transfer process between SiGe film and SOI substrates. Raman spectroscopy was used to characterize the strain of SiGe film. Microstructure of SiGe/SOI was observed by transmission electron microscope (TEM).     

Strain-induced anodization of SiGe/Si multiple layers to form high density SiGe/Si heterogeneous nanorods

SiGe/Si heterogeneous nanostructures are prepared by electrochemical anodization of SiGe/Si multiple layers grown by ultra-high vacuum chemical vapor deposition. Nanorods with densities up to ～2×10¹¹ cm^?2 have been observed with a relatively uniform distribution confirmed by scanning electron microscope images of both top and cross-sectional views. The samples show visible photoluminescence with multiple peaks and narrow widths which is related to the interference effect. Finally, a model is proposed to explain the role of strain during the anodization of SiGe/Si multiple layers.     

Isospin-two ππ phase shifts from an experiment π+p→π+n at 12.5 GeV/c

The I = 2 s-wave and d-wave phase shifts σ_s²and σ_d² have been determined in the ππ mass region 0.5–1.5 GeV/c² in four mass bins of width 0.25 GeV/c², using a sample of 17 500 events from a wire chamber experiment. Two different methods were used, leading to consistent results.In the ?-mass region δ_s² ? ?15.5°, which corresponds to an elastic cross section of ? 7.5 mb. The values of δ_d² are about a factor of ten smaller than the corresponding values of δ_s².     

Calculation of X-ray and Auger transition rates, lifetimes, X-ray wavelengths, and fluorescence yields of variously ionized silicon atoms

X-ray and Auger transition rates, X-ray wavelengths, and fluorescence yields are calculated for variously ionized silicon atoms with configurations 1s2s^m2pⁿ, m=0-2, n=1-6. The calculation has been performed using the Hartree-Fock atomic model. Intermediate coupling and configuration interaction have been taken into account. The energies and widths are found to be strongly affected by configuration mixing. The results from the present calculation have been compared with those available in the literature. The theoretical K_α hypersatellite and satellite spectra fall into several well-separated regions, corresponding to each of the possible number of spectator electrons in the 2s and 2p shells. The dependence of radiative rates and fluorescence yields on the number of spectator electrons is also investigated.     

Optical mode softening in the incommensurate phase of Sr2Nb2O7

In the incommensurate phase below about 220°C of Sr₂Nb₂O₇, the soft mode, of which frequency decreases toward 215°C has been found by the Raman scattering measurements in the $\text{b(cc)}\text{b}$ scattering geometry. The level repulsion and the intensity transfer between the soft mode and another low frequency mode are clearly observed. The uncoupled soft mode frequency ω_s has been found to be expressed as ω_s =A(T_tr?T)^β, where β= 0.38 ± 0.02. Pressure dependence of the soft mode has also been measured up to 24kbar. No remarkable pressure dependence has been observed.     

The missing mass squared dependence of the average charged particle multiplicity in the reaction K+p → KoX++ from 5–16 GeV/c

The average charged particle multiplicity, 〈n_ch(M_X²)〉, in the reaction K⁺p→K^oX⁺⁺ is studied as a function of the mass squared, M_X², of the recoil system X and also as a function of the K^o transverse momentum, p_T, at incident momenta of 5.0, 8.2 and 16.0 GeV/c. The complete data samples yield distributions which are not independent of c.m. energy squared, s, They exhibit a linear dependence on log (M_X²_X/M_o²)[M_o²=1 GeV²] with a change in slope occurring for M_X²≈s/2, and do not agree with the corresponding distributions of 〈n_ch〉 as a function of s for K⁺ p inelastic scattering. Sub-samples of the data for which K^o production via beam fragmentation, central production and target fragmentation are expected to be the dominant mechanisms show that, within error, the distribution of 〈n_ch(M_X²)〉 versus M_X² is independent of incident momentum for each sub-sample separately. In particular in the beam fragmentation region the 〈n_ch(M_X²)〉 versus M_X² distribution agrees rather well with that of 〈n_ch〉 versus s for inelastic K⁺p interactions. The latter result agrees with recent results on the reactions pp → pX and π^?p → pX in the NAL energy range. Evidence is presented for the presence of different production mechanisms in these separate regions.     

Electron-hole liquid and excitonic molecules in quasi-two-dimensional SiGe layers of Si/SiGe/Si heterostructures

The electron-hole liquid (EHL) in SiGe layers of Si/Si_{1 − x} Ge _x /Si quantum-confinement heterostructures is discovered. It is composed of quasi-two-dimensional holes in the quantum well formed by the SiGe layer and quasi-three-dimensional electrons, which occupy a wider region of space centered on this layer. The densities of electrons and holes in the EHL are determined to be p ₀ ≈ 8.5 × 10¹¹ cm⁻² and n ₀ ≈ 4.8 × 10¹⁸ cm⁻³, respectively. It is demonstrated that the gas phase consists of excitons and excitonic molecules. The conditions on the band parameters of the structure under which the formation of the EHL of this kind and biexcitons is possible are formulated.     

Quark masses

We review the current information about the eigenvalues of the quark mass matrix. The theoretical problems involved in a determination of the running masses m_u, m_d, m_s, m_c and m_b from experiment are discussed with the aim of getting reliable numerical values equipped with error bars that represent a conservative estimate of remaining uncertainties.     

Mechanism of formation of cellular dislocation structures during propagation of intense shock waves in crystals

The mechanism of formation of a cellular dislocation structure in face-centered cubic (fcc) metal crystals subjected to shock compression at strain rates \(\dot \varepsilon \) > 10⁶ s^?1 has been considered theoretically within the dislocation kinetic approach based on the kinetic equation for the dislocation density (dislocation constitutive equation). A dislocation structure of the cellular type is formed in the case of a two-wave structure of the compression wave behind its shock front (elastic precursor). It has been found that, at pressures σ > 10 GPa, the dislocation cell size Λ _c depends on the pressure σ and the density ρ _G of geometrically necessary dislocations generated at the shock front according to the relationship Λ _c ～ ρ _G ^?n ～ σ^?m , where n = 1/4–1/2, m = 3/4–3/2, and m = 1, for different pressures and orientations of the crystal. It has been shown that, in copper and nickel crystals with the shock loading axis oriented along the [001] direction, the cellular structure is not formed after reaching the critical pressures σ _c equal to 31 and 45 GPa, respectively.     

Electrical properties of narrow gap semiconductor PtSb2

Results of measurements of conductivity, Hall and Seebeck coefficients of tellurium doped n-type crystals of platinum antimonide are presented. The Hall coefficient and the Seebeck coefficient undergo sign inversion twice, below and above room temperature. The detailed analysis of the experimental results revealed that below 200 K PtSb₂ can be described by a simple conduction and valence band model. The energy gap E_g = (110?0.15 × T) (meV), the electron conductivity mass m_n^c/m₀ = 0.35, acoustic phonon limited electron mobility 〈μ_a〉_n = 3 × 10⁶ T^{?$\text{3}\text{2}$} ($\text{cm}{}^2\text{V · s}$) and mobility ratio 〈μ_a〉_n/〈μ_a〉_p = 0.4 are determined. However, at higher temperatures a more complicated valence band model is needed to account for the experimental results. The arguments for the existence of subsidiary valleys in the valence band are presented.     

Exact compositional analysis of SiGe alloys by matrix effect compensated MCs+-SIMS

SiGe alloy, owing to its high electron and hole mobility, has potential applications in high-speed microelectronic device technology. The optimization of such technology requires the precise determination of Ge concentration in the full range of composition and the understanding and control of the Ge–Si interdiffusion phenomenon. The most appropriate analytical technique with highest detection sensitivity (～subparts per billion) for measuring elemental concentration is secondary ion mass spectrometry (SIMS). However, strong compositional dependence of secondary ion yield, i.e. “matrix effect,” has always made SIMS quantification extremely difficult. A procedure for the accurate quantification of Ge concentration in molecular beam epitaxy (MBE)-grown Si_1?x Ge _x (0<x<0.72) alloys based on MCs⁺-SIMS approach has been proposed. The “matrix effect” is shown to be completely suppressed for all Ge concentrations irrespective of impact Cs⁺ ion energies. The novel methodology has successfully been applied for direct quantitative composition analysis of Si/Ge multilayer structure.     

Universal correlations, pseudo‐gaps and condensation mechanisms in high‐Tc superconductors

We combine universal correlations between T_c and n_s/m^* (superconducting carrier density/effective mass) found by μSR with the pseudo gap behavior found in the underdoped region by various techniques to develop a picture for explaining doping dependence of high‐T_c superconductivity in terms of a crossover from Bose–Einstein to BCS condensation. μSR results in overdoped and Zn‐substituted systems suggest that behavior on the high‐density side is more complicated than expected in a simple BCS model. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inelastic collisions between excitons in semiconductors—I: Collisions with excited final states

The exciton-exciton (Exc-Exc) inelastic collision cross sections for the different semiconductors CdS, ZnO, CdSe, Si and Cu₂O have been calculated in the Born approximation. The simple transitions Exc (1s/B) + Exc (1s/A)→ Exc (1s/B) + Exc (nl /A) where nl = 2s, 2p, 3s, 3p and 3d have been The calculations are carried out as functions of the different available values of σ = m¹_e/m¹_h where m¹ and m¹_h are, respectively, the electron and the hole effective masses for the corresponding semiconductors.     

Correlations betweenT c andn s/m * (carrier density/ effective mass) in high-T c and organic superconductors

We update our muon spin relaxation studies of the magnetic field penetration depth which show the correlations betweenT _c and the relaxation rate σ αn _s/m ^* (carrier density/effective mass) of hole-doped high-T _c cuprate superconductors (La₂, Sr₃)CuO₄, YBa₂Cu₃O₇ (Y_1−xPr_x)Ba₂Cu₃O₇, and other double and triple layer systems. These studies are extended to the organic superconductor (BEDT-TTF)₂Cu(NCS)₂.     

Surface cyclotron resonance in Si under uniaxial stress

The cyclotron resonance of inversion-layer electrons on (100)p-type Si is found to depend sensitively on an externally applied compressive stress. At low temperatures (T ? 10 K) we observe a considerable increase of the cyclotron mass m¹_c with stress S along the [001] direction. The effect is most strongly observed at low electron densities n_s. For $\text{S～1.5 × 10}{}^9\text{dyne}\text{cm}{}^2$ and n_s～2 × 10¹¹cm^-2 we obtain $\text{m}{}^1{}_{\mathrm{c}}\text{～0.4 m}{}_0$ instead of the expected 0.2m₀. Along with this change of $\text{m}{}^1{}_{\mathrm{c}}$ a strong narrowing of the resonance is noted. Raising the temperature gives an additional n_s- dependent increase of $\text{m}{}^1{}_{\mathrm{c}}$.     

Measurement of π−p → π0n at large momentum transfer

New results on a high statistics measurement of pion-nucleon charge exchange scattering at 40 GeV/c, extending in momentum transfer up to ?t = 1.8 (GeV/c)², are reported and compared with an optical impact parameter model, together with previous data for the reaction π^?p → ηn at the same energy. The imaginary part of the pole trajectory b₀(s) is determined from the slope of the tangent to the maxima of $\text{(?t)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{d}\text{σ}\text{d}\text{t}$. The linear increase of Im b₀(s) with log s, which has been observed at low energies, continues up to 40 GeV/c.