Magnetic moment relaxation of a shallow acceptor center in heavily doped silicon

Results of studying the temperature dependence of the residual polarization of negative muons in crystalline silicon with germanium (9×10 ¹⁹ cm ^?3 ) and boron (4.1×10 ¹⁸ , 1.34×10 ¹⁹ , and 4.9×10 ¹⁹ cm ^?3 ) impurities are presented. It is found that, similarly to n-and p-type silicon samples with impurity concentrations up to ～10 ¹⁷ cm ^?3 , the relaxation rate ν of the magnetic moment of a _μ Al acceptor in silicon with a high impurity concentration of germanium (9×10 ¹⁹ cm ^?3 ) depends on temperature as ν～T ^q , q≈3 at T=(5–30) K. An increase in the absolute value of the relaxation rate and a weakening of its temperature dependence are observed in samples of degenerate silicon in the given temperature range. Based on the experimental data obtained, the conclusion is made that the spin-exchange scattering of free charge carriers makes a significant contribution to the magnetic moment relaxation of a shallow acceptor center in degenerate silicon at T?30 K. Estimates are obtained for the effective cross section of the spin-exchange scattering of holes (σ _h ) and electrons (σ _e ) from an Al acceptor center in Si: σ _h ～10^?13 cm² and σ _e ～8×10^?15 cm² at the acceptor (donor) impurity concentration n _a (n _d )～4×10¹⁸ cm^?3.     

Exciton spectra and electrical conductivity of epitaxial silicon-doped GaN layers

Optical spectra and electrical conductivity of silicon-doped epitaxial gallium nitride layers with uncompensated donor concentrations N _D — N _A up to 4.8 × 10¹⁹ cm^?3 at T ≈ 5 K have been studied. As follows from the current-voltage characteristics, at a doping level of ～3 × 10¹⁸ cm^?3 an impurity band is formed and an increase of donor concentration by one more order of magnitude leads to the merging of the impurity band with the conduction band. The transformation of exciton reflection spectra suggests that the formation of the impurity band triggers effective exciton screening at low temperatures. In a sample with N _D — N _A = 3.4 × 10¹⁸ cm^?3, luminescence spectra are still produced by radiation of free and bound excitons. In a sample with N _D — N _A = 4.8 × 10¹⁹ cm^?3, Coulomb interaction is already completely suppressed, with the luminescence spectrum consisting of bands deriving from impurity-band-valence band and conduction-band-valence band radiative transitions.     

N2-broadening coefficients of methyl chloride at room temperature

Methyl chloride is of interest for atmospheric applications, since this molecule is directly involved in the catalytic destruction of ozone in the lower stratosphere. In a previous work [Bray et al. JQSRT 2011;112:2446], lines positions and intensities of self-perturbed ¹²CH₃³⁵Cl and ¹²CH₃³⁷Cl have been studied into details for the 3.4 μm spectral region. The present work is focused on measurement and calculation of N₂-broadening coefficients of the ¹²CH₃³⁵Cl and ¹²CH₃³⁷Cl isotopologues. High-resolution Fourier Transform spectra of CH₃Cl–N₂ mixtures at room-temperature have been recorded between 2800 and 3200 cm^?1 at LADIR (using a classical source) and between 47 and 59 cm^?1 at SOLEIL (using the synchrotron source on the AILES beamline). 612 mid-infrared transitions of the ν₁ band and 86 far-infrared transitions of the pure rotational band have been analyzed using a multispectrum fitting procedure. Average accuracy on the deduced N₂-broadening coefficients has been estimated to 5% and 10% in the mid- and far-infrared spectral regions, respectively. The J- and K-rotational dependences of these coefficients have been observed in the mid-infrared region and then a simulation has been performed using an empirical model for 0≤J≤50, K≤9. The ¹²CH₃³⁵Cl–N₂ line widths for 0≤J≤50 and K≤10 of the ν₁ band and for 55≤J≤67 and K≤15 of the pure rotational band have been computed using a semi-classical approach involving exact trajectories and a real symmetric-top geometry of the active molecule. Finally, a global comparison with the experimental and theoretical data existing in the literature has been performed. Similar J- and K-rotational dependences have been appeared while no clear evidence for any vibrational or isotopic dependences have been pointed out.     

Line strengths,spin-splittings,and forbidden transitions in the (101) band of 14N16O2

Measurements of line strengths in the (101) and (111)-(010) bands of ¹⁴N¹⁶O₂ have been made at a resolution of 0.02 cm^?1 in the region 2863 to 2934 cm^?1. The strength data in the (101) band were analyzed to determine a vibrational band strength and coefficients of the F factor. Each subband for K_?1 ≤ 9 was analyzed separately and all the F-factor coefficients in terms of the rotational quantum number, N, were found to be too small to be of significance. However, F was found to be dependent on K_?1 and the experimentally determined subband strengths were least-squares fitted to the expression S_v⁰·F, where S_v⁰ = 68.3 cm^?2 atm^?1 at 296 K and F = 1 + (2.899 × 10^?3)K_?1 + (4.08 × 10^?3)K_?1² ? (2.34 × 10^?4)K_?1³. The integrated strengths for the (101) and (111)-(010) bands were found to be 70.9 ± 2.3 and 2.7 ± 0.3 cm^?2 atm^?1 at 296 K, respectively. Also included in this study are measurements of line center positions in the two bands and spin-splittings in the (101) band. Recent frequency measurements of lines with K_?1 ≤ 8 in the (101) band have been made at a resolution of 0.0033 cm^?1 by V. Dana and J. P. Maillard (J. Mol. Spectrosc.71, 1–4) (1978)) for the region above 2889 cm^?1 and our values are in excellent agreement with theirs. Separations of the split lines measured in this work (K_?1 ≤ 10) agree well with calculated values using expressions which include the η_aaaaK_?1⁴ term with η′_aaaa = ?1.70 ± 0.15 × 10^?4 cm^?1 as derived for the (101) state. Three forbidden (ΔN ≠ ΔJ, ΔK_?1 = 0) transitions in the (101) band were observed with their identifications based on the agreement between measured and calculated line positions and strengths.     

Determination of the electron concentration and temperature,as well as the reduced electric field strength,in the plasma of a high-voltage nanosecond discharge initiated in atmospheric-pressure nitrogen by a runaway electron beam

We report on the results of spectroscopic measurements of electron concentration N _e and temperature T _e , as well as the reduced electric field strength E/N in the plasma of a high-voltage nanosecond discharge in the gap with a strongly nonuniform electric field distribution, which is filled with nitrogen under the atmospheric pressure. The possibility of using the method for determining T _e and E/N, which is based on the determination of the ratio of the peak intensities of the ionic N ₂ ⁺ (λ = 391.4 nm) and molecular N₂ (λ = 394 nm) nitrogen bands, is proved. We detected the mean values of quantities N _e , T _e , and E/N amounting to ～2 × 10¹⁴ cm^?3, ～2 eV, and ～240 Td, respectively. In addition, the dynamics of these quantities is determined.     

The vibrational numbering and improved constants of the A3Π1u state of I2

The A-X system of I₂ has been recorded in absorption, under conditions of medium resolution, over the region 8000 – 13 400 Å. Bandheads in progressions based on v″ = 6 through 18 have been measured and assigned. A new vibrational numbering for the A state is proposed, which leads to more reliable values for the important constants of the A state: T_e = 10 906 ± 3 cm^?1, D_e = 1641 ± 3 cm^?1, ω_e = 92.5 ± 0.5 cm^?1, ω_ex_e = 1.20 ± 0.08 cm^?1, ω_ey_e = ?0.062 ± 0.006 cm^?1.     

The AE-XA1 System of CaOCH3

We have recorded laser excitation spectra of the CaOCH₃ free radical in a laser ablation molecular beam apparatus, at a spectral resolution of about 0.010 cm⁻¹ and a rotational temperature estimated at 15 K. The two spin-orbit components of the A²E-X²A₁ 0₀⁰ origin band between 625 and 630 nm have been analyzed. Five main subbands were revealed, with ΔK=+1 and K″=0,±1,±2. There was clear evidence of lambda-doubling in the A²E_1/2-X²A₁ 0₀⁰ (F′₁) K′=+1←K″=0 component. A nonlinear least-squares fitting program based on the model developed by Endo et al. [Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys.81, 122-135 (1984)] fit the experimental data (514 A-X lines, N″≤37) with a root mean square deviation of 0.003 cm⁻¹, using known molecular constants of the ground state. The main vibronic (T₀=15 925.1232(5) cm⁻¹), spin-orbit (aζ_ed=66.974 48(51) cm⁻¹), Coriolis (Aζ_t=5.437 30(24)) cm⁻¹, rotational (A=5.439 97(24) cm⁻¹, B=0.117 884(2) cm⁻¹), and fine structure constants (ε₁=−8.208(14)×10⁻³ cm⁻¹, h₁=1.50(12)×10⁻⁴ cm⁻¹, ε_aa=3.58(89)×10⁻³ cm⁻¹, ε_bc=3.20(76)×10⁻³ cm⁻¹) for the excited state have been obtained.     

Optical spectra of (CdF2)0.9(InF3)0.1 semiconductor solid solutions

The differences in the optical spectra of CdF₂:In semiconductors with bistable DX centers (concentrated (CdF₂)_0.9(InF₃)_0.1 solid solutions) and “standard” samples with a lower impurity concentration used to record holograms are discussed. In contrast to the standard samples, in which complete decay of two-electron DX states and transfer of electrons to shallow donor levels may occur at low temperatures, long-term irradiation of a (CdF₂)_0.9(InF₃)_0.1 solid solution by UV or visible light leads to decay of no more than 20% deep centers. The experimental data and estimates of the statistical distribution of electrons over energy levels in this crystal give the total electron concentration, neutral donor concentration, and concentration of deep two-electron centers to be ～5 × 10¹⁸ cm^?3, ～9 × 10¹⁷ cm^?3, and more than 1 × 10²⁰ cm^?3, respectively. These estimates show that the majority of impurity ions are located in clusters and can form only deep two-electron states in CdF₂ crystals with a high indium content. In this case, In³⁺ ions in a limited concentration (In³⁺ (～9 × 10¹⁷ cm^?3) are statistically distributed in the “unperturbed” CdF₂ lattice and, as in low-concentrated samples, form DX centers, which possess both shallow hydrogen-like and deep two-electron states.     

The 2880-Å emission spectrum of I2: Ion-pair states near 47 000 cm−1

An emission system of I₂ in Ar in the region 2830–2890 Å is examined under high resolution and found to display fine violet-degraded band structure. This system is interpreted as a charge-transfer transition originating from an ion-pair state near 47 000 cm^?1 and terminating on a weakly bound state which dissociates to two ground-state atoms. This interpretation is supported by spectral simulations employing a bound-free model. The transition is tentatively assigned as $\text{0}{}_{\mathrm{<mtext>g</mtext>}}{}^{\mathrm{?}}\text{→ 2431 0}{}_{\mathrm{<mtext>u</mtext>}}{}^{\mathrm{?}}\text{(}{}^3\text{Π}\text{)}$, according to which the excited state becomes the fourth ion-pair state near 47 000 cm^?1 to be experimentally characterized, and the lower state is the last component of the lowest ³Π state to be identified. The vibrational assignments include about 45 bands in ¹²⁷I₂ and ¹²⁹I₂, spanning v′ = 0–4 and v″ = 6–19, but with the numbering of the lower state remaining uncertain by several units. The main spectroscopic constants for the excited state are T_e = 47 070 cm^?1, ?_e = 105.7 cm^?1, ?_ex_e = 0.49 cm^?1. The spectral simulations place the lower state's potential curve 34 650 cm^?1 below the upper state at R = R′_e, with slope ?850 cm^?1/Å. For our “best” numbering of the lower state, ?_e = 20.5 cm^?1, ?_ex_e = 0.29 cm^?1, T_e = 12 190 cm^?1, and D_e = 360 cm^?1.     

Photoluminescent studies of the condensed phase in phosphorus-doped silicon

Photoluminescent studies give evidence for the existence of the electron—hole droplet in phosphorus-doped silicon in the impurity concentration range 9.0 × 10¹⁵cm^?3 ? N_D ? 4.3 × 10¹⁹cm^?3.     

X-ray spectroscopic diagnostics of ultrashort laser-cluster interaction at the stage of the nonadiabatic scattering of clusters

X-ray spectroscopic diagnostics of laser-cluster interaction at the stage of nonadiabatic scattering of clusters and formation of a spatially uniform plasma channel has been performed. The experimental investigations have been carried out on a Ti:Sa laser setup with a pulse duration of about 65 fs and an energy up to 600 mJ. It has been shown that, within 10 ps from the beginning of a laser femtosecond pulse, the laser-cluster interaction forms a uniform plasma channel with a length of 0.4 to 1 mm with the parameters N _e ～ 10¹⁹?10²⁰ cm^?3 and T _e ～ 100 eV.     

The contribution of dissociative processes to the production of atomic lines in hydrogen plasmas

The contribution of molecular dissociative processes to the production of atomic lines is considered for a steady-state hydrogen plasma. If the contribution of dissociative processes is dominant, a substantial simplification in plasma diagnostics can be achieved. Numerical calculations have been performed for the production of Balmer α, β, and γ lines in hydrogen plasmas with medium and large degrees of ionization (x ? 10^-4) and for 5000 ? T_e, K ? 45,000 and 10¹⁰ ? N_e, cm^-3 ? 10¹⁶.     

Study of some rare decays of the K+ meson

In a search for very rare decays of the K⁺ meson we observed the K⁺→μ⁺νe⁺e^? and K⁺→e⁺ν e⁺e^? modes with branching ratios of (10±3) ×10^?7 and (2⁺²_?2)×10^?7 respectively. We also put new limits on a decay allowed by the alternate scheme of lepton conservation K⁺→π^?μ⁺e⁺, on a decay with double charged weak current K⁺→π^? e⁺e⁺ and on other forbidden decays K⁺→μ^?νe⁺e⁺ and K⁺→π⁺μ^±e^±.     

Vibrational analysis of the A′1Π state of barium oxide using two isotopes

Barium vapor is reacted with N₂¹⁶O and N₂¹⁸O at 0.7 Torr to produce clearly distinguishable isotopic bands of BaO A′¹Π-X¹Σ in the wavelength region of 320–415 nm. The unique vibrational numbering is determined by measuring the isotopic shift in the bandheads between Ba¹⁶O and Ba¹⁸O. Spectroscopic constants for the A′¹Π state are determined from the present analysis to be ν₀₀ = 17 588 ± 15 cm^?1, ω_e = 442.45 ± 0.3 cm^?1, and ω_ex_e = 1.652 ± 0.009 cm^?1. Uncertainties represent three standard deviations.     

Stark broadening of lines from multiply-charged carbon ions in a high-density arc plasma

Profiles of C(III) and C(IV) lines emitted in the VUV and visible regions from a pulsed arc (N_e=1.5×10¹⁸ cm^-3, T_e=5.3×10⁴K) have been measured with time resolution. The experimental results are in satisfactory agreement with the predictions of electron impact theory for (3-3) and (3-4) transitions for which the energy separation between the upper level and the nearest perturbing level is smaller than the electron thermal energy. For lines from (2-2) transitions for which the plasma is optically thick, damping constants determined experimentally agree with theoretical values within a factor of two.     

Spectroscopic study of plasma during electrolytic oxidation of magnesium- and aluminium-alloy

We present the results of an optical emission spectroscopy study of Plasma during Electrolytic Oxidation (PEO) of magnesium- and aluminum-alloy. Plasma electron number density N_e diagnostics is performed either from the H_β line shape or from the width or shift of non-hydrogenic ion lines of aluminum and magnesium. The line profile analysis of the H_β suggests presence of two PEO processes characterized by relatively low electron number densities N_e≈1.2×10¹⁵ cm^?3 and N_e≈2.3×10¹⁶  cm^?3. Apart from these two low N_e processes, there is the third one related to the ejection of evaporated anode material through micro-discharge channels. This process is characterized by larger electron density N_e=(1.2–1.6)10¹⁷ cm^?3, which is detected from the shape and shift of aluminum and magnesium singly charged ion lines. Two low N_e values detected from the H_β and large N_e measured from the widths and shift of ion lines suggest presence of three types of discharges during PEO with aluminum- and magnesium-alloy anode. On the basis of present and earlier results one can conclude that low N_e processes do not depend upon anode material or electrolyte composition.The electron temperature of 4000 K and 33,000 K are determined from relative intensities of Mg I and O II lines, respectively. The attention is drawn to the possibility of N_e application for T_e evaluation using Saha equation what is of importance for PEO metal plasma characterization. During the course of this study, difficulties in the analysis of spectral line shapes are encountered and the ways to overcome some of the obstacles are demonstrated.     

Magnetic field effects on the nonohmic impurity conduction of uncompensated crystalline silicon

The impurity conduction of a series of crystalline silicon samples with the concentration of major impurity N ≈ 3 × 10¹⁶ cm^?3 and with a varied, but very small, compensation K was measured as a function of the electric field E in various magnetic fields H-σ(H, E). It was found that, at K < 10^?3 and in moderate E, where these samples are characterized by a negative nonohmicity (dσ(0, E)/dE < 0), the ratio σ(H, E)/σ(0, E) > 1 (negative magnetoresistance). With increasing E, these inequalities are simultaneously reversed (positive nonohmicity and positive magnetoresistance). It is suggested that both negative and positive nonohmicities are due to electron transitions in electric fields from impurity ground states to states in the Mott-Hubbard gap.     

Anomalous Cs I 5d-5⨍ lineshape in a non-debye plasma

Laser-induced cesium plasmas were diagnosed by emission spectroscopy, yielding electron densities in the range N_e = 10¹⁶?5 × 10¹⁷ cm^-3 and electron temperatures in the range T_e = 0.2-1 eV. The experimental lineshapes for T_e = 0.5 eV were found to be in good agreement with theory. For the more strongly coupled plasmas at N_e = 1-2 × 10¹⁶ cm^-3 and T_e = 0.2 eV, however, the Cs I 5d-5? lineshape was more asymmetric than predicted.     

High-resolution Fourier spectrometry of 14N2 and 15N2 infrared emission spectrum: Extensive analysis of the W3Δu - B3Πg system

The infrared spectrum of the nitrogen molecule, excited in a microwave discharge, has been recorded in high resolution by Fourier spectrometry in the range 2500–15 000 cm^?1. The precision of the measurements is estimated to be about 0.003 cm^?1. We have analyzed 19 bands of the W³Δ_u-B³Π_g system of ¹⁴N₂, with 0 ≤ v′ ≤ 7, and three bands of ¹⁵N₂ lying between 2500 and 5900 cm^?1. The molecular constants of the ³Δ_u and B³Π_g states have been determined by direct approach using an iterative nonlinear least-squares procedure. It has proved convenient to describe the levels of W³Δ_u state in a case a basis although in fact they approximate those of Hund's case b. Derived values of equilibrium constants of W³Δ_u are, in cm^?1: T_e = 8875.3347 (with origin taken in A, ³Σ_u⁺v = 0 level); ω_e = 1506.4859; ω_eχ_e = 12.5469; B_e = 1.4702537; α_B = 0.0170389; D_e = 0.55958 × 10^?5. RKR potential energy curves for the two states are constructed, and the Franck-Condon factors calculated for the W-B system.     

Influence of Na-related defects on ArF laser absorption in CaF2

ArF laser pulse transmission through commercial high purity CaF₂ is determined by measuring the energy of each pulse before and behind the sample up to an incident fluence H of 10 mJ/cm². The steady state transmission of ArF laser pulses decreases with increasing fluence. The related absorption coefficients α ^st(H) are proportional to H and rationalized by effective 1- and 2-photon absorption coefficients 2.4×10^?4 cm^?1≤α ^eff≤16.8×10^?4 cm^?1 and 1.7×10^?9 cm?W^?1≤β ^eff≤9.3×10^?9 cm?W^?1, respectively. The α ^eff and β ^eff values increase with the Na content of the CaF₂ samples as identified by the fluorescence of Na-related M _Na centers at 740 nm. This relation is simulated by a rate equation model describing the ArF laser induced M _Na generation in the dark periods between the laser pulses and their annealing during laser irradiation. M _Na generation starts with intrinsic 2-photon absorption in CaF₂, yielding self-trapped excitons (STE). These pairs of F and H centers move upon thermal activation and the F centers combine with F _Na to form M _Na centers. M _Na annealing occurs by its photo dissociation into a pair of F and F _Na centers.