Electron Capture Cross Sections Research Articles

Importance of minority carrier response in accurate characterization of Ge metal-insulator-semiconductor interface traps

The ac signal response of majority and minority carriers at interface traps has been systematically investigated for Ge metal-insulator-semiconductor (MIS) interfaces by the conductance method. The conventional model including only the majority carrier response is compared with a newly proposed model, which includes the majority and minority carrier responses at interface traps. It is found that the conventional model cannot represent the measured conductance-frequency (G-F) curves of a Ge MIS capacitor near room temperature. It is revealed, on the other hand, that the modified model including the both types of carrier responses can accurately represent the measured G-F curves under the bias conditions from depletion to weak inversion even near room temperature. This demonstrates that the analysis including the both types of carriers responses is quite important in applying the conductance method to the Ge MIS capacitors near room temperature and that the model gives the accurate interface properties. As a result, the electron capture cross section of the Ge MIS capacitors is found to be almost independent of energy as is the case of a Si metal-oxide-semiconductor interface, suggesting that the defect structure similar to the Si MOS interface could be formed at the Ge MIS interface.

Temperature dependent carrier lifetime studies on Ti-doped multicrystalline silicon

Carrier lifetime measurements were performed on deliberately Ti-doped multicrystalline silicon wafers using a temperature controlled photoconductance device. The dominant recombination center was found to be the double-donor level associated with interstitial titanium. The interstitial Ti concentrations in multicrystalline silicon wafers were determined by measuring the Shockley–Read–Hall time constant for holes and using the known values of the thermal velocity and capture cross section for holes of the double-donor level at different temperatures. The measured values of the Ti concentration were then used to determine the electron capture cross section of the double-donor level over the temperature range of 140–270 °C via the measured values of the Shockley–Read–Hall time constant for electrons and the known thermal velocity. Multiphonon emission was found to be the most likely capture mechanism for this temperature range for electron capture into the double-donor level of Ti in silicon. The effective segregation coefficient for Ti was estimated by fitting Scheil’s equation to the measured values of the Ti concentrations and their respective vertical positions in the ingot. If all Ti were present as the interstitial double-donor, a lower limit of 1.8×10−6 can be ascribed to the segregation coefficient, which is very close to the equilibrium value.

Impact of Minorty Carrier Response on Characterization of Ge MIS Interface Traps

The response of majority and minority carriers with interface traps have been systematically investigated for Ge MIS interfaces with various interface layers by the conductance method based on the conventional model including the only majority carrier response and a newly-proposed model including the both carrier responses with interface traps. The analysis by using the conventional model leads to the inappropriate results of the Ge MIS interface properties near room temperature. On the other hand, the proposed model can accurately characterize ones. As a result, the electron capture cross-sections hardly depend on the energy in all samples as similar with those of Si MOS interface traps. This result indicates that the similar defects to a Si MOS interface are formed at the Ge MIS interfaces. Furthermore, the magnitudes of the cross-sections for each sample depend on the oxygen or nitrogen contents of the interface layers, suggesting that the different defect structures exist.

Dynamics of He2+ + He+(1s) and He2+ + He+(2s) excitation and electron-capture processes with screened Coulomb interaction

Collision dynamics of He2+ + He+(1s) and He2+ + He+(2s) excitation and electron capture in hot, dense plasmas is studied by the two-centre atomic orbital close-coupling method in the energy range 2–100 keV/u. The screening of the Coulomb interaction due to the plasma effects introduces significant changes in electronic bound state wavefunctions and energies (including lifting of Coulomb degeneracy), coupling matrix elements, and the number of open reaction channels, thus affecting the entire collision dynamics of the system. With increasing interaction screening, the total electron-capture cross sections for the considered collision systems increase with respect to those of the unscreened case in the lower part of the considered energy range, whereas in its high-energy part they show the opposite behaviour. The excitation cross sections generally decrease with increasing screening but show an oscillatory behaviour almost in the entire energy range considered. The cross section for the He2+ + He+(2s) → He2+ + He+(2p) excitation is several orders of magnitude larger than the cross sections for all other transitions and is highly sensitive to the strength of the interaction screening. This strongly affects the intensity and other spectral properties of the associated He+ Ly-α radiation.

Dynamics ofO8++Helectron capture in Debye plasmas

The electron capture in ${\text{O}}^{8+}\ensuremath{-}\text{H}$ collisions is studied by the two-center atomic-orbital close-coupling method when the interactions of charged particles are screened and have a Yukawa form. Atomic orbitals and eigenenergies of $n\ensuremath{\le}7$ states on ${\text{O}}^{7+}$ and $n\ensuremath{\le}2$ states on H are calculated as a function of the interaction screening parameter and used in the atomic-orbital close-coupling dynamics scheme to calculate the electron capture cross sections in the energy range of 0.2--50 keV/u. It is shown that the degree of interaction screening determines the reduction in electron binding energies, the number of open electron capture channels, and the strength of the exchange couplings, thus affecting the entire collision dynamics and the magnitude and energy behavior of state-selective cross sections. The changes in electron binding energies and capture cross sections when the interaction screening varies introduce dramatic changes in the radiation spectrum of ${\text{O}}^{7+}(nl)$ capture states with respect to the unscreened interaction case. The state-selective electron capture cross sections in this collision system, as well as the intensities of a number of charge exchange spectral lines, for a number of representative screening parameter values are presented and discussed.

Electron capture from excited hydrogen atoms by highly charged beryllium and carbon ions

The cross sections for electron capture in collisions of bare and helium-like ions of Be and C with excited H atoms (n = 2) have been calculated by a molecular-state close-coupling method in a collision energy range of 60 eV/amu-6 keV/amu. Calculated results show that these cross sections are remarkably larger than those for collisions with ground-state H atoms. For example, for collisions of Be2+, Be4+, C4+, and C6+ ions with H(2s) atoms at ∼1 keV/amu, the cross sections are 190 _ 10–16 cm2, 610 _ 10–16 cm2, 920 _ 10–16 cm2, and 720 _ 10–16 cm2, respectively. In contrast, the cross sections for collisions with ground-state H atoms are 25 _ 10–16 cm2, 35 _ 10–16 cm2, 30 _ 10–16 cm2, and 40 _ 10–16 cm2, respectively.

Analysis of the relationship between the electron-capture and electron-loss cross sections for carbon ions

The electron-loss cross sections σi, i + 1 and the electron-capture cross sections σi, i − 1 for carbon ions with energies of 35–330 keV/nucleon in hydrogen and neon are determined from experimental data. It is demonstrated that, for particle energies which satisfy the condition σi, i + 1 = σi, i − 1 or σi, i − 1 = σi − 1, i, the average equilibrium ion charge can be evaluated without solving the system of differential equations for charge exchange. The dependence of the average equilibrium ion charge on the ion energy is investigated for carbon ions.

Cross sections for single electron capture in collisions of N2+ with He at low energies

The absolute cross sections of single electron capture during the collision of N2+ with He have been measured over the energy range 0.1-300 eV/u. From the plot showing the dependence of cross sections on energy, the following three remarkable observations can be made: (1) the cross sections exhibit an oscillatory structure below 1eV/u, (2) a bend in the cross sections appears at approximately 1 eV/u and (3) there is a dip in the cross sections at approximately 70 eV/u. The formation of an oscillatory structure is attributed to the glory effect. The bend in the cross sections occurs owing to the attractive potential part of a l2n state of quasimolecule NHe2+. The dip in the cross sections appears as a result of opening a new reaction path above 70eV/u. The glory effect can be observed for the first time on a total cross section even for slow ion-neutral collisions. The objective of this study is to explore the possibilities of providing a detailed explanation of energy dependence measurements in order to study reaction dynamics for a charge changing process.

Dissociative and non-dissociative charge-changing processes in 1.0-2.0 MeV/u O5+ + O2 collisions

In the present work molecular ionization and dissociation correlated with projectile single electron capture and loss is investigated as a function of energy for O5+ + O2 collisions. Coincidence recoil-ion spectra as well as total projectile charge-changing yields were measured for projectile energies of 1.0, 1.5, and 2.0 MeV/u. Charge states for dissociative and non-dissociative recoiling products of the target molecular oxygen were identified. Ratios of charged molecular fragment yields to single non-dissociative ionization yields as a function of projectile energy were determined as well as total cross sections for projectile single electron capture and loss.

Probing the mechanism of electron capture and electron transfer dissociation using tags with variable electron affinity.

Electron capture dissociation (ECD) and electron transfer dissociation (ETD) of doubly protonated electron affinity (EA)-tuned peptides were studied to further illuminate the mechanism of these processes. The model peptide FQpSEEQQQTEDELQDK, containing a phosphoserine residue, was converted to EA-tuned peptides via beta-elimination and Michael addition of various thiol compounds. These include propanyl, benzyl, 4-cyanobenzyl, perfluorobenzyl, 3,5-dicyanobenzyl, 3-nitrobenzyl, and 3,5-dinitrobenzyl structural moieties, having a range of EA from -1.15 to +1.65 eV, excluding the propanyl group. Typical ECD or ETD backbone fragmentations are completely inhibited in peptides with substituent tags having EA over 1.00 eV, which are referred to as electron predators in this work. Nearly identical rates of electron capture by the dications substituted by the benzyl (EA = -1.15 eV) and 3-nitrobenzyl (EA = 1.00 eV) moieties are observed, which indicates the similarity of electron capture cross sections for the two derivatized peptides. This observation leads to the inference that electron capture kinetics are governed by the long-range electron-dication interaction and are not affected by side chain derivatives with positive EA. Once an electron is captured to high-n Rydberg states, however, through-space or through-bond electron transfer to the EA-tuning tags or low-n Rydberg states via potential curve crossing occurs in competition with transfer to the amide pi* orbital. The energetics of these processes are evaluated using time-dependent density functional theory with a series of reduced model systems. The intramolecular electron transfer process is modulated by structure-dependent hydrogen bonds and is heavily affected by the presence and type of electron-withdrawing groups in the EA-tuning tag. The anion radicals formed by electron predators have high proton affinities (approximately 1400 kJ/mol for the 3-nitrobenzyl anion radical) in comparison to other basic sites in the model peptide dication, facilitating exothermic proton transfer from one of the two sites of protonation. This interrupts the normal sequence of events in ECD or ETD, leading to backbone fragmentation by forming a stable radical intermediate. The implications which these results have for previously proposed ECD and ETD mechanisms are discussed.

Defects and instabilities in Hf-dielectric/SiON stacks (Invited Paper)

In this work, a review on the recent progress in understanding defects and instabilities in Hf-dielectric/SiON stacks will be given for both nMOSFETs and pMOSFETs. The key issues addressed for nMOSFETs include the capture cross section of electron traps, their location and justification of the model used. For pMOSFETs, a framework will be proposed for the defects and then used to interpret the anomalous NBTI kinetics. The dominant dielectric layer for positive charging will be identified. Wherever possible, the classical SiO 2 will be used as a benchmark and the similarity and difference between the stack and SiO 2 will be highlighted. It will be shown that the stack behaves like a degraded SiO 2.

Thermal effects on electron capture for neutron-rich nuclei

Thermal effects on allowed and first-forbidden proton-neutron transitions in neutron-rich nuclei are studied with the formalism of the thermofield dynamics. The p → n transition strength distributions as well as an electron capture cross section for the parent nucleus 76Ge are calculated at different temperatures with the Hamiltonian of the quasiparticle-phonon nuclear model.

Investigation of Fired and Non-fired Si-SiNx Interface Properties by Deep-level Transient Spectroscopy measurements

AbstractIn this paper, fired and non-fired direct PECVD deposited Si-SiNx interface properties with and without NH3 pretreatment on both n- and p-type mono-crystalline silicon samples were investigated with deep-level transient spectroscopy (DLTS) measurements. A and B defect states are identified at the Si-SiNx interface. Energy-dependent electron and hole capture cross sections were measured by small-pulse DLTS. Fired samples with NH3 pretreatment show the lowest DLTS signals, which suggests the lowest overall Dit. The combination of NH3 pretreatment and firing is also suggested for application in the solar cell fabrication.

ERCS08: A FORTRAN program equipped with a Windows graphics user interface that calculates ECPSSR cross sections for the removal of atomic electrons

ERCS08 is a program for computing the atomic electron removal cross sections. It is written in FORTRAN in order to make it more portable and easier to customize by a large community of physicists, but it also comes with a separate windows graphics user interface control application ERCS08w that makes it easy to quickly prepare the input file, run the program, as well as view and analyze the output. The calculations are based on the ECPSSR theory for direct (Coulomb) ionization and non-radiative electron capture. With versatility in mind, the program allows for selective inclusion or exclusion of individual contributions to the cross sections from effects such as projectile energy loss, Coulomb deflection of the projectile, perturbation of electron's stationary state (polarization and binding), as well as relativity. This makes it straightforward to assess the importance of each effect in a given collision regime. The control application also makes it easy to setup for calculations in inverse kinematics (i.e. ionization of projectile ions by target atoms or ions). Program summary Program title: ERCS08 Catalogue identifier: AECU_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AECU_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 12 832 No. of bytes in distributed program, including test data, etc.: 318 420 Distribution format: tar.gz Programming language: Once the input file is prepared (using a text editor or ERCS08w), all the calculations are done in FORTRAN using double precision. Computer: see “Operating system” below Operating system: The main program (ERCS08) can run on any computer equipped with a FORTRAN compiler. Its pre-compiled executable file (supplied) runs under DOS or Windows. The supplied graphics user interface control application (ERCS08w) requires a Windows operating system. ERCS08w is designed to be used along with a text editor. Any editor can be used, including the one that comes with the operating system (for example, Edit for DOS or Notepad for Windows). Classification: 16.7, 16.8 Nature of problem: ECPSSR has become a typical tag word for a theory that goes beyond the standard plane wave Born approximation (PWBA) in order to predict the cross sections for direct (Coulomb) ionization of atomic electrons by projectile ions, taking into account the energy loss (E) and Coulomb deflection (C) of the projectile, as well as the perturbed stationary state (PSS) and relativistic nature (R) of the target electron. Its treatment of non-radiative electron capture to the projectile goes beyond the Oppenheimer–Brinkman–Kramers approximation (OBK) to include the effects of C, PSS, and R. PSS is described in terms of increased target electron binding (B) due to the presence of the projectile in the vicinity of the target nucleus, and (for direct ionization only) polarization of the target electron cloud (P) while projectile is outside the electron's shell radius. Several modifications of the theory have been recently suggested or endorsed by one of its authors (Lapicki). These modifications are sometimes explicit in the tag word (for example, eCPSSR, eCUSR, ReCPSShsR, etc.) A cross section for the ionization of a target electron is assumed to equal the sum of the cross sections for direct ionization (DI) and electron capture (EC). Solution method: The calculations are based on the ECPSSR theory for direct (Coulomb) ionization and non-radiative electron capture. With versatility in mind, the program allows for selective inclusion or exclusion of individual contributions to the cross sections from effects such as projectile energy loss, Coulomb deflection of the projectile, perturbation of electron's stationary state (polarization and binding), as well as relativity. This makes it straightforward to assess the importance of each effect in a given collision regime. The control application also makes it easy to setup for calculations in inverse kinematics (i.e. ionization of projectile ions by target atoms or ions). Restrictions: The program is restricted to the ionization of K, L, and M electrons. The theory is non-relativistic, which effectively limits its applicability to projectile energies up to about 50 MeV/amu. However, the theory is extended to apply to relativistic light projectiles. Radiative electron capture is not taken into account, since its contribution is found to be negligible in the collision regimes covered by the ECPSSR theory. Unusual features: Windows graphics user interface along with a FORTRAN code for calculations, selective inclusion or exclusion of specific corrections, inclusion of the extension to relativistic light projectiles, inclusion of non-radiative electron capture. Running time: Running the program using the input data provided with the distribution only takes a few seconds.

Double capture cross sections inp−Arcollisions

$p\text{\ensuremath{-}}\mathrm{Ar}$ collisions are investigated theoretically and experimentally at impact energies in the keV regime. Total cross sections for double electron capture of $p$ on Ar are calculated by an independent-particle method in the impact energy range $3--100\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$. We have measured the absolute differential and total cross sections for double electron capture for $1.0--5.0\text{\ensuremath{-}}\mathrm{keV}$ $p\text{\ensuremath{-}}\mathrm{Ar}$ collisions. The absolute differential cross section (DCS) for all the collision energies considered shows a decreasing behavior with increasing angle, exhibiting an overall decrease of three orders of magnitude. The integrated DCS is found to be between the range of $0.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ and $4.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{2}$, displays an increasing behavior as a function of the incident energy, and merges with previous data at the high-energy side. The theoretical total cross sections reproduce the structures around $5\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ and $15\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ reported by other available measurements. The analysis of the capture into the $1{s}^{1}4{s}^{1}$ hydrogen-like configuration points in the direction of a common origin for these peaks.

Polarization effects on the cross-section of ion–atom collisions

Coupled-channel cross-sections for electron capture, ionization and electron loss due to polarization effects are calculated. The maximum impact parameter for electron escape is analyzed within the classical framework. The probabilities of ionization and capture are analyzed simultaneously by a semi-empirical method. Differing from the n-body classical trajectory Monte Carlo method, the condition for electron escape is determined by Coulomb forces related to the two nuclei. This method can be used to calculate coupled-channel cross-sections rather than single-channel ones in other methods. Therefore the calculated results can be compared with experimental data directly. In the low energy range, neglecting the ionization effect, the single-capture cross-sections of hydrogen atoms induced by various partially-stripped ions were calculated. In the high energy range, neglecting the capture effect on ionization, the pure-ionization cross-sections of neon atoms induced by Ne q + ( q = 4, 6, 8) and Ar q + ( q = 4, 6, 8, 10) at an incident energy E = 1.05 MeV/u were calculated. Good agreement was found between our calculation and experimental data in the literature. This method had been partially applied for intermediate energy successfully.

Electron Capture, Hydrogen Release, and Enhanced Gain Degradation in Linear Bipolar Devices

We present evidence that enhanced low-dose-rate sensitivity (ELDRS) in lateral and substrate pnp bipolar devices can occur because of the much lower probability for electron capture by protons in SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , as compared to mobile or trapped holes. New experimental results and a critical evaluation of previous work demonstrate that, at high dose rates and/or in oxides with low concentrations of hydrogen, electrons can more easily neutralize slowly diffusing or metastably trapped holes via annihilation (recombination) or compensation (offsetting trapping) before the holes can release H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> . In contrast, at low dose rates and/or in oxides with higher concentrations of hydrogen, which can react with and modify the structure of O-vacancy-related defects, it is more likely that holes can release H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> during transport. This is because the cross section for electron capture by H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> is several orders of magnitude smaller than the electron capture cross section for a slowly moving or metastably trapped hole. This enhanced proton release at low dose rates or in oxides with high hydrogen concentrations can lead to increased interface trap formation, which is the most common source of enhanced gain degradation in lateral and substrate pnp bipolar transistors.

Charge exchange of medium energy H and He ions emerging from solid surfaces

Charge exchange of medium energy H and He ions emerging from clean solid surfaces is studied extensively using a toroidal electrostatic analyzer with an excellent energy resolution. The charge distributions of He ions scattered from sub-monolayers near a surface are non-equilibrated, resulting in a surface peak even for poly-crystal solids. By solving simultaneous rate equations numerically, we derive electron capture and loss cross sections for Ni and Au surfaces. Based on a free electron gas model, non-equilibrated He+ fractions dependent on emerging angle reveals uniform electronic surfaces for metals and corrugated surfaces for Si and graphite with covalent bonds. It is also found that equilibrium charge fractions of H+ are independent of surface materials (Z2) and in contrast equilibrium He+ fractions depend pronouncedly on Z2. The data obtained are compared with semi-empirical formulas.

Collision-induced fragmentation cross sections ofCO2+on He: Experiment and theory

A combined experimental and theoretical study of the collision-induced dissociation of $\mathrm{C}\mathrm{O}_{2}{}^{+}$ ions colliding with He in the energy range of $1\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}9\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ has been carried out in this work. Total cross sections for the dissociation products ${\mathrm{O}}^{+}$, ${\mathrm{C}}^{+}$, and $\mathrm{C}{\mathrm{O}}^{+}$ are presented as a mean to investigate the collision dynamics of this molecular ion. A remarkable change on the dissociation dynamics is resolved at about $\ensuremath{\sim}4\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ collision energy. From the comparison of the measured cross sections to a theoretical treatment of the collision process using electron-nuclear dynamics, we infer that electronic multireference configurations are required in the dynamics at low collision energies. For the ${\mathrm{C}}^{+}$ dissociation product, the collision dynamics is fully described by theory with the possible isomerization of the $\mathrm{C}\mathrm{O}_{2}{}^{+}$ being discarded at these collision energies. As a consequence of the calibration procedure in the experimental method, double electron capture cross section for protons on argon are also reported in good agreement with other available experiments.

Quantum oscillatory screening effects on the charge capture process in quantum plasmas

The quantum oscillatory screening effects on the charge capture process are investigated in quantum plasmas. The Bohr–Lindhard formalism with the modified Debye–Hückel potential is employed for obtaining the electron capture radius and probability as functions of the quantum wave number, projectile energy and ion charge number. It is shown that the oscillatory screening effects suppress the electron capture cross section as well as the capture radius. It is also shown that the electron capture radius increases with decreasing quantum wave number. The oscillatory screening effects on the capture radius are found to increase with an increase of the quantum wave number and the ion charge number. In addition, the domain of the capture cross section is found to decrease due to the quantum oscillatory screening effects and also reduces with an increase of the quantum wave number.