Electron Capture Cross Sections Research Articles

Reassessing iron–gallium recombination activity in silicon

In this work, we present a comprehensive re-evaluation of the iron–gallium (FeGa) recombination parameters in silicon using injection-dependent lifetime spectroscopy (IDLS). Ga-doped silicon wafers (of varying resistivities) with precise concentrations of intentional iron contamination in the silicon wafer bulk, through ion implantation and distribution, were used. The presence of interstitial Fei and FeGa, and their lifetime-limiting effects in these silicon wafers, were confirmed through measuring the effective minority carrier lifetime changes during the conditions that are known to cause FeGa dissociation and association. The presence of Fe was also confirmed by deep-level transient spectroscopy. To ensure accurate IDLS analysis of the FeGa defect in silicon, a lifetime linearization scheme was employed to effectively filter out interference by other defects. Error analysis was employed to find the combination of defect parameters that best fit the experimental data and to ascertain the range of uncertainty associated with the IDLS best-fit results. The optimal fitting of the experimental IDLS by Shockley–Read–Hall statistics produced an electron capture cross section σn=2.3×10−14cm2, hole capture cross section σp=1.1×10−14cm2, and a trap energy level Et=EV+0.2−0.01+0.02eV for the FeGa defect in silicon. The extracted defect parameters are also verified by experimentally measuring the crossover point of Fei and FeGa lifetime curves.

Space charge region recombination in highly efficient silicon solar cells

The recombination rate in the space charge region (SCR) of a silicon-based barrier structure with a long Shockley–Reed–Hall lifetime is calculated theoretically by taking into account the concentration gradient of excess electron-hole pairs in the base region. Effects of the SCR lifetime and applied voltage on the structure ideality factor have been analyzed. The ideality factor is significantly reduced by the concentration gradient of electron-hole pairs. This mechanism provides an increase of the effective lifetime compared to the case when it is insignificant, which is realized at sufficiently low pair concentrations. The theoretical results have been shown to be in agreement with experimental data. A method of finding the experimental recombination rate in SCR in highly efficient silicon solar cells (SCs) has been proposed and implemented. It has been shown that at the high excess carrier concentration exceeding 1015 cm–3 the contribution to the SCR recombination velocity from the initial region of SCR that became neutral is significant. From a comparison of theory with experiment, the SCR lifetime and the ratio of the hole to the electron capture cross sections are determined for a number of silicon SCs. The effect of SCR recombination on the key characteristics of highly efficient silicon SCs, such as photoconversion efficiency and open-circuit voltage, has been evaluated. It has been shown that they depend not only on the charge carrier lifetime in SCR, but also on the ratio of hole to electron capture cross sections σp /σn. When σp /σn < 1, this effect is significantly strengthened, while in the opposite case σp /σn > 1 it is weakened. It has been ascertained that in a number of highly efficient silicon SCs, the distribution of the inverse lifetime in SCR is described by the Gaussian one. The effect described in the paper is also significant for silicon diodes with a thin base, p-i-n structures, and for silicon transistors with p-n junctions. In Appendix 2, the need to take into account the lifetime of non-radiative excitonic Auger recombination with participation of deep impurities in silicon is analyzed in detail. It has been shown, in particular, that considering it enables to reconcile the theoretical and experimental dependences for the effective lifetime in the silicon bulk.

Highly conducting Al-doped zinc oxide electron transport layer for all-inorganic perovskite solar cells: An experimental and simulation study

The need for an excellent electron transport layer (ETL) material is immensely significant for higher conversion efficiency of perovskite solar cells (PSCs). This work centers on the exceptional performance achieved by the Al-doped ZnO (AZO) ETL with reference to undoped ZnO (ZnO). Both doped and undoped ETL materials were synthesized and characterized to determine their structural, morphological, and optical behavior. In this work, solar cell performance of two similar CsPbIBr2-based PSCs with different ETLs namely FTO/ZnO/CsPbIBr2/NiO (Cell #1) and FTO/AZO/CsPbIBr2/NiO (Cell #2) are investigated through numerical simulation method. The obtained characteristics affirms that Cell #2 offers sufficient better performance parameters (Jsc, Voc, FF, and η) against Cell #1 with respect to variation in CsPbIBr2 PVT, ETL and HTL thickness. The adverse effect on J-V characteristics caused by controllable introduction of defect density (Nt) in PVT layer is negligible for Cell #2 compared to its ZnO counterpart. Further, the contribution of AZO ETL layer on cell's performance is evaluated in terms of variation in respective ETL and HTL thickness. The investigation reveals that Cell #2 offers a desirable η of 19.46% at electron capture cross section of 2 × 10−15 cm2 while Cell #1 delivers only 12.48%.

Measurements of absolute electron capture cross sections in He2+–He and Ne8+–O2, N2, CH4 collisions

Measurements of absolute electron capture cross sections in He2+–He and Ne8+–O2, N2, CH4 collisions

Investigation of a minority carrier trap in a NiO/β-Ga2O3 p–n heterojunction via deep-level transient spectroscopy

The properties of a minority carrier (hole) trap in β-Ga2O3 have been explicitly investigated using a NiO/β-Ga2O3 p–n heterojunction. Via deep-level transient spectroscopy, the activation energy for emission (E emi) and the hole capture cross section (σp ) were derived to be 0.10 eV and 2.48 × 10−15 cm2, respectively. Temperature-enhanced capture and emission kinetics were revealed by the decrease in the capture time constant (τc ) and emission time constant (τe ). Moreover, it was determined that the emission process of the minority carrier trap is independent of the electric field. Taking carrier recombination into account, a corrected trap concentration (N Ta) of 2.73 × 1015 cm−3 was extracted, together with an electron capture cross section (σn ) of 1.42 × 10−18 cm2. This study provides a foundation for the comprehension of trap properties in β-Ga2O3, which is crucial for overcoming self-trapped hole effects when obtaining p-type β-Ga2O3 materials and performance enhancement of β-Ga2O3-based power devices.

Study of single electron capture in O6+ + He collisions

Research on electron capture (EC) process are undoubtedly helpful for maturing theoretical models on ion-induced collision especially for low-energy region. In this work, a two-active-electron semiclassical asymptotic-state close-coupling method was used to calculate the total and l-solved state-selective single EC cross sections of O6+ + He collisions in the energy range of 0.3–100 keV u−1, accompanied with experimental measurements in the energy range of 2.63–37.5 keV u−1 with an uncertainty of 11% in good agreement. Above 4.5 keV u−1, the state-selective cross section of n = 5 was reported experimentally for the first time. Calculations with multiple theoretical methods were gathered and compared with present calculations. The importance of two-active-electrons correlation and large basis sets in theoretical calculations was found, and discrepancies between previous theoretical and experimental results can be explained by the present results.

Calculation of Ionization, Excitation and Electron Capture Cross Sections for Be4+ + H(2s,2p) Collisions.

A computational study of Be4+ + H(2s,2p) collisions has been carried out employing the Classical Trajectory Monte Carlo (CTMC) method for the impact energy range from 20 keV/u to 1000 keV/u. The integral n partial cross sections for H(n) excitation and Be3+(n) electron capture and, the total ionization and electron capture cross sections are calculated and compared to recent semiclassical results. A general good agreement is observed for the n partial and total electron capture and ionization cross sections. The comparative study of the three inelastic processes show no significant differences between both excited targets.

Electron capture and ionisation in He^{2+} collisions with H_2

State-selective non-dissociative electron capture and ionisation cross sections are calculated for collisions between bare helium-ions and molecular hydrogen. The two-centre wave-packet convergent close-coupling approach is used and the hydrogen molecule is represented as an effective one-electron target. For the electron-capture cross section, our results are in good agreement with experimental measurements at energies above 100 keV/u. However, near the peak of the cross section, they are larger than the experimental data. The total ionisation cross section is also in good agreement with experiment, particularly at low and high energies. The results for the state-selective electron-capture cross section are generally in good agreement with the limited experimental measurements. However, we find that our results appear to consistently overestimate the experimental data for electron capture into the s states at intermediate energies. The present results are the first calculations capable of producing electron capture and ionisation cross sections over a wide incident energy range within a single unified theoretical framework.Graphical

Energy concepts involved in MOS characterization

Starting from a quantum statistical reasoning, it is demonstrated that entropy properties of silicon/silicon dioxide interface electron traps may have a strong influence on measured distributions of interface states, depending on measurement method used. For methods, where the Fermi-level is used as a probe to define an energy position, the scale is based on free energy. On the other hand, methods based on thermal activation of electrons give the distribution on an enthalpy scale. It is shown that measured interface state distributions are influenced by the distribution of entropy, and that common features of measured energy distributions may be influenced by entropy variations. These results are used to interpret experimental data on the energy distribution of electron capture cross sections with an exponential increase followed by a more or less constant value as the energy distance of the traps from the conduction band edge increases. Such a relation is shown to be consistent with a situation where the emission and capture processes of electrons obey the Meyer-Neldel rule.

Cross sections in He+ + H collisions for the energy region 1–100 keV u−1

We have calculated the cross sections for the elastic, excitation, electron capture, and ionization processes in He+ + H collision using a semiclassical atomic orbital close-coupling method within two-electron treatment. The calculated data are compared with those of the experiments and previous theoretical calculations. The excitation cross sections to H(n = 2) states are in good agreements with the measurements of Geddes et al. The Balmer-alpha emission cross section of H is about half the size of the experimental data of Donnelly et al. The electron capture cross section is close to the experimental data of Lockwood et al and Olson et al. The ionization cross section is in accord with the experimental data of Hsu et al.

Time-Dependent Density-Functional Theory for Determining the Electron-Capture Cross Section for Protons Impacting on Atoms and Molecules.

The use of the Time-Dependent Density-Functional Theory (TDDFT) has increased in the atomic collision field. Calculating the electron-capture cross section (ECCS) for protons is an important question in hadrontherapy and plasma physics, among other areas. In previous studies, it was shown that the approach based on the Local Density Approximation (LDA) fails in the 1-50 keV region, requiring the use of the Optimized Effective Potential (OEP) method. In this work, the ECCS values for 1-50 keV protons impacting on isolated hydrogen, carbon, nitrogen, oxygen, and nitrogenous atoms were determined using the TDDFT. It is shown that adding the Self Interaction Correction to the LDA (LDA-Sic) allows obtaining results close to those provided by the OEP and experiments, with the advantage that the LDA-Sic consumes less computational time. In addition, it was demonstrated that it is imperative to include the spin correction for the specific helium and oxygen cases, in order to get good results for the ECCS using the TDDFT. Theoretical results obtained in this work show excellent agreement with experimental values.

Wave-packet continuum discretization approach to He2+−He collisions

The two-center wave-packet convergent close-coupling method is generalized to multiply charged ion collisions with helium and applied to the ${\mathrm{He}}^{2+}\text{\ensuremath{-}}\mathrm{He}$ scattering problem. The approach is applicable in a wide range of collision energies including low and intermediate energies, where coupling between various reaction channels and electron exchange between the fragments in the rearrangement channel are important. The target structure is treated using the configuration-interaction method within the frozen-core approximation, where one of the electrons of the target is assumed to stay in the ground state throughout the collision. This accounts for the indistinguishability and the correlations between the electrons of the target. We also use a simpler alternative method that is based on an effective one-electron target description that neglects the electron-electron correlations. In both methods, the continuum of the target atom and the hydrogenlike atom formed after electron capture by the projectile is discretized using the wave-packet approach. We present cross sections for total and state-selective electron capture, excitation, and single ionization of the target. The results are provided for the incident energies from 10 keV/u to 5 MeV/u, where one-electron processes are expected to dominate. Particular attention is focused on the intermediate-energy region where substantial deviations between various theoretical results are found. However, overall, the present results are in good agreement with experimental data and other calculations, where available. We demonstrate that both effective single-electron and two-electron methods can provide a realistic picture of all single-electron scattering processes taking place in ${\mathrm{He}}^{2+}\text{\ensuremath{-}}\mathrm{He}$ collisions in terms of the total cross sections. This creates a reliable platform for modeling differential scattering and ionization in this four-body system.

Electron Capture and Ionisation in Collisions of Ne10+ and Li3+ with Atomic Hydrogen

The two-center wave-packet convergent close-coupling method has been applied to model the processes of electron capture and ionisation in collisions of fully stripped neon and lithium ions with atomic hydrogen at projectile energies from 1 keV/u to 1 MeV/u. For the Ne10+ projectile, the resulting total electron-capture cross section lies between the two sets of experimental results available for system, which differ from each other significantly. For Li3+, our total electron-capture cross section agrees with the available experimental measurements by Shah et al. [J. Phys. B: At. Mol. Opt. Phys 11, L233 (1978)] and Seim et al. [J. Phys. B: At. Mol. Opt. Phys 14, 3475 (1981)], particularly at low and high energies. We also get good agreement with the existing theoretical works, particularly the atomic- and molecular-orbital close-coupling calculations. Our total ionisation cross section overestimates the experimental data by Shah et al. [J. Phys. B: At. Mol. Opt. Phys 15, 413 (1982)] at the peak, however we get good agreement with the other existing theoretical calculations at low and high energies.

Clarifying the atomic origin of electron killers in β-Ga2O3 from the first-principles study of electron capture rates

The emerging wide bandgap semiconductor -Ga2O3 has attracted great interest due to its promising applications for high-power electronic devices and solar-blind ultraviolet photodetectors. Deep-level defects in -Ga2O3 have been intensively studied towards improving device performance. Deep-level signatures E 1, E 2, and E 3 with energy positions of 0.55–0.63, 0.74–0.81, and 1.01–1.10 eV below the conduction band minimum have frequently been observed and extensively investigated, but their atomic origins are still under debate. In this work, we attempt to clarify these deep-level signatures from the comparison of theoretically predicted electron capture cross-sections of suggested candidates, Ti and Fe substituting Ga on a tetrahedral site (TiGaI and FeGaI) and an octahedral site (TiGaII and FeGaII), to experimentally measured results. The first-principles approach predicted electron capture cross-sections of TiGaI and TiGaII defects are 8.56 × 10–14 and 2.97 × 10–13 cm2, in good agreement with the experimental values of E 1 and E 3 centers, respectively. We, therefore, confirmed that E 1 and E 3 centers are indeed associated with TiGaI and TiGaII defects, respectively. Whereas the predicted electron capture cross-sections of FeGa defect are two orders of magnitude larger than the experimental value of the E 2, indicating E 2 may have other origins like CGa and Gai, rather than common believed FeGa.

Prediction of charge-changing cross sections of low-charged 88Sr, 138Ba and 142Nd ions in a He-gas target at collision energies 50 eV/u–10 GeV/u

Electron-loss (EL) and electron-capture (EC) cross sections of neutral and low-charged heavy Srq+, Baq+ and Ndq+ ions with charges q = 0, 1 and 2 in collisions with He atoms are predicted in the energy range E = 50 eV/u–10 GeV/u. Experimental data on EL and EC cross sections of these particles colliding with He atoms are practically absent. At relatively low energies E = 8–30 keV, EL cross sections σ12 of Sr1+, Ba1+ and Nd1+ ions are predicted from new experimental equilibrium charge-state fractions F1 and F2 and calculated EC cross sections. Predicted value for Ba1+ ions, σ12=6.8⋅10−18cm2, is in a good agreement with the one available experimental point σ12exp=5.7⋅10−18cm2 at E = 20 keV (Fedorenko, 1954). Calculations of EL and EC cross sections are performed by available computer codes shortly described in the paper. Theoretically estimated neutral-atom fractions F0 are found much smaller than the measured F1, F2, and F3 charge-state fractions.

Thermal-annealing behavior of in-core neutron-irradiated epitaxial 4H[sbnd]SiC

The effect of thermal annealing on defect recovery of in-core neutron-irradiated 4HSiC was investigated. Au/SiC Schottky diodes were manufactured using a 4HSiC epitaxial wafer that was neutron-irradiated at the HANARO research reactor. The electrical characteristics of their epitaxial layers were analyzed under various conditions, including different neutron fluences (1.3 × 1017 and 2.7 × 1017 neutrons/cm2) and annealing times (up to 2 h at 1700 °C). Capacity–voltage measurements showed high carrier compensation in the neutron-irradiated samples and a recovery tendency that increased with annealing time. The carrier density could be recovered up to 77% of the bare sample. Deep-level-transient spectroscopy revealed intrinsic defects of 4HSiC with energy levels 0.47 and 0.68 eV below the conduction-band edge, which were significantly increased by in-core neutron irradiation. A previously unknown defect with a high electron-capture cross-section was discovered at 0.36 eV below the conduction-band edge. All defect concentrations decreased with 1700 °C annealing; the decrease was faster when the defect level was shallow.

Electron Capture on Nuclei in Stellar Environment

The stellar electron capture on nuclei is an essential, semi-leptonic process that is especially significant in the central environment of core-collapse supernovae and in the explosive stellar nucleosynthesis. In this article, on the basis of the original (absolute) electron-capture cross-sections under laboratory conditions that we computed in our previous work for a set of medium-weight nuclear isotopes, we extend this study and evaluate folded e−-capture rates in the stellar environment. With this aim, we assume that the parent nuclei and the projectile electrons interact when they are in the deep stellar interior during the late stages of the evolution of massive stars. Under these conditions (high matter densities and high temperatures of the pre-supernova and core-collapse supernova phases), we choose two categories of nuclei; the first includes the 48Ti and 56Fe isotopes that have A<65 and belong to the iron group of nuclei, and the second includes the heavier and more neutron-rich isotopes 66Zn and 90Zr (with A>65). In the former, the electron capture takes place mostly during the pre-supernova stage, while the latter occurs during the core-collapse supernova phase. A comparison with previous calculations, which were obtained by using various microscopic nuclear models employed for single-charge exchange nuclear reactions, is also included.

Comparing different charge-state models with experimental data of ion beams penetrating fully and partially ionized plasmas

In the present work, we have conducted a study to investigate the validity of three different charge-state models of ion beams penetrating plasma targets through a comparison with a total of five experiments from the literature. We have applied two alternative theoretical approaches. On the one hand, we have used a further extension of our cross-sectional model (CSM) code based on projectile electron loss and capture cross sections (rate equations) that was developed previously [Morales et al., Phys. Plasmas 24, 042703 (2017); R. Morales, Ph.D. thesis (Universidad de Castilla-La Mancha, 2019)]. On the other hand, we also used two charge-state models based on a semi-empirical formalism adapted to the plasma case: the Kreussler model [Kreussler et al., Phys. Rev. B 23, 82 (1981)] and the Gus'kov model [Guskov et al., Plasma Phys. Rep. 35, 709 (2009)]. Specifically, we present the predictions and the interpretation of the charge state of light to heavier ions at high, intermediate, and low velocities in Z-pinch and laser-produced partially and fully ionized plasmas. We are showing that experimental data support our new CSM code based on the cross-sectional formalism. In contrast, the framework based on semi-empirical formulas is less accurate for a precise charge-state prediction, but it can be applied for a reasonable stopping power calculation. Overall, results denote that the Gus'kov model is better suited to stopping power calculations at low projectile velocities and the Kreussler model fits better the energy loss data at intermediate velocities. Additionally, we propose a simple non-equilibrium charge model, derived from the semi-empirical framework, as a function of the ion path and equilibrium charge state.

A theoretical study of fragmentation dynamics of water dimer by proton impact

To investigate the collision processes of proton with the water dimer (H2O)2 at 50 eV, the time-dependent density functional theory coupled with molecular dynamics nonadiabatically is applied. Six specific collision orientations with various impact parameters are considered. The reaction channels, the mass distribution and the fragmentation mass spectrum are explored. Among all launched samples, the probability of the channel of non-charge transfer scattering and charge transfer scattering is about 80%, hinting that the probability of fragmentation is about 20%. The reaction channel of proton exchange process 2 is taken as an example to exhibit the detailed microscopic dynamics of the collision process by inspecting the positions, the respective distance, the number of loss of electrons and the evolution of the electron density. The study of the mass distribution and the fragmentation mass spectrum shows that among all possible fragments, the fragment with mass 36 has the highest relative abundance of 65%. The relative abundances of fragments with masses 1, 35, and 34 are 20%, 13%, and 1.5%, respectively. For the total electron capture cross section, the present calculations agree with the available measurements and calculations over the energy range from 50 eV to 12 keV.

Charge exchange in collisions of 1–100-keV Sn3+ ions with H2 and D2

Absolute cross sections for single electron capture by ${\mathrm{Sn}}^{3+}$ colliding with ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ have been measured and calculated in the energy range of 1--100 keV. The cross sections are determined by measuring the change in ion beam current with varying target density and by measuring the yields of charged target fragments by means of a time-of-flight spectrometer. The results for ${\mathrm{D}}_{2}$ show good agreement with our seven-state semiclassical calculations, while for ${\mathrm{H}}_{2}$ the experimental results increase more strongly than the calculations toward lower energies. This discrepancy is attributed to vibrational effects, not included in the calculations, that lead to the breakdown of the Franck-Condon approximation.