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We characterized an intrinsic interface defect, called the "PbC center," formed at 4H-SiC(0001)/SiO2 interfaces by means of electron-spin-resonance (ESR) and electrically detected-magnetic-resonance (EDMR) spectroscopies. The formation of the PbC center was observed with a spin density of 3–4 × 1012 cm−2 after standard thermal oxidation. This center could be effectively removed by the NO post-oxidation-anneal (POA) process or ultra-high-temperature oxidation and could be passivated by H atoms via the H2 POA process. There was a clear correlation between the PbC center and field-effect mobility (μFE) of 4H-SiC(0001) metal–oxide–semiconductor field effect transistors (MOSFETs). The PbC center decreased μFE because this center acts as electron traps, reducing the free-carrier density in the inversion channel of 4H-SiC(0001) MOSFET. We also examined the counter doping effect of NO POA by introducing 15N impurities; however, the counter doping of 15N donors was not detectable by ESR (much lower than 2 × 1011 cm−2). Highly sensitive EDMR measurements revealed that the PbC center has two isotropic hyperfine (HF) interactions at 1.3 and 6.8 mT and suggested that its main 13C HF interaction should be larger than 14 mT. Based on the present experimental data, the origin of the PbC center was ascribed as a carbon-related interface defect that forms a C–H bond after hydrogen passivation. This feature is similar to that of the porous-PbC centers (carbon dangling-bond centers) found in porous-SiC/SiO2 systems. However, their HF signatures indicated that the PbC center at 4H-SiC(0001)/SiO2 interfaces and the porous-PbC centers in porous-SiC should be different centers associated with different wave functions. [ABSTRACT FROM AUTHOR]

We investigated a metal-oxide-semiconductor interface of dry-oxidized (000 1 ¯ ) 4H-SiC, which was known as the most electrically deteriorated SiC MOSFET, by electrically detected magnetic resonance (EDMR) and observed a signal with an isotropic g factor (2.0024) and magnetic-field angular dependent signal widths. Judging from the g factor, the signal comes from sp2-bonded carbon clusters. In addition, we found that the angular dependence of EDMR signal widths was caused by two-dimensional dipolar broadening with exchange interaction between electron spins. However, the density of electron spins or carbon clusters was 5.4 × 1013 cm−2, which was not high enough for exchange interaction. Therefore, we propose inhomogeneous distribution of carbon clusters in the interface. At the interface, π* peaks from sp2-bonded carbon atoms were detected by electron energy loss spectroscopy. Scanning the electron beams along the interface revealed uneven existence of the π* peaks, which also proved that the sp2-bonded carbon atoms were distributed inhomogeneously in the interface. In addition, we found the formation of sp2-bonded carbon clusters at 4H-SiC(000 1 ¯ )/SiO2 interfaces and interaction between π-conjugate electron spins on the carbon clusters by first principles calculation. Such carbon clusters generated electrically active states widely in the energy gap of 4H-SiC. The states result in the Fermi level pinning of the MOSFET. [ABSTRACT FROM AUTHOR]

Magnetic reconnection is a key fundamental process in collisionless plasmas, which converts magnetic energy to plasma kinetic energy. Past observation and simulation studies suggested that this process causes an efficient energy conversion through the formation and coalescence of multiple magnetic islands. In this study, based on a large-scale two-dimensional fully kinetic simulations of coalescing multiple islands with a moderate guide magnetic field, we first examined the spatial dimensions of the internal structures of the coalescing islands. The results show that the dimensions of the structures in the directions normal to and along the initial current sheet depend on the initial thickness of the current sheet and the number of coalescing islands. We then found that the horizontal dimension of the structures controls the evolution time scale of the island coalescence process. We further found that when the vertical dimension of the structures, which corresponds to the length of the reconnection X-line in the reconnection outflow direction at the merging point between the two coalescing islands, is sufficiently longer than the ion inertial length, reconnection in the merging current sheet can well mature and both ions and electrons can be effectively heated around the merging X-line. The obtained scaling predicts that such a strong heating by well-matured reconnection in the island coalescence process would be seen in various plasma environments, such as the Earth's magnetotail and solar flares. [ABSTRACT FROM AUTHOR]

At the Earth's low-latitude magnetopause, the Kelvin–Helmholtz instability (KHI), driven by the velocity shear between the magnetosheath and magnetosphere, has been frequently observed during northward interplanetary magnetic field (IMF) periods. However, the signatures of the KHI have been much less frequently observed during southward IMF periods, and how the KHI develops under southward IMF has been less explored. Here, we performed a series of realistic 2D and 3D fully kinetic simulations of a KH wave event observed by the Magnetospheric Multiscale (MMS) mission at the dusk-flank magnetopause during southward IMF on September 23, 2017. The simulations demonstrate that the primary KHI bends the magnetopause current layer and excites the Rayleigh–Taylor instability (RTI), leading to penetration of high-density arms into the magnetospheric side. This arm penetration disturbs the structures of the vortex layer and produces intermittent and irregular variations of the surface waves which significantly reduces the observational probability of the periodic KH waves. The simulations further demonstrate that in the non-linear growth phase of the primary KHI, the lower-hybrid drift instability (LHDI) is induced near the edge of the primary vortices and contributes to an efficient plasma mixing across the magnetopause. The signatures of the large-scale surface waves by the KHI/RTI and the small-scale fluctuations by the LHDI are reasonably consistent with the MMS observations. These results indicate that the multi-scale evolution of the magnetopause KH waves and the resulting plasma transport and mixing as seen in the simulations may occur during southward IMF. [ABSTRACT FROM AUTHOR]

We investigated interface defects formed on a-face and m-face 4H-SiC/SiO2 interfaces after interface nitridation by nitric oxide (NO) post-oxidation annealing (POA). Using electrically detected magnetic-resonance spectroscopy, we observed interface defects on these faces. The a- and m-face interface defects were found to be similar to a carbon-related interface defect (the PbC center) observed on the standard Si-face, but their amounts were significantly lower than those of the Si-face after the same NO POA. Such a reduction was correlated with a drastic increase in the field-effect mobility (80–90 cm2 V−1 s−1) of the a- and m-face metal-oxide-semiconductor field-effect transistors after NO POA. We also found that over-nitridation caused the formation of two types of nitrogen-related defects on the Si-face. These nitrogen-related defects resemble the K center (Si dangling-bond center) observed in Si3N4. [ABSTRACT FROM AUTHOR]

We identify a carbon dangling-bond center intrinsically formed at thermally oxidized 4H-SiC(0001)/SiO2 interfaces. Our electrically detected-magnetic-resonance spectroscopy and first-principles calculations demonstrate that this center, which we name "the PbC center," is formed at a carbon adatom on the 4H-SiC(0001) honeycomb-like structure. The PbC center (Si3≡C-, where "-" represents an unpaired electron) is determined to be a just carbon version of the famous Pb center (Si dangling-bond center, Si3≡Si-) at Si(111)/SiO2 interfaces because we found close similarities between their wave functions. The PbC center acts as one of the major interfacial traps in 4H-SiC(0001) metal-oxide-semiconductor field-effect transistors (MOSFETs), which decreases the free-carrier density and the field-effect mobility of 4H-SiC(0001) MOSFETs. The formation of the PbC centers has the role of reducing the oxidation-induced strain, similar to the case of the formation of the Pb centers. [ABSTRACT FROM AUTHOR]

We used electrically detected magnetic resonance to study the microscopic structure of ion-implantation-induced point defects that remained in large-scale Si integrated circuits (Si LSIs). Two types of defects were detected in the source/drain (n[sup +]-type) region of 0.25-μm-gate-length n-channel metal oxide semiconductor field-effect-transistors on LSIs: (i) a spin-1 Si dangling-bond (DB) pair in divacancy–oxygen complexes (DB–DB distance, R≈0.6 nm); and (ii) a series of larger Si vacancies involving distant Si DBs (R>=1.4 nm). These vacancy-type defects were much more thermally stable in Si LSIs than those in bulk Si crystals. We suggested two physical mechanisms for this enhanced stability: internal mechanical stress and oxygen incorporation in the active regions of LSIs. After examining the relationship between the defects and current–voltage characteristics, we concluded that these defects are distributed in the near-surface n[sup +]-type region close to the gate and that they are the source of the gate-induced drain leakage currents. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present electrically detected-magnetic-resonance (EDMR) identification of major and minor interface defects at wet-oxidized 4H-SiC(000 1 ¯ )/SiO2 interfaces for C-face 4H-SiC metal-oxide-semiconductor field-effect transistors. The major interface defects are identified as c-axial types of carbon-antisite-carbon-vacancy (CSiVC) defects. Their positive (+1) charge state generates a spin-1/2 EDMR center named "C-face defects" and behaves as an interfacial hole trap. This center is responsible for the effective hydrogen passivation of the C face. We also identify a minor type of interface defect at this interface called "P8 centers," which appear as spin-1 centers. Judging from their similarity to the P7 centers (divacancies, VSiVC) in SiC, they were assigned to be a sort of basal-type interfacial VSiVC defect. Since both the CSiVC and VSiVC defects are known as promising single photon sources (SPSs) in SiC, the wet oxidation of the C face will have good potential for developing SPSs embedded at SiC surfaces. [ABSTRACT FROM AUTHOR]

The development of decaying magnetosonic/whistler mode turbulence is investigated, employing a two-dimensional, fully kinetic, particle-in-cell simulation that covers scales at the end of the inertial range. The anisotropic wavenumber spectrum of magnetic fluctuations reaches electron kinetic scales through the forward cascade of the turbulence. The magnetic fluctuations have intermittency at scales shorter than the ion inertial length. The intermittent nature leads to a localized steepening of magnetic fluctuations which accelerates ions nonlinearly in the direction perpendicular to the background magnetic field. The non-thermal ions have the speed of several times faster than the ion thermal speed. The fully kinetic particle-in-cell simulation shows important implications for a fundamental understanding of the non-thermal ion production in magnetosonic/whistler mode turbulence. [ABSTRACT FROM AUTHOR]

We study an electron-spin-resonance (ESR) signal of carbon dangling-bond defects at 4H-SiC(0001)/SiO2 interfaces, which we call an “interface carbon defect.” The ESR signal is close to a c-axial type of the PbC centers (interfacial carbon dangling bonds) that have originally been found in porous-SiC/SiO2 interfaces. The interface carbon defects were always formed with an areal density of 3–4 × 1012 cm−2 after the standard dry oxidation of 4H-SiC(0001) surfaces. They act as electron traps and decrease the amount of free electrons in the channel region, consequently reducing the field-effect mobility of Si-face 4H-SiC MOSFETs. They were eliminated by optimum post-oxidation anneals (POAs) in either NO or POCl3 environment. Furthermore, POCl3 POAs at 1000 °C introduced a high density (1.7 × 1012 cm−2) of phosphorus donors into the channel region, increasing the free-carrier density as compared with the case of NO POAs. [ABSTRACT FROM AUTHOR]

We present single photon sources (SPSs) embedded in 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs). They are formed in the SiC/SiO2 interface regions of wet-oxidation C-face 4H-SiC MOSFETs and were not found in other C-face and Si-face MOSFETs. Their bright room-temperature photoluminescence (PL) was observed in the range from 550 to 750 nm and revealed variable multi-peak structures as well as variable peak shifts. We characterized a wide variety of their PL spectra as the inevitable variation of local atomic structures at the interface. Their polarization dependence indicates that they are formed at the SiC side of the interface. We also demonstrate that it is possible to switch on/off the SPSs by a bias voltage of the MOSFET. [ABSTRACT FROM AUTHOR]

A two-dimensional, fully kinetic, electromagnetic, particle-in-cell simulation in a magnetized collisionless plasma has been performed, demonstrating the generation of intermittent ion acoustic waves in finite-amplitude whistler-mode turbulence. The self-consistent simulation shows that ion/ion acoustic instability can be driven as a consequence of the nonlinear evolution of whistler-mode turbulence. The instability triggering the generation of ion acoustic waves occurs intermittently in several local regions. We propose that the nonlinear development of the phase-space density that drives kinetic instabilities must be analyzed with greater care if the dissipation of plasma turbulence is to be understood. [ABSTRACT FROM AUTHOR]

A simple point of view that non-zero Alfven ratio (residual energy) appears as a consequence of one-fluid modeling of uni-directional Alfven waves in a solar wind plasma is presented. Since relative speeds among ions are incorporated into the one-fluid model as a pressure anisotropy, the Alfven ratio can be finite due to the decrease in the phase velocity. It is shown that a proton beam component typically found in the solar wind plasma can contribute to generating non-zero Alfven ratio observed in the solar wind plasma. Local equilibrium velocity distribution functions of each ion component are also discussed by using maximum entropy principle. [ABSTRACT FROM AUTHOR]

In a recently developed nonlinear theory of Buneman instability, a simplifying assumption of self-similarity was imposed for the electron distribution function, based upon which, a set of moment kinetic equations was derived and solved together with nonlinear wave kinetic equation [P. H. Yoon and T. Umeda, Phys. Plasmas 17, 112317 (2010)]. It was found that the theoretical result compared reasonably against one-dimensional electrostatic Vlasov simulation. In spite of this success, however, the simulated distribution deviated appreciably from the assumed self-similar form during the late stages of nonlinear evolution. In order to rectify this shortcoming, in this paper, the distribution function is computed on the basis of rigorous velocity space diffusion equation. A novel theoretical scheme is developed so that both the quasilinear particle diffusion equation and the adiabatic dispersion relation can be solved for an arbitrary particle distribution function. Comparison with Vlasov simulation over relatively early quasilinear phase of the instability shows a reasonable agreement, despite the fact that quasilinear theory lacks coherent nonlinear effects as well as mode-mode coupling effects. [ABSTRACT FROM AUTHOR]

In the present paper, the weak turbulence theory for reactive instabilities, formulated in a companion paper [P. H. Yoon, Phys. Plasmas 17, 112316 (2010)], is applied to the strong electron-ion two-stream (or Buneman) instability. The self-consistent theory involves quasilinear velocity space diffusion equation for the particles and nonlinear wave kinetic equation that includes quasilinear (or induced emission) term as well as nonlinear wave-particle interaction term (or a term that represents an induced scattering off ions). We have also performed one-dimensional electrostatic Vlasov simulation in order to benchmark the theoretical analysis. Under the assumption of self-similar drifting Gaussian distribution function for the electrons it is shown that the current reduction and the accompanying electron heating as well as electric field turbulence generation can be discussed in a self-consistent manner. Upon comparison with the Vlasov simulation result it is found that quasilinear wave kinetic equation alone is insufficient to account for the final saturation amplitude. Upon including the nonlinear scattering term in the wave kinetic equation, however, we find that a qualitative agreement with the simulation is recovered. From this, we conclude that the combined quasilinear particle diffusion plus induced emission and scattering (off ions) processes adequately account for the nonlinear development of the Buneman instability. [ABSTRACT FROM AUTHOR]

In the present study, we analyze the data sets produced by a one-dimensional Vlasov–Poisson simulation of the weak electron beam-plasma instability to clarify the nonlinearity of the Langmuir turbulence excited by the weak-beam interaction. The growth of wave number modes is analyzed by using the momentum equation of the whole electrons. The analysis shows that the primary Langmuir wave mode is almost linear, while the nonlinear terms play important roles in the growth of the lower harmonic mode and the secondary higher harmonic mode. After the linear growth saturates, while the wave power of the primary mode is much larger than the other modes, linear and nonlinear interactions occurring in both lower harmonic and secondary higher harmonic modes are more active than those in the primary mode. Nonlinearity in the system comes from the advection rather than the ponderomotive forces. [ABSTRACT FROM AUTHOR]

In a recent paper it was suggested on the basis of weak turbulence theory that the collisionality of a plasma, coupled with nonlinear wave-particle interaction, is crucial for the acceleration of electrons by Langmuir turbulence to a superthermal energy level. In this Letter, fully nonlinear Vlasov and particle-in-cell (PIC) simulation techniques are employed to further verify this potentially important finding. The previous conclusion is fully confirmed by observing the expected difference between the Vlasov and PIC simulation results in the weak beam regime. However, in the strong beam regime, both the Vlasov and PIC simulations are found to produce a high-energy tail population, which indicates that there may be other mechanisms in the high beam speed situation, that are responsible for the generation the superthermal electrons. [ABSTRACT FROM AUTHOR]

Generation of harmonic Langmuir modes during beam-plasma interaction is studied by means of nonlinear theoretical calculations and computer simulations. The present Vlasov simulation of multiple harmonic Langmuir modes (up to 12th harmonics), generalizes the previously available simulations which were restricted to the second harmonic only. The frequency-wave-number spectrum obtained by taking the Fourier transformation of simulated electric field both in time and space shows an excellent agreement with the theoretical nonlinear dispersion relations for harmonic Langmuir waves. The saturated wave amplitude features a quasi-power-law spectrum which reveals that the harmonic generation process may be an integral part of the Langmuir turbulence. [ABSTRACT FROM AUTHOR]

The Langmuir wave turbulence generated by a beam-plasma interaction has been studied since the early days of plasma physics research. In particular, mechanisms which lead to the quasi-power-law spectrum for Langmuir waves have been investigated, since such a spectrum defines the turbulence characteristics. Meanwhile, the generation of harmonic Langmuir modes during the beam-plasma interaction has been known for quite some time, and yet has not been satisfactorily accounted for thus far. In paper I of this series, nonlinear dispersion relations for these harmonics have been derived. In this paper (paper II), generalized weak turbulence theory which includes multiharmonic Langmuir modes is formulated and the self-consistent particle and wave kinetic equations are solved. The result shows that harmonic Langmuir mode spectra can indeed exhibit a quasi-power-law feature, implying multiscale structure in both frequency and wave number space spanning several orders of magnitude. [ABSTRACT FROM AUTHOR]

Generation of electrostatic multiple harmonic Langmuir modes during beam-plasma interaction process has been observed in laboratory and spacebome active experiments, as well as in computer simulation experiments. Despite earlier efforts, such a phenomenon has not been completely characterized both theoretically and in terms of numerical simulations. This paper is a first in a series of three papers in which analytic expressions for harmonic Langmuir mode dispersion relations are derived and compared against the numerical simulation result. [ABSTRACT FROM AUTHOR]

The microscopic behavior of nitrogen atoms in the SiO2-SiC interface regions of n-channel lateral 4 H-SiC metal-oxide-semiconductor field effect transistors (MOSFETs) was studied using low-temperature electrically detected magnetic resonance spectroscopy and other techniques. The results show that nitrogen atoms eliminated shallow interface states observable at 20 K and further diffused into the channel region of the MOSFETs as shallow donors. These two behaviors enable nitrogen atoms to change the channel conductivity of SiC MOSFETs. [ABSTRACT FROM AUTHOR]

An electron paramagnetic resonance (EPR) study on fluorine-vacancy defects (FnVm) in fluorine-implanted silicon is demonstrated. Fluorine implantation is an important technology for Si microdevices and EPR measurements showed that this process created a variety of FnVm defects of different sizes (V2, V4, and V5). In FnVm, a Si–F bond exhibited a different chemical nature compared to a Si–H bond in hydrogen-vacancy complexes. The most primitive defect was FV2 (F0 center) and the final types were FnV5 (F1 center) and FnV2 (F2 center) which increased in annealing processes as low temperature as 200 °C. [ABSTRACT FROM AUTHOR]

The variable retention time phenomenon has recently been highlighted as an important issue in dynamic random access memory (DRAM) technology. Based on electrically detected magnetic resonance and simulation studies, we suggest that a single Si vacancy-oxygen complex defect is responsible for this phenomenon, when the defect is embedded in the near surface drain-gate boundary of a DRAM cell. [ABSTRACT FROM AUTHOR]

The extension and limitation of the existing one-dimensional kinetic-fluid model (Vlasov-MHD (magnetohydrodynamic) model), which has been used to analyze parametric instabilities of parallel propagating Alfvén waves, are discussed. The inconsistency among the given velocity distribution functions in the past studies is resolved through the systematic derivation of the multi-dimensional Vlasov-MHD model. The linear dispersion analysis of the present model indicates that the collisionless damping of the slow modes is adequately evaluated in low beta plasmas, although the deviation between the present model and the full-Vlasov theory increases with increasing plasma beta and increasing propagation angle. This is because the transit-time damping is not correctly evaluated in the present model. It is also shown that the ponderomotive density fluctuations associated with the envelope-modulated quasi-parallel propagating Alfvén waves derived from the present model is not consistent with those derived from the other models such as the Landau-fluid model, except for low beta plasmas. The result indicates the present model would be useful to understand the linear and nonlinear development of the Alfvénic turbulence in the inner heliosphere, whose condition is relatively low beta, while the existing model and the present model are insufficient to discuss the parametric instabilities of Alfvén waves in high beta plasmas and the obliquely propagating waves. [ABSTRACT FROM AUTHOR]