Effect Of Carbon Impurities Research Articles

Effect of carbon impurity on the dislocation climb in epitaxial GaN on Si substrates

We investigate the effect of C doping on dislocation behaviors in GaN grown on Si substrates. A moderate C doping can promote dislocation climb and reduce the dislocation density. With further increasing the C concentration, the dislocation density will increase. In addition, C doping has more influence on edge dislocation than screw dislocation. The stress evolution in the GaN layer is also investigated and the result is consistent with the dislocation behaviors. We thus suggest a mechanism in that C impurities are incorporated into different lattice locations in GaN with increasing the doping level, which can explain the dislocation behaviors.

Effects of carbon impurity in ALD-Al2O3 film on HAXPES spectrum and electrical properties of Al2O3/AlGaN/GaN MIS structure

In this study, the effects of carbon impurity in the atomic layer deposited-Al2O3 film on the hard X-ray photoelectron spectroscopy (HAXPES) spectra and the electrical properties of metal–insulator–semiconductor (MIS) structure were measured. The carbon concentration in the Al2O3 film was adjusted by varying the deposition conditions (precursor: trimethylaluminum, Al(CH3)3, or dimethylaluminum hydride, Al(CH3)2H, oxidant, and deposition temperature) in the atomic layer deposition process. The HAXPES measurements revealed the correlation between full width at half maximum (FWHM) of Al 1 s and O 1 s spectra and the carbon concentration in the Al2O3 film. Furthermore, the negative charges in the Al2O3 film could change the FWHM, attributed to the carbon impurity. The correlation between the carbon concentration and the electrical characteristics of the Al2O3/AlGaN/GaN MIS structure was analyzed. The interface state density and the effective charge density were dependent on the carbon concentration in the Al2O3 film.

Effects of carbon impurities on the performance of silicon as an anode material for lithium ion batteries: An ab initio study

Silicon is widely used in the semiconductor industry and has recently become very attractive as a lithium ion battery anode due to its high capacity. However, volume changes associated with repeated lithiation–delithiation cycles expose fresh silicon surfaces to the electrolyte, causing irreversible side reactions. Moreover, silicon suffers from a poor electronic conductivity at a low lithium content. Carbon impurities originating at synthesis or resulting from subsequent contact with other electrode components are often neglected. However, atomistic simulations reveal that dissolved carbon decreases the local potential energy surface by drawing the electron density from silicon to form polar covalent C–Si bonds that are stronger than the non-polar covalent Si–Si bonds they replace. This leads to a higher density and elastic stiffness, regardless of the interstitial lithium concentration. Substitutional carbon also reduces the mobility of silicon self-vacancies and interstitial lithium by increasing their diffusion barriers by 24.7 and 27.3 kJ mol−1, respectively. Moreover, the [carbon, silicon vacancy] complex is basically stable, while the [carbon, lithium] complex is found to become stable against both single defects at a spacing of 4.72 Å. The minimum energy paths ultimately demonstrate that both the interstitialcy and dissociative mechanisms are mainly responsible for carbon diffusion in silicon.

6.2: Invited Paper: Effect of carbon impurity on the performance of GaN‐based laser diodes

6.2: <i>Invited Paper:</i> Effect of carbon impurity on the performance of GaN‐based laser diodes

Effects of carbon impurity on tritium diffusion and helium formation in γ-LiAlO2 pellets: A first-principles study

Gamma-phase lithium aluminate (γ-LiAlO2) in the form of annular pellets is used as a breeding material in tritium-producing burnable absorber rods (TPBARs) for the production of tritium by thermal neutron irradiation of 6Li. Significant radiation damage occurs in γ-LiAlO2 due to neutrons, and tritium and helium (He) nuclei, which recoil through the crystal. The radiation-damaged crystal is rich with vacancies and impurities such as carbon (C) that can act as tritium trapping sites. The presence of C impurities can hinder 3H diffusivities significantly. Here, we studied the effect of C impurities on 3H diffusivity and energy barriers in γ-LiAlO2 using first-principles density functional theory. In addition, we studied the He diffusion in an undefective γ-LiAlO2. We calculated the energy barrier for diffusion in γ-LiAlO2 to be 0.98 eV for substitutional 3H in the presence of a C impurity. At 600 K, the corresponding diffusion coefficient was calculated to be 7.98×10-14m2/s. Similarly, we calculated the energy barrier for He diffusion to be 0.12 eV, which was along the crystallographic c-direction. The corresponding diffusion coefficient for He at 600 K was calculated to be 6.8×10-7m2/s. This work may open further theoretical and experimental avenues on impurity effects and release of He from γ-LiAlO2.

Effects of Carbon Impurity in Monocrystalline Silicon on Electrical Properties and the Mechanism Analysis of PIN Rectifier Diodes

Carbon impurities are common defects in monocrystalline silicon and have negative effects on the electrical performance of electronic devices. In the present work, the effects of carbon impurities in monocrystalline silicon on the electrical properties of PIN rectifier diodes with different carbon concentrations were investigated by electrical performance tests, anisotropic preferential etching, Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS). It was found that with the increasing carbon concentration, the reverse leakage current (IR) increased rapidly, the time of reverse recovery (TRR) and the ratio of the average reverse withstand voltage to the theoretical value decreased rapidly, and the forward voltage drop ( $V_{f}$ ) increased significantly. Further, with the rising carbon concentration, bulk oxidation-induced defects (B-OSF) changed from dislocation-dominated to stacking fault-dominated and the stacking fault length increased gradually. [ $C_{i}-{O}_{i}$ ] carbon centers of interstitial carbon and interstitial oxygen with a wide absorption band were detected by FTIR. The existence of stacking dislocation defects and carbon-oxygen complexes [ $C_{i}-{O}_{i}$ ] was confirmed by TEM and EDS. It was pointed out that substitutional carbon ( $C_{s}$ ) captured interstitial silicon atoms, changed into interstitial carbon ( $C_{i})_{\mathrm {}}$ in the silicon substrate, and formed [ $C_{i}-{O}_{i}$ ] complexes of interstitial carbon and interstitial oxygen after high-temperature diffusion, and these complexes acted as heterogeneous nucleation centers to promote the formation and growth of oxygen precipitation. Due to the volume strain energy, interstitial silicon atoms and dislocations were continuously released to promote oxygen atoms during the growth process of carbon-oxygen complexes. The formation and growth of B-OSF defects caused the “impurity piercing pipe” effect. These defects acted as defect recombination centers and deteriorated the electrical performance of the PIN rectifier diodes.

Compensation Effect of Carbon Impurities on the Resistivity of p-GaN

Compensation Effect of Carbon Impurities on the Resistivity of p-GaN

Effects of carbon impurity on the ignition of deuterium-tritium targets under the relativistic shock waves

One of the main concerns about the ignition and burn of deuterium-tritium (DT) plasma is the negative effect of impurities that can get into the thermonuclear fuel during target compression on the ignition of an inertial confinement fusion (ICF) target. So, the ignition condition of the spherical DT plasma of the ICF target in the presence of high-density carbon impurities at an arbitrary concentration is found. The ignition criterion of nuclear fusion plasmas is investigated using a two-temperature model derived from a common model. The ignition criterion is described by a surface in the three-dimensional space. This surface is defined by the electron and ion temperatures, Te and Ti, and the plasma density times the hot spot dimension, ρ·R, for different concentrations of impurities. In this paper, a two-temperature laser induced shock wave is used. We found that one needs a laser intensity of 7.5 × 1021 W/cm2, a pulse duration of 1ps, and an energy of 0.44 kJ that induces a compression of κ = 4 to ignite a pure DT pre-compressed target at about 500 g/cm3. Given the constant intensity of the laser, the increase in the carbon impurity concentration increases the alpha energy deposition in the igniter zone; on the other hand, the temperature of the igniter zone decreases as a result of high losses of power densities, so that for impurity values of more than 20%, practically no hot spots are formed.

Influence of carbon impurities and oxygen vacancies in Al2O3 film on Al2O3/GaN MOS capacitor characteristics

Effects of carbon impurities and oxygen vacancies in Al2O3 film on the characteristics of Al2O3/GaN MOS capacitors were studied using the different atomic layer deposition (ALD) precursor and high-pressure water vapor annealing (HPWVA). Trimethyl aluminum (TMA: Al(CH3)3) and dimethyl aluminum hydride (DMAH: Al(CH3)2H) were used as ALD precursors to control the carbon impurities. On the other hand, oxygen vacancies in Al2O3 film were suppressed using the HPWVA. The DMAH precursor reduced the concentration of carbon impurities in the ALD Al2O3 film. It was found that the interface trap density (Dit) was mainly affected by the carbon impurities rather than the oxygen vacancies at the Al2O3/GaN interface. On the other hand, voltage stress induced flat band voltage (VFB) shift was attributed to both the carbon impurities and the oxygen vacancies.

Effects of carbon impurities on the power radiation and tungsten target erosion in EAST

Tungsten (W) and Carbon (C) are, respectively, used as the plasma-facing materials for upper and lower divertors in EAST. This provides an opportunity to study the plasma performance with both W and C divertors simultaneously. In this work, simulations are carried out by using the edge fluid-plasma/kinetic-neutral code SOLPS5.0-EIRENE99, with emphasis on the C impurity transport and its effect on the power radiation and erosion of the upper W divertor target. Three typical magnetic field equilibrium configurations, i.e., lower single null, upper single null (USN), and double null (DN), are studied. The main deuterium (D) plasma and C impurities at each ionization state and their neutrals are considered in the simulation. The SOLPS output such as averaged incident ion energy and particle flux density of each species are used to calculate the erosion rate of W walls using the empirical formula for physical sputtering yield. The transport and performance of C impurities on different plasma conditions of each configuration are investigated by changing the C source strength and upstream plasma density. The upper W target erosion by C ions under different conditions is also evaluated. The simulation results indicate that (1) carbon is a strong radiator in EAST divertor temperatures of 10–20 eV; (2) the amount of carbon transported from the lower carbon divertor to the upper tungsten divertor in both USN and DN configurations is predicted to be too small to cause significant W sputtering; and (3) C6+ dominates upper W erosion in the DN case.

Effect of carbon impurity in irradiated mixed uranium–plutonium nitride on the phase composition upon β−-decay of fission products

As shown by thermodynamic modeling, accumulation of fission products in the course of irradiation of mixed uranium–plutonium nitride containing 0.25 wt % C impurity leads to the formation of a multicomponent carbonitride solid solution containing U, Pu, Am, Np, Zr, Y, lanthanides, and also separate carbide (UMoC2, U2RuC2, URu3C0,7, BaC2, SrC2) and nitride (U2N3) phases and intermetallic compounds U(Ru, Rh, Pd)3. The β−-decay of metallic radionuclides in separate carbide phases of spent nuclear fuel leads to changes in their chemical compositions. The transformation kinetics of separate dicarbide (89SrC2 → 89YC2, 90SrC2 → 90YC2 → 90ZrC + C, 140BaC2 → 140LaC2 → 140CeC2) and complex carbide (U99MoC2 → UC2 + 99Tc) phases was calculated.

Eliminated Phototoxicity of TiO2 Particles by an Atomic-Layer-Deposited Al2 O3 Coating Layer for UV-Protection Applications.

We demonstrate the conformal coating of an ultrathin Al2 O3 layer on TiO2 nanoparticles through atomic layer deposition by using a specifically designed rotary reactor to eliminate the phototoxicity of the particles for cosmetic use. The ALD reactor is modified to improve the coating efficiency as well as the agitation of the particles for conformal coating. Elemental and microstructural analyses show that ultrathin Al2 O3 layers are conformally deposited on the TiO2 nanoparticles with a controlled thickness. Rhodamine B dye molecules on Al2 O3 -coated TiO2 exhibited a long life time under UV irradiation, that is, more than 2 h, compared to that on bare TiO2 , that is, 8 min, indicating mitigation of photocatalytic activity by the coated layer. The effect of carbon impurities in the film resulting from various deposition temperatures and thicknesses of the Al2 O3 layer on the photocatalytic activity are also thoroughly investigated with controlled experimental condition by using dye molecules on the surface. Our results reveal that an increased carbon impurity resulting from a low processing temperature provides a charge conduction path and generates reactive oxygen species causing the degradation of dye molecule. A thin coated layer, that is, less than 3 nm, also induced the tunneling of electrons and holes to the surface, hence oxidizing dye molecules. Furthermore, the introduction of an Al2 O3 layer on TiO2 improves the light trapping thus, enhances the UV absorption.

The effect of carbon impurities on molybdenum surface morphology evolution under high-flux low-energy helium ion irradiation

We report on the role of carbon (C) impurities, in molybdenum (Mo) fuzz evolutions on Mo surface during 100 eV He+ ion irradiations. In this study we considered 0.01, 0.05, and 0.5% C+ ion impurities in He+ ion irradiations. For introducing such tiny C+ ion impurities, gas mixtures of He and CH4 have been chosen in following ratios; 99.95: 0.05, 99.75: 0.25, and 97.5: 2.5. Apart from these three cases, two additional cases, 100% He+ ion (for Mo fuzz growth due to only He+ ions) and 100% H+ ion (for confirming the significance of tiny 0.04–2.0% H+ ions in terms of Mo fuzz evolutions on Mo surface, if any), have also been considered. Ion energy (100 eV), ion fluence (2.6 × 1024 ions m−2), and target temperature (923 K) were kept constant for each experiment and their selections were based on our previous studies [1,2]. Our study shows homogeneously populated and highly dense Mo fuzz evolutions on entire Mo surface for 100% He+ ion irradiation case. Enhancement of C+ ion impurities in He+ ions causes a sequential reduction in Mo fuzz evolutions, leading to almost complete prevention of Mo fuzz evolutions for 0.5% C+ ion impurity concentrations. Additionally, no fuzz formation for 100% H+ ion irradiation at all, were seen (apart from some tiny nano-structuring, in very limited regions). This indicates that there is no significant role of H+ ions in Mo fuzz evolutions (at least for such tiny amount, 0.04–2.0% H+ ions). The study is significant to understand the behavior of potential high-Z plasma facing components (PFCs), in the, presence of tiny amount of C impurities, for nuclear fusion relevant applications.

Influence of carbon dopants on the structure, elasticity and lattice dynamics of Ti5Si3Cx Nowotny phases

Density functional theory studies on the Ti5Si3Cx systems with various concentrations of carbon impurities () are reported. The effects of interstitial carbon atoms on crystal and electronic structures, and on the elastic and vibrational properties of the Ti5Si3Cx compound are analysed and discussed. The results of the present investigations indicate not only strong bonding between carbon atoms and their neighbouring titanium atoms, but also the effects of carbon impurities on the atomic bonds beyond the immediate proximity of the dopants. These determine to a great extent the electron densities of states, and the structural and elastic properties of the Ti5Si3Cx Nowotny phases. Although carbon atoms tend to stabilise Ti5Si3Cx phases, they also have a negative effect on their ductile properties. The strong impact of carbon impurities on the lattice dynamics of Ti5Si3Cx compounds is revealed by the phonon and Raman spectra, which remain sensitive to changes in the interatomic distances. In C-doped systems the phonon bands originating from the vibrations of carbon impurities appear at high frequencies and remain well-separated from the lower lying phonon bands dominated by the vibrations of Ti and Si sublattices. The lower frequency phonon bands also experience changes due to the incorporated dopants. Impurities occupying the interstitials of the Ti5Si3 lattice are responsible for the appearance of new infrared active and optically inactive modes of A2u, E1u and E2u symmetries, leaving the number of Raman active modes unchanged. Modifications to the dynamical properties of ternary Ti5Si3Cx phases manifest themselves via shifts and the suppression of phonon peaks as well as the emergence of new phonon peaks which are absent in the binary Ti5Si3 system. The observed effects become enhanced with an increased concentration of carbon impurities.

Role of carbon impurities on the surface morphology evolution of tungsten under high dose helium ion irradiation

The effect of carbon impurities on the surface evolution (e.g., fuzz formation) of tungsten (W) surface during 300 eV He ions irradiation was studied. Several tungsten samples were irradiated by He ion beam with a various carbon ions percentage. The presence of minute carbon contamination within the He ion beam was found to be effective in preventing the fuzz formation. At higher carbon concentration, the W surface was found to be fully covered with a thick graphitic layer on the top of tungsten carbide (WC) layer that cover the sample surface. Lowering the ion beam carbon percentage was effective in a significant reduction in the thickness of the surface graphite layer. Under these conditions the W surface was also found to be immune for the fuzz formation. The effect of W fuzz prevention by the WC formation on the sample surface was more noticeable when the He ion beam had much lower carbon (C) ions content (0.01% C). In this case, the fuzz formation was prevented on the vast majority of the W sample surface, while W fuzz was found in limited and isolated areas. The W surface also shows good resistance to morphology evolution when bombarded by high flux of pure H ions at 900 °C.

Study on effects of carbon impurities and oxygen vacancies in amorphous alumina phosphor prepared via a solution method

The amorphous alumina phosphors without containing expensive or toxic elements were prepared via a solution method. The obtained sample indicates bluish-white emission centered at 390–430nm by UV excitation. According to the measurement results of Electron Spin Resonance (ESR), Fourier Transform Infrared Spectroscopy (FT-IR) and organic microanalysis, it is found that the carbon impurities exist in the sample and they are essential for luminescence. On the other hand, 27Al NMR measurements indicate the presence of Al of 5-coordination. Moreover, there is good correspondence among the excitation spectra of the emission samples, the experimental optical properties of amorphous alumina, and the calculated oxygen vacancies levels in amorphous alumina model. Therefore, the new luminescence mechanism can be proposed as follows; the electrons in valence band are excited to oxygen vacancies bands by UV light and return to ground state through the carbon impurities band, being accompanied by the bluish-white emission.

High pressure synthesis of BN and BCN crystals and their functionalization

Hexagonal BN (hBN) and cubic BN (cBN) are known as the representative crystal structures of BN. The former is chemically and thermally stable, and has been widely used as an electrical insulator and heat-resistant materials. The latter, which is a high-density phase, is an ultra-hard material second only to diamond. Recently, some progresses in the synthesis of high purity BN crystals were achieved by using Ba-BN as a solvent material at high pressure crystal growth [1]. Band-edge natures (cBN Eg=6.2eV and hBN Eg=6eV) were characterized by their optical properties. The key issue to obtain high purity crystals is to reduce oxygen and carbon contamination in the growth circumstances. It should be emphasized that hBN exhibits attractive potential for deep ultraviolet (DUV) light emitter [2 ] and also superior properties as substrate of graphene devices [3]. In this study, the effect of carbon impurity in BN is investigated. Three types of experimental approaches were carried out; (1) synthesis of high purity hBN single crystals and its characterization with respect to residual carbon, (2) high temperature solid state diffusion of carbon into hBN and its characterization, and (3) high temperature annealing of turbostratic B-C-N(t-BCN) compound under high pressure. t-BCN flakes obtained by chemical vapour deposition process was annealed near 3000C and 2GPa so as to become well crystallized.At annealing near 3000C at 2GPa with graphite, carbon incorporation of 1E21/cm3 in hBN was achieved with exhibiting totally different Cathode Luminescence spectra feature with high purity hBN crystals. Since major carbon contribution may affect the crystal structure of the 2-D layers stacking in hBN system, phase stability of BCN ternary phase will be introduced by the experimental results of high temperature annealing. Furthermore, effect of carbon impurity upon the synthesis of wurtzite BN from highly crystalline hBN via martensitic phase transformation will also be introduced.

Impact of carbon impurities on the confinement of high-ion-temperature discharges in the Large Helical Device

Effects of carbon impurities on the thermal confinement properties were discussed for carbon-pellet-injected high-Ti discharges in the Large Helical Device (LHD). To clarify their role, the amounts of carbon impurities introduced into plasmas were scanned by varying the number of injections in a discharge or the size of the pellet, and the changes of thermal confinement properties with these variations were examined. In all cases, strong correlations between the densities of carbon impurities and the thermal diffusivities of plasmas were found. Thermal diffusivities were small when the carbon densities were greater than a certain value, e.g. ∼1.5 × 1017 m3 at r/a ≈ 0.72, and the thermal diffusivity degraded drastically below this density. This indicates the existence of a threshold density of carbon impurity for an improved confinement in plasmas. Combined with the formation of the impurity hole, the variation of confinement property with carbon density can explain the degradation of ion temperature in high-Ti discharges with carbon pellet injection in the LHD.

Ab initio study of dielectric function of C-substituted single walled boron nanotubes

We report dielectric function related optical properties namely dielectric constant, static dielectric constant, and absorption coefficients of C-substituted hexagonal boron nanotubes. The optical properties were computed for parallel and perpendicular polarized light in the framework of density functional theory. In this regard, three models of BNTs namely armchair (3,3), zigzag (5,0), and chiral (4,2) have been undertaken for probing the effect of carbon impurity. Our calculations show high dielectric constant of armchair and chiral BNTs for parallel polarized light and magnitude becomes smaller for higher impurity concentration, while zigzag BNT exhibits reverse trend for high impurity concentration. For perpendicular polarized light, the magnitude of dielectric constant e 1(ω) is decreased and shifts at higher frequencies. The absorption is revealed highest for armchair followed by zigzag and chiral BNTs independent of impurity concentration. The intensity of absorption gets weaken for higher concentration. The chiral BNTs show smaller but uniform absorption in smaller frequency range results in uniform field emission. These findings are also compared with available experimental and theoretical results. These metallic nanotubes are promising candidate as interconnects for nanodevices as well as field emission devices.

Electronic properties of C-substituted boron nanotubes: a first principles study

The pseudopotential calculations have been performed to study the effect of carbon impurity on the electronic nature of hexagonal ultrathin boron nanotubes. The structural stability and electronic properties of C-substituted BNTs have been evaluated by first principles calculations. Three conformations of BNTs viz. armchair (3,3), zigzag (5,0), and chiral (4,2), have been considered for examining the effects of carbon substitution. It is observed that carbon substituted hexagonal ultrathin BNTs become energetically more stable in contrast to pristine ones. It is revealed that all the C-substituted hexagonal BNTs are metallic and independent of chirality & impurity concentration. Thus, the chirality of C-substituted BNTs is controlled to a certain extent. These findings are also compared with available experimental and theoretical results. These metallic nanotubes are promising candidate as interconnects for nanodevices as well as field emission devices.