Effect Of Si Doping Research Articles

Suppression of vacancy aggregation by silicon-doping in low-temperature-grown Ga1−xCrxN

Effect of Si doping on low-temperature grown GaCrN films has been investigated by positron annihilation spectroscopy. In undoped GaCrN films grown at 540 °C, vacancy clusters with sizes of V6–V12 were found to be responsible for positron trapping. Such vacancy clusters were considerably suppressed in Si-doped GaCrN films grown at 540 °C, although divacancies (VGaVN) still survived. The Si-doping may be one possible way to suppress vacancy aggregation during low temperature crystal growth, and the further methods to remove divacancies are required.

This forthcoming publication has been cancelled - Effects of Si-doping on magnetic properties of Ga1-xCrxN

This forthcoming publication has been cancelled - Effects of Si-doping on magnetic properties of Ga1-xCrxN

Investigation into the effect of Si doping on the performance of SrFeO3−δ SOFC electrode materials

In this paper we report the successful incorporation of silicon into SrFeO3−δ perovskite materials for potential applications as electrode materials for solid oxide fuel cells. It is observed that Si doping leads to a change from a tetragonal cell (with partial ordering of oxygen vacancies) to a cubic one (with the oxygen vacancies disordered). Annealing experiments in 5% H2/95% N2 (up to 800 °C) also showed the stabilization of the cubic form for the Si-doped samples under reducing conditions, suggesting that they may be suitable for both cathode and anode applications. In contrast to the cubic cell of the reduced Si doped system, reduction of undoped SrFeO3−δ leads to the formation of a brownmillerite structure with ordered oxide ion vacancies. SrFe0.90Si0.10O3−δ and SrFe0.85Si0.15O3−δ were analysed by neutron powder diffraction, and the data confirmed the cubic cell, with no long range oxygen vacancy ordering. Mossbauer spectroscopy data were also recorded for SrFe0.90Si0.10O3−δ, and indicated the presence of only Fe3+ and Fe5+ (i.e. disproportionation of Fe4+ to Fe3+ and Fe5+) for such doped samples. Conductivity measurements showed an improvement in the conductivity on Si doping. Composite electrodes with 50% Ce0.9Gd0.1O1.95 were therefore examined on dense Ce0.9Gd0.1O1.95 pellets in two different atmospheres: air and 5% H2/95% N2. In both atmospheres an improvement in the area specific resistance (ASR) values is observed for the Si-doped samples. Thus the results show that silicon can be incorporated into SrFeO3−δ-based materials and can have a beneficial effect on the performance, making them potentially suitable for use as cathode and anode materials in symmetrical SOFCs.

Investigation into the effect of Si doping on the performance of Sr1−yCayMnO3−δ SOFC cathode materials

In this paper we report the successful incorporation of silicon into Sr1-yCayMnO3-δ perovskite materials for potential applications in cathodes for solid oxide fuel cells. The Si substitution onto the B site of a (29)Si enriched Sr1-yCayMn1-xSixO3-δ perovskite system is confirmed by (29)Si MAS NMR measurements at low B0 field. The very large paramagnetic shift (~3000-3500 ppm) and anisotropy (span ~4000 ppm) suggests that the Si(4+) species experiences both Fermi contact and electron-nuclear dipolar contributions to the paramagnetic interaction with the Mn(3+/4+) centres. An improvement in the conductivity is observed for low level Si doping, which can be attributed to two factors. The first of these is attributed to the tetrahedral coordination preference of Si leading to the introduction of oxide ion vacancies, and hence a partial reduction of Mn(4+) to give mixed valence Mn. Secondly, for samples with high Sr levels, the undoped systems adopt a hexagonal perovskite structure containing face sharing of MnO6 octahedra, while Si doping is shown to help to stabilise the more highly conducting cubic perovskite containing corner linked octahedra. The level of Si, x, required to stabilise the cubic Sr1-yCayMn1-xSixO3-δ perovskite in these cases is shown to decrease with increasing Ca content; thus cubic symmetry is achieved at x = 0.05 for the Sr0.5Ca0.5Mn1-xSixO3-δ series; x = 0.075 for Sr0.7Ca0.3Mn1-xSixO3-δ; x = 0.10 for Sr0.8Ca0.2Mn1-xSixO3-δ; and x = 0.15 for SrMn1-xSixO3-δ. Composites with 50% Ce0.9Gd0.1O1.95 were examined on dense Ce0.9Gd0.1O1.95 pellets. For all series an improvement in the area specific resistances (ASR) values is observed for the Si-doped samples. Thus these preliminary results show that silicon can be incorporated into perovskite cathode materials and can have a beneficial effect on the performance.

The Effect of Si-Doping on the Release of Antibiotic from Hydroxyapatite Coatings

Herein, we show that incorporation of ions during biomimetic coating deposition may be utilized to tailor the drug loading capacity of hydroxyapatite (HA) coatings. Pure biomimetic HA (HA-B) and Si-doped equivalents (SiHA-B) where deposited by a biomimetic process onto titanium dioxide covered titanium substrates. The antibiotic Cephalothin was incorporated into the coatings by adsorptive loading and the release was studied in-vitro. SiHA-B coatings exhibited superior drug incorporation capacity compared to pure HA-B coatings, resulting in a drug release profile dominated by an initial 10 min burst effect while a more prolonged 10 hour release was observed from HA-B coatings. The results emphasize the possibility to impact the drug release kinetics from implant coatings by selective doping elements and the use of thin, biomimetic HA-coatings as drug delivery vehicles. Functionalizing metal implants with SiHA-B coatings presents an interesting strategy towards creating synergetic effects through ion- and antibiotic release and, hence, contributing both towards preventing post-surgical infections while at the same time enhancing the bone-bonding ability.

Effects of Si doping in high-quality AlN grown by MOVPE on trench-patterned template

The effects of Si doping on the structural properties of a high-quality AlN layer grown on a trench-patterned AlN/sapphire by metalorganic vapor phase epitaxy (MOVPE) were systematically studied. With a high Si doping concentration, void formation became much slower than that in undoped AlN film. This phenomenon was attributed to the anti-surfactant effect of Si in the growth process. Moreover, as the Si doping concentration increased, compressive stress was significantly relaxed in Si-doped AlN films. A high Si doping concentration of 1×1018cm−3 was successfully achieved for AlN grown at 1500°C.

Effect of Si doping on epitaxial lateral overgrowth of GaN: A spatially resolved micro-Raman scattering study

We report spatially resolved Raman scattering from Si-doped epitaxial laterally overgrown GaN structures to investigate spatial variations in stress and free electron concentration. The doping-induced increase in the free electron concentration is relatively higher in the laterally overgrown regions than in the coherently grown regions due to the increased contribution of the high-energy A1 longitudinal optical phonon–plasmon coupled mode. In addition, the E2(high) [E2(low)] phonon energy shifts downward (upward) more significantly in the laterally overgrown regions than in the coherently grown regions. The doping-induced Raman shifts of the E2(high) and E2(low) phonons in the laterally overgrown regions are approximately −0.6 and 0.11 cm−1, respectively, corresponding to the in-plane stress of ∼0.22 GPa.

Effect of Si doping in wells of AlGaN/GaN superlattice on the characteristics of epitaxial layer

An AlGaN/GaN superlattice grown on the top of a GaN buffer induces the broadening of the full width at half maximum of (102) and (002) X-ray diffraction rocking curves. With an increase in the Si-doped concentration in the GaN wells, the full width at half maximum of the (102) rocking curves decreases, while that of the (002) rocking curves increases. A significant increase of the full width at the half maximum of the (002) rocking curves when the doping concentration reaches 2.5 × 1019 cm−3 indicates the substantial increase of the inclined threading dislocation. High level doping in the AlGaN/GaN superlattice can greatly reduce the biaxial stress and optimize the surface roughness of the structures grown on the top of it.

Effect of Si Doping on the Crystal Structure of HVPE Grown Boron Phosphide

Boron Phosphide (BP) layers have been grown on Si (100) as a substrate for cubic GaN heteroepitaxy. Si heavy doping was attempted to reduce the threading dislocation density in the BP. To observe the effect on dislocations in BP by Si doping, we used cross-sectional transmission electron microscopy (XTEM). Also, Glow Discharge-Optical Emission Spectroscopy (GDOES) were used to evaluate the effect of Si doping. For the samples under the conditions (a) and (e), we found the formation of pits at BP surface and an increasing in the proportion of threading dislocations with an angle of 90 ° to the surface. We could not see a significant change in the threading dislocation density by Si doping under the conditions used in this paper.

Silicon nanowire anode: Improved battery life with capacity-limited cycling

Silicon nanowires grown on a stainless steel current collector were evaluated as Li ion battery anodes in an ionic liquid consisting of butyl-trimethyl ammonium bis(trifluoromethylsulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. The electrodes showed good performance in the ionic liquid electrolyte with a stable discharge capacity of ∼2000mAhg−1 and coulombic efficiency of 97% after 50 cycles. However, the large internal stresses caused by the volumetric expansion of the Si during lithiation limits the long-term cycle life of the battery in both ionic and organic electrolytes due in-part to the repeated disruption and reformation of the solid electrolyte interface layer on the Si. In contrast, when the same Si nanowire electrode was cycled at relatively shallow discharges, similar to those of carbon anodes, 320mAhg−1, the battery showed better performance with cycle life greater than 650 cycles and coulombic efficiency close to 100% in the ionic liquid electrolyte. Cycling at 1000mAhg−1 showed lifetimes in excess of 200 cycles in an organic electrolyte without cell degradation. The effect of Si doping, and amount of electrolyte in contact with the anode on the battery capacity and cycle life are also presented.

OPL volume 1424 Cover and Front matter

Recently, GaN has attracted much attention for short wavelength LEDs, LDs and future opto-electronic integrated devices. In our study, Boronmonophosphide(BP) grown on Si(100) by MOCVD is used for growing cubic-GaN (c-GaN). The epitaxial growth of GaN/BP/Si has been carried out. We observed the crystal defects by scanning electron microscope(SEM), transmission electron microscopy(TEM), and surface X-ray diffraction(XRD). The dislocation density in the BP layer markedly decreased with increasing the thickness. However the difference of the lattice constant between BP and Si leads to high dislocation densities in GaN layer. Therefore, the epitaxial growth of Si doped BP on Si has been carried out, in order to observe the effect of Si doping on BP crystalline quality. We observed the crystal defects by XRD and cross-sectional TEM. The dislocation of interfaces will be discussed.

Effects of Silicon Doping and Threading Dislocation Density on Stress Evolution in AlGaN Films

ABSTRACTIn-situ wafer curvature measurements were used to study the effect of Si doping on intrinsic growth stress during the metalorganic chemical vapor deposition (MOCVD) growth of AlxGa1-xN (x=0-0.62) layers on SiC substrates. Post-growth transmission electron microscopy (TEM) characterization was used to correlate measured changes in stress with changes in film microstructure. Si doping was found to result in the inclination of edge-type threading dislocations (TDs) in AlxGa1-xN which resulted in a relaxation of compressive stress and generation of tensile stress. The experimentally measured stress gradient was similar to that predicted by an effective climb model. Dislocation inclination resulted in a reduction in the TD density for Si-doped layers compared to undoped AlxGa1-xN likely due to increased opportunities for dislocation interaction and annihilation. The TD density, which increased with increasing Al-fraction, was found to significantly alter the stress gradients in the films. Film stress was also observed to play a role in TD inclination. In undoped AlxGa1-xN, TD inclination was observed only when the film grew under a compressive stress while in Si-doped AlxGa1-xN, TD inclination was observed independent of the sign or magnitude of the film stress. Si dopants are believed to alter the concentration of surface vacancies which gives rise to dislocation jog via a surface-mediated climb mechanism.

Comment on “The effects of Si doping on dislocation movement and tensile stress in GaN films” [J. Appl. Phys. 109, 073509 (2011)

In the publication by Moram et al. [J. Appl. Phys. 109, 073509 (2011)], some statements were made which disagree with the measurements presented by the authors of the article. In particular, silicon doping is claimed to suppress dislocation movement in GaN epitaxy hampering stress reduction during growth. We show that the data indeed prove the opposite, in agreement with prior publications.

Response to “Comment on ‘The effects of Si doping on dislocation movement and tensile stress in GaN films’” [J. Appl. Phys. 109, 073509 (2011)

Response to “Comment on ‘The effects of Si doping on dislocation movement and tensile stress in GaN films’” [J. Appl. Phys. 109, 073509 (2011)

Effect of Si doping on near-infrared emission and energy transfer of Bismuth in silicate glasses

We have studied the effects of Si doping on the near infrared (NIR) luminescence observed in low Bi doped ( 0.1mol% ) glasses and the energy transfer from Yb3+ to Bi. The broadband near infrared can only be observed when Si is introduced in the Bi-doped glass. The origin of this fluorescence can be attributed to Bi ions at low valence. Efficient energy transfer from Yb3+ to Bi NIR active ions is achieved by co-doping of Si. There is an increment of about ~29 times of the emission intensity from Bi-related active center as the Yb3+ concentration varies from 0 to 2.0mol% and the amount of Si is 0.05mol% under 980nm excitation. The possible mechanism of energy transfer from Yb3+ to Bi is also discussed.

Effect of Si-Doping on Thermal Stability and Diesel Oxidation Activity of Pt Supported Porous γ-Al2O3 Monolithic Catalyst

A series of different contents of Si-stabilized aluminas with high thermal stability were synthesized by the coprecipitation method and were used as the support of Pt diesel oxidation catalysts. The physicochemical properties of SiO2–Al2O3 (SA) and the catalytic performance of Pt/SiO2–Al2O3 (Pt/SA) were characterized in detail by TG–DTA, XRD, infrared spectroscopy, N2 adsorption, NMR, CO-TPD, and the catalytic activity evaluation of CO and C3H6 oxidations as well as NO reduction in simulating diesel exhaust. The results indicate that the presence of Si can remarkably enhance the thermal stability and phase transition temperature of alumina. It was also found that the catalytic activity is virtually independent of surface area, and only appropriate amount of Si doping can improve the diesel oxidation activity, as compared to pure Pt/Al2O3 under the same conditions as a result of the better dispersion of Pt on SA–W supports. The appropriate amount of Si doped can enhance the diesel oxidation activity of Pt/Al2O3 monolithic catalyst at the same condition as the result of the better dispersion of Pt on SiO2–Al2O3 samples.

Effect of Si-doping on InAs nanowire transport and morphology

The effect of Si-doping on the morphology, structure, and transport properties of nanowires was investigated. The nanowires were deposited by selective-area metal organic vapor phase epitaxy in an N2 ambient. It is observed that doping systematically affects the nanowire morphology but not the structure of the nanowires. However, the transport properties of the wires are greatly affected. Room-temperature four-terminal measurements show that with an increasing dopant supply the conductivity monotonously increases. For the highest doping level the conductivity is higher by a factor of 25 compared to only intrinsically doped reference nanowires. By means of back-gate field-effect transistor measurements it was confirmed that the doping results in an increased carrier concentration. Temperature dependent resistance measurements reveal, for lower doping concentrations, a thermally activated semiconductor-type increase of the conductivity. In contrast, the nanowires with the highest doping concentration show a metal-type decrease of the resistivity with decreasing temperature.

Investigation of the Si doping effect in β-Ga2O3 films by co-sputtering of gallium oxide and Si

A transparent electrode of Si doped β-Ga2O3 films for solar cells, flat panel displays and other devices, which consists of chemically abundant and ecological friendly elements of gallium and oxygen, was grown on silicon substrates by RF magnetron sputtering using sintered Ga2O3 and Si target. The Si composition in the β-Ga2O3 film is determined by electron dispersive X-ray spectroscopy. The X-ray photoelectron spectroscopy peak ratio of oxygen over gallium decreases with increasing Si content. It is concluded that Si substitutes for the Ga sites in the β-Ga2O3 film.

Si-doping effect on the enhanced hydrogen storage of single walled carbon nanotubes and graphene

We identified several parameters that correlate with the hydrogen physisorption energy and physicochemical properties of heteronuclear bonding in single-walled carbon nanotubes (SWCNT) and graphene. These parameters were used to find the most promising heteronuclear doping agents for SWCNTs and graphene for enhanced hydrogen storage capacity. Si-doping was showed to increase the amount of physisorbed hydrogen on such surfaces. Grand Canonical Ensemble Monte Carlo (GCMC) simulations showed that the hydrogen storage capacity of 10 at% Si-doped SWCNT (Si-CNT10) could reach a maximum of 2.5 wt%, almost twice the storage capacity of undoped SWCNTs, which were showed to reach a maximum capacity of 1.4 wt% at room temperature. To achieve this capacity, debundling effects of the uneven surfaces of Si-doped SWCNTs were found to be necessary. Similarly, 10 at% Si-doping on graphene (Si-GR10) was showed to increase the hydrogen storage capacity from 0.8 to 2.4 wt%.

Effect of Si doping on the photocatalytic activity and photoelectrochemical property of TiO2 nanoparticles

Abstract Si-doped TiO 2 nanoparticles with anatase crystalline phase were prepared by a hydrothermal method using acetic acid as the solvent. Photoelectrochemical studies showed that the photocurrent value for the 15% Si-doped TiO 2 electrode (54.4 μA) was much higher than that of the pure TiO 2 electrode (16.7 μA). In addition, the 15% Si-doped TiO 2 nanoparticles displayed the highest photocatalytic activity under ultraviolet light irradiation. So doping suitable amount of Si in TiO 2 nanoparticles was profitable for transferring photogenerated electrons and inhibiting the recombination of photogenerated electrons and holes. As a result, the photocatalytic activity of TiO 2 nanoparticles was improved.