Boron Incorporation Research Articles

Investigation of boron incorporation in delta doped diamond layers by secondary ion mass spectrometry

Boron incorporation into ultra-thin boron doped epitaxial grown diamond layers of thickness of 1 to 2nm was investigated. Time of flight secondary ion mass spectroscopy was used to examine the boron concentration as a function of depth of the samples. The boron depth profiles were deconvoluted by modeling and measuring the depth resolution function with specially grown multiple delta doped layers on the same substrate. Boron incorporation in the delta layers as a function of substrate temperature and B/C ratio in the reactant gas was determined. A diamond deposition regime in which the doped delta layers with thickness of 1–2nm and with boron concentrations of about 4–5·1020 cm−3 was obtained. Such layers are suitable for implementation of two-dimensional hole “gas” in diamond with high mobility and high carrier concentrations.

BInGaN alloys nearly lattice-matched to GaN for high-power high-efficiency visible LEDs

InGaN-based visible light-emitting diodes (LEDs) find commercial applications for solid-state lighting and displays, but lattice mismatch limits the thickness of InGaN quantum wells that can be grown on GaN with high crystalline quality. Since narrower wells operate at a higher carrier density for a given current density, they increase the fraction of carriers lost to Auger recombination and lower the efficiency. The incorporation of boron, a smaller group-III element, into InGaN alloys is a promising method to eliminate the lattice mismatch and realize high-power, high-efficiency visible LEDs with thick active regions. In this work, we apply predictive calculations based on hybrid density functional theory to investigate the thermodynamic, structural, and electronic properties of BInGaN alloys. Our results show that BInGaN alloys with a B:In ratio of 2:3 are better lattice matched to GaN compared to InGaN and, for indium fractions less than 0.2, nearly lattice matched. Deviations from Vegard's law appear as bowing of the in-plane lattice constant with respect to composition. Our thermodynamics calculations demonstrate that the solubility of boron is higher in InGaN than in pure GaN. Varying the Ga mole fraction while keeping the B:In ratio constant enables the adjustment of the (direct) gap in the 1.75–3.39 eV range, which covers the entire visible spectrum. Holes are strongly localized in non-bonded N 2p states caused by local bond planarization near boron atoms. Our results indicate that BInGaN alloys are promising for fabricating nitride heterostructures with thick active regions for high-power, high-efficiency LEDs.

Band bowing and the direct-to-indirect crossover in random BAlN alloys

Boron-containing nitride alloys such as BAlN are being explored as novel members of the nitride family of materials for electronic and optoelectronic applications. Using hybrid density functional calculations we determine structural properties, band gaps, and band-gap bowing of random wurtzite BAlN alloys. The fundamental band gap of BN is indirect while AlN is a direct-band-gap semiconductor. This leads to a crossover in the band gap from direct to indirect at $28%$ boron. We find that the direct band gap experiences extreme bowing, leading to a fundamental gap that changes very little up to 17% boron incorporation.

Radiation response of cubic mesoporous silicate and borosilicate thin films

Abstract The radiation response has been studied of cubic mesoporous silicate and borosilicate thin films having different boron contents prepared using the block copolymer template Brij 58 and the dip coating technique. The degree of pore ordering of the films was analysed using low-angle X-ray diffraction and film thickness measured by X-ray reflectivity. For films calcined at 350 °C, the incorporation of boron resulted in a reproducible oscillatory variation in the d-spacing and intensity of the primary reflection as a function of boron content. A clear peak was observed in the d-spacing at 5–10 mol% boron incorporation. For borosilicate films of a given composition an overall suppression of d-spacing was observed as a function of aging time relative to films that did not contain boron. This was ascribed to a slow condensation process. The films were irradiated in pile with neutrons and with iodine ions at energies of 180 keV and 70 MeV. Neutron irradiation of the silicate thin films for periods up to 30 days and aged for 400 days resulted in little reduction in either d-spacing or intensity of the primary low-angle X-ray reflection indicating that the films retained their mesopore ordering. In contrast borosilicate films for which the B (n, α) reaction was expected to result in enhanced displacement damage showed much larger variations in X-ray parameters. For these films short irradiation times resulted in a reduction of the d-spacing and intensity of the primary reflections considerably beyond that observed through aging. It is concluded that prolonged neutron irradiation and internal α irradiation have only a small, although measurable, impact on mesoporous borosilicate thin films increasing the degree of condensation and increasing unit cell contraction. When these borosilicate films were irradiated with iodine ions, more profound changes occurred. The pore ordering of the films was significantly degraded when low energy ions were used. In some cases the degree of damage was such that no low-angle reflection could be observed. This degradation of pore ordering was confirmed in scanning electron microscopy images of the irradiated films.

Surface-Modified Ta3N5 Nanocrystals with Boron for Enhanced Visible-Light-Driven Photoelectrochemical Water Splitting.

Photocatalysts for water splitting are the core of renewable energy technologies, such as hydrogen fuel cells. The development of photoelectrode materials with high efficiency and low corrosivity has great challenges. In this study, we report new strategy to improve performance of tantalum nitride (Ta3N5) nanocrystals as promising photoanode materials for visible-light-driven photoelectrochemical (PEC) water splitting cells. The surface of Ta3N5 nanocrystals was modified with boron whose content was controlled, with up to 30% substitution of Ta. X-ray photoelectron spectroscopy revealed that boron was mainly incorporated into the surface oxide layers of the Ta3N5 nanocrystals. The surface modification with boron increases significantly the solar energy conversion efficiency of the water-splitting PEC cells by shifting the onset potential cathodically and increasing the photocurrents. It reduces the interfacial charge-transfer resistance and increases the electrical conductivity, which could cause the higher photocurrents at lower potential. The onset potential shift of the PEC cell with the boron incorporation can be attributed to the negative shift of the flat band potential. We suggest that the boron-modified surface acts as a protection layer for the Ta3N5 nanocrystals, by catalyzing effectively the water splitting reaction.

Highly tunable electronic properties in plasma-synthesized B-doped microcrystalline-to-amorphous silicon nanostructure for solar cell applications

Highly controllable electronic properties (carrier mobility and conductivity) were obtained in the sophisticatedly devised, structure-controlled, boron-doped microcrystalline silicon structure. Variation of plasma parameters enabled fabrication of films with the structure ranging from a highly crystalline (89.8%) to semi-amorphous (45.4%) phase. Application of the innovative process based on custom-designed, optimized, remote inductively coupled plasma implied all advantages of the plasma-driven technique and simultaneously avoided plasma-intrinsic disadvantages associated with ion bombardment and overheating. The high degree of SiH4, H2 and B2H6 precursor dissociation ensured very high boron incorporation into the structure, thus causing intense carrier scattering. Moreover, the microcrystalline-to-amorphous phase transition triggered by the heavy incorporation of the boron dopant with increasing B2H6 flow was revealed, thus demonstrating a very high level of the structural control intrinsic to the process. Control over the electronic properties through variation of impurity incorporation enabled tailoring the carrier concentrations over two orders of magnitude (1018–1020 cm−3). These results could contribute to boosting the properties of solar cells by paving the way to a cheap and efficient industry-oriented technique, guaranteeing a new application niche for this new generation of nanomaterials.

(Invited) Designing Symmetric and Asymmetric Morphology in Silicon Nanowires to Encode Advanced Electronic and Photonic Functionality

Silicon nanowires have been widely pursued as a technology for electronic, photonic, and renewable energy devices. Nevertheless, the implementation of nanowire technology has been limited by the extent to which the composition and morphology of wires can be controlled during synthesis. Here, we describe a bottom-up method—termed ENGRAVE (Encoded Nanowire GRowth and Appearance using VLS and Etching)—to modulate nanowire shape along the growth axis with sub-10 nanometer spatial resolution. Rapid modulation of phosphorus or boron incorporation during vapor-liquid-solid (VLS) growth encodes a high-resolution pattern of dopants in the wires. Subsequent solution processing is then used to selectively etch the wires, creating high resolution structures such as bow-ties, gratings, sawtooths, fractals, nanorods, sinusoids, and nanogaps. The capability to encode arbitrary morphology opens the door to new properties and functionality in the wires. For instance, we demonstrate how symmetric and periodic morphology can be used to design tunable photonic modes, enabling the coupling and waveguiding of light. In addition, we show how emergent electronic properties can be encoded through asymmetric morphology. The results highlight the broad set of new technologies that can be enabled through the design of precise sub-10 nanometer morphology in silicon nanowires.

Facial boron incorporation in hematite photoanode for enhanced photoelectrochemical water oxidation

Hematite (α-Fe2O3) is a promising photoanode material for light-driven water splitting to make solar fuels. Herein, boron incorporated hematite photoanodes are successfully fabricated by a simple impregnation treatment in borate solution before annealing the iron oxyhydroxide (FeOOH) precursor. X-ray diffraction, Raman and X-ray photoelectron spectroscopies revealed regional enrichment of boron and oxygen vacancy near the outmost surface of the photoanode, forming a unique heterostructure. The boron modified photoanodes exhibited significantly improved photoelectrochemical (PEC) water oxidation efficiency, with up to 37 times enhancement in photocurrent density, approaching 1.12mAcm−2 at 1.23VRHE under AM 1.5G illumination. Electrochemical impedance spectroscopy demonstrated a more favorable hole transfer process in the modified photoanode, which can be ascribed to the surface heterostructure induced build-in electric field, as well as the increase in carrier density introduced by oxygen vacancy.

Theoretical Raman spectrum and anharmonicity of tetrahedral OH defects in hydrous forsterite

Substitutional mechanisms involving hydrogen incorporation at vacant tetrahedral sites play a major role in water incorporation in olivine. Infrared (IR) absorption spectra of hydrous forsterite samples usually display a cluster of narrow and weakly anharmonic OH stretching bands at wavenumbers above 3500 cm −1 . A broader absorption band displaying pronounced temperature-dependent shift and broadening is commonly superimposed to this diagnostic spectrum and was tentatively assigned to interstitial OH groups. A less frequently observed band with similar temperature-dependent characteristics is related to a coupled incorporation of hydrogen and boron at the tetrahedral site. Here, we re-examine these interpretations by computing the theoretical Raman spectrum and investigating the local vibrational properties of OH groups at the tetrahedral site of forsterite. The present results show that the two anharmonic bands are both to be ascribed to the protonated O2 site in the clumped ( B , H ) Si x and the ( 4 H ) Si x defects. The peculiar orientation of the corresponding OH groups does not allow H-bond sharing and leads to efficient vibrational phase relaxation of the stretching mode through a hindered rotational mode coupled to the vibrational density of states of the host. The occurrence of interstitial OH groups previously proposed to interpret specific anharmonic bands of the forsterite IR spectrum is highly challenged by this new explanation. These results confirm that, at high pressure and high temperature, hydrogen incorporation in forsterite is essentially dominated by ( 4 H ) Si x defects.

Potential material for fabricating optical mirrors: polished diamond coated silicon carbide.

Polished diamond coated silicon carbide can be a potential candidate material for making optical mirrors, due to the excellent properties. At present, five typical types of diamond films are deposited on RB-SiC substrates by hot filament chemical vapor deposition, and then polished by mechanical polishing. It is found that the boron-doped micro-crystalline and undoped nano-crystalline composite diamond (BDMC-UNCCD) coated specimen performs the best before, during, and after polishing. The film surface composed of nano-sized diamond grains has relatively low surface roughness and hardness, which are beneficial for the efficient polishing, and under the present condition only such a surface can be completely polished to a homogeneous mirror surface. The micro-sized diamond grains and the boron incorporation in the underlying BDMCD layer can enhance the film-substrate adhesion, which plays an important role in the film integrity during the polishing or subsequent applications. In conclusion, the polished BDMC-UNCCD coated RB-SiC specimen indeed shows low surface roughness (Ra=5.41 nm), high hardness (71.47GPa), high elastic modulus (746GPa), favorable surface shape accuracy (RMS=0.083λ), and considerable reflectivity in the short-wavelength range.

Fluxing induced boron alloying in Fe-based bulk metallic glasses

In this work, we report on advanced insights into the effects of fluxing on Fe50Ni30P13C7 bulk metallic glasses. We find that the employed oxide fluxing agent results in significant incorporation of boron in the alloy by atom probe tomography analysis. It demonstrates that the improved glass-forming ability induced by fluxing attributes to not only the reduction of heterogeneous nucleation, but also boron alloying. In addition, the more densely packed microstructure of the fluxed alloys is also related to amount of boron addition. Such an understanding is of great importance to adequately process glass-forming liquids, in order to achieve optimized bulk metallic glass parts with enhanced thicknesses and improved mechanical properties.

Large-scale molecular dynamics modeling of boron-doped amorphous SiCO ceramics.

At high temperature, silicon oxycarbide (SiCO) exhibits excellent mechanical properties and thermal stability. The incorporation of boron in SiCO results in improved performance in creep temperatures. In this work, large-scale molecular dynamics calculations were applied to obtain amorphous SiCO structures containing boron. Phase separation of C-C, B-C and Si-O was achieved for three compositions, and silicon-centered mixed-bond tetrahedrons were reproduced successfully. As the boron content increases, the boron atoms tend to form B-C and B-Si bonds in the voids, which stretches the free carbon network in some instances, causing a increase in C-C distance. Young's modulus remains stable at high temperature for the high-carbon case, which indicates that the free carbon network plays a critical role in the structural and thermal stability of SiBCO. Graphical Abstract Three major typical structures in the cooling down process for silicon boron oxycarbide (Si5BC2O8). Bonds: red Si-O, blue Si-C, black C-C, green B-C, purple Si-B.

Proving the role of boron in the structure of fly-ash/borosilicate glass based geopolymers

A spectroscopic investigation was carried out in order to determine the boron evolution into the structure of fly-ash based geopolymers, integrated with borosilicate glass coming from pharmaceutical waste. Fourier transformed infra-red (FTIR) spectroscopy was used to define the type of bonds after geopolymerization. Various solid-state nuclear magnetic resonance (MAS-NMR) measurements were instrumental to evaluate the extent of network formation in the structure and to compare the type of environments among the geopolymerization products and the source materials. 11B NMR conducted firstly on a pure borosilicate glass sample and then on a geopolymeric sample evidenced a variation of the chemical shifts of the pattern, proving that boron oxide (B2O3) initially dissolved and then took part in polycondensation reactions. FTIR spectroscopy showed the characteristic peaks of a geopolymeric product, also proving that the effectiveness of the reaction was not affected by incorporation of boron.

Steam catalytic cracking of heavy naphtha (C12) to high octane naphtha over B-MFI zeolite

Continues consuming of fuel from fossil oil reservoirs due to the increase in energy demands encouraged scientists to use the pyrolysis of biomass in the production of clean energy. One of the most important product from the pyrolysis of biomass is dodecane. However, dodecane requires a further transformation in order to produce lighter hydrocarbons. Borosilicalite-1 (B-MFI) was synthesized with different mineralizer agents and utilized for steam catalytic cracking of dodecane. Furthermore, the amount of cooperative incorporation of boron to zeolitic framework contributes in adjusting the zeolitic acidity and consequently the amount of weak acid sites were observed to be proportional to the contents of boron. However, from pyridine-FTIR analysis, it was noticed that the acid site nature of borosilicalite-1 samples exhibited Brønsted acid site. Nevertheless, the presence of alkali fluoride as mineralizer agent enhanced the presence of boron in tetrahedral coordination system, which led to lower catalytic activity. While samples synthesized in the presence of alkali hydroxide were catalytically more active in steam catalytic cracking of dodecane due to its exhibit in trigonal coordination system. It was found that borosilicalite-1 was more stable when it was synthesized in the presence of sodium hydroxide as mineralizer agent rather than potassium hydroxide and the conversion was reached to 95% at 350°C with space velocity of 4h−1 when the Si/B ratio was 10.

Core-top calibration of B/Ca in Pacific Ocean Neogloboquadrina incompta and Globigerina bulloides as a surface water carbonate system proxy

Practical methods for reconstructing past ocean carbonate chemistry are needed to study past periods of ocean acidification and improve understanding of the marine carbonate system's role in the global climate cycles. Planktic foraminiferal B/Ca may fill this role, but requires better understanding and improved proxy calibrations. We used Pacific Ocean core-top sediments to generate new calibrations of the B/Ca proxy for past carbonate system parameters in two upwelling/subpolar species of asymbiotic planktic foraminifera (Globigerina bulloides and Neogloboquadrina incompta). Both species show significant positive correlation of B/Ca with calcite saturation (Ωcalcite) and carbonate ion concentration ([CO32−]) across a broad range of environmental conditions. This suggests a calcification rate control on B/Ca incorporation (as Ωcalcite regulates calcification rate), in agreement with recent inorganic calcite studies. This is also consistent with a surface entrapment model of trace element incorporation into CaCO3. In neither species is B/Ca significantly correlated with pH, suggesting that pH does not directly regulate boron incorporation, and that calculation of pH directly from foraminiferal B/Ca is not suitable. Correlations between B/Ca and [B(OH)4−], [B(OH)4−/HCO3−], and [B(OH)4−]/DIC) are weaker than with Ωcalcite. Boron partition coefficients (KD=[B/Ca]solid/[B(OH)4−/HCO3−]seawater) show little or no correlation with [CO32−] or temperature and vary widely, providing no support for application of KD to calculate carbonate system parameters from B/Ca. We also discuss potential effects of depth-related dissolution, temperature, and salinity on B/Ca. These empirical calibrations linking foraminiferal calcite B/Ca with Ωcalcite provide a strong tool for reconstructing the past ocean carbonate system and improve our understanding of the proxy's geochemical basis.

Geochemistry of metals and metalloids in siliceous sinter deposits: Implications for elemental partitioning into silica phases

Sinter deposits are formed by precipitation of silica from hydrothermal fluids that have reached the surface environment. They are commonly found around hot springs and represent surface expressions of underlying geothermal systems and/or low sulfidation epithermal gold-silver hydrothermal deposits. Several studies have reported ppm to weight percent concentrations of metals (e.g., Au, Ag, Cu) and metalloids (e.g., As, Sb, B) in sinters capping geothermal systems and epithermal gold-silver deposits. However, the relation between the maturity of the siliceous sinter and its metal enrichment remains unknown. Here we use geochemical and mineralogical data that link the silica crystallinity degree with trace metal and metalloid contents in sinter. In this paper, we provide in situ trace element data in metal-rich silica sinter samples from the Puchuldiza geothermal field in the Altiplano of northern Chile that record the complete diagenetic sequence from non-crystalline opal A to microcrystalline quartz. Combined SEM, XRD and LA-ICP-MS data show that the concentration of metals and metalloids in sinters from Puchuldiza display a strong correspondence with silica crystallinity. While arsenic and boron are predominantly enriched in the more amorphous silica phases (opal A/CT), gold and silver show higher concentrations in the more crystalline phases (opal C/quartz). Silica structural, morphological and geochemical transformations from its initial precipitation to its final maturation after diagenesis are responsible for this differential enrichment. During the initial stages, gold and silver are incorporated into silica microspheres as cationic species and/or metal nanoparticles or colloids, while arsenic and boron incorporation is controlled by As-bearing accessory minerals and Fe-oxyhydroxides. As diagenesis progresses and the crystallinity of silica increases, diffusion-driven processes such as Ostwald ripening may progressively enrich gold and silver in the sinter, while metalloids are depleted owing to the low retention of arsenic by silica. These findings indicate that the diagenetic transitions of silica, defined by significant structural changes that involve generation of surface defects and the creation of reactive sites, may play an important role in elemental uptake by silica in near surface environments.

Growth rate dependence of boron incorporation into BxGa1−xAs layers

This work provides a comprehensive study of the incorporation behavior of B in growing GaAs under molecular beam epitaxy conditions. Structural characterization of superlattices revealed a strong dependence of the BAs growth rate on the GaAs growth rate used. In general, higher GaAs growth rates lead to a higher apparent BAs growth rate, although lower B cell temperatures showed saturation behavior. Each B cell temperature requires a minimum GaAs growth rate for producing smooth films. The B incorporation into single thick layers was found to be reduced to 75–80% compared to superlattice structures. The p-type carrier densities in 1000nm thick layers were found to be indirectly proportional to the B content. Furthermore, 500nm thick BxGa1−xAs layers showed significantly lower carrier concentrations, indicating B segregation on the surface during growth of thicker layers.

Direct Imaging of Dopant Distribution in Polycrystalline ZnO Films

Two fundamental requirements of transparent conductive oxides are high conductivity and low optical absorptance, properties strongly dependent on the free-carrier concentration of the film. The free-carrier concentration is usually tuned by the addition of dopant atoms; which are commonly assumed to be uniformly distributed in the films or partially segregated at grain boundaries. Here, the combination of secondary ion mass spectroscopy at the nanometric scale (NanoSIMS) and Kelvin probe force microscopy (KPFM) allows direct imaging of boron-dopant distribution in polycrystalline zinc oxide (ZnO) films. This work demonstrates that the boron atoms have a bimodal spatial distribution within each grain of the ZnO films. NanoSIMS analysis shows that boron atoms are preferentially incorporated into one of the two sides of each ZnO grain. KPFM measurements confirm that boron atoms are electrically active, locally increasing the free-carrier concentration in the film. The proposed cause of this nonuniform dopant distribution is the different sticking coefficient of Zn adatoms on the two distinct surface terminations of the ZnO grains. The higher sticking coefficient of Zn on the c+ surface restricts the boron incorporation on this side of the grains, resulting in preferential boron incorporation on the c- side and causing the bimodal distribution.

Synthesis of thick and high-quality homoepitaxial diamond with high boron doping level: Oxygen effect

Heavily boron doped CVD diamond growth in oxygen-containing carbon/hydrogen gas mixtures was investigated. The dependence of boron incorporation efficiency on the oxygen content in the gas phase was studied, as well as the electrical characteristics of the grown layers. The changes in the microwave plasma discharge with the increase of boron (500 to 40,000ppm) at different oxygen contents (O/C=0.02, 0.1 and 0.5) was investigated by OES. The behavior of the BH emission line indicate an existence of a “reservoir” for boron due to the presence of oxygen, which limits the production of BH radicals up to B/C=10.000ppm. It is shown that thick (>100μm) heavily-doped diamond layers (boron concentration>1020cm−3) can be obtained in the oxygen-containing carbon/hydrogen gas mixtures at high power density growth conditions (MWPD=130W/cm3), allowing high quality deposition at a reasonably high growth rate 4μm/h.

High quality boron-doped epitaxial layers grown at 200°C from SiF4/H2/Ar gas mixtures for emitter formation in crystalline silicon solar cells

Controlling the doping profile in solar cells emitter and front/back surface field is mandatory to reach high efficiencies. In the current state of the art, these doped layers are made by dopant diffusion at around 900°C, which implies potential temperature induced damages in the c-Si absorber and for which a precise control of doping is difficult. An alternative solution based on boron-doped epitaxial silicon layers grown by plasma-enhanced chemical vapor deposition (PECVD) from 200°C using SiF4/H2/Ar/B2H6 chemistry is reported. The structural properties of the doped and undoped epitaxial layers were assessed by spectroscopic ellipsometry (SE), high resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD). The incorporation of boron has been studied via plasma profiling time of flight mass spectrometry (PP-TOFMS) and secondary ion mass spectrometry (SIMS) measurements. The boron-doped epitaxial layers revealed excellent structural and electrical properties even for high carrier concentrations (>1019cm-3). Sheet resistances between 100 and 130 Ω/sq can been obtained depending on the thickness and the doping concentration, which is within the range of targeted values for emitters in c-Si solar cells. Electrochemical capacitance voltage (ECV) revealed a uniform doping profile around 3.1019 cm-3 and by comparing with SIMS measurement a doping efficiency around 50% has been found.