Silicon Doping Level Research Articles

Optimizing silicon doping levels for enhanced osteogenic and angiogenic properties of 3D-printed biphasic calcium phosphate scaffolds: An in vitro screening and in vivo validation study

Biphasic calcium phosphate (BCP) ceramics are valued for their osteoconductive properties but have limited osteogenic and angiogenic activities, which restricts their clinical utility in bone defect repair. Silicon doping has emerged as an effective strategy to enhance these biological functions of BCP. However, the biological impact of BCP is influenced by the level of silicon doping, necessitating determination of the optimal concentration to maximize efficacy in bone repair. This study investigated the effects of silicon doping on both the physicochemical and biological properties of BCP, with a specific focus on osteogenic and angiogenic potentials. Results indicated that silicon doping exceeding 4 mol.% led to the formation of α-TCP, accelerating BCP degradation, enhancing silicon ion release, and promoting mineralization product formation. Simultaneously, silicon doping increased the porosity of BCP scaffolds, which typically reduces their compressive strength. Nevertheless, scaffolds doped with ≤4 mol.% silicon maintained compressive strengths exceeding 2 MPa. In vitro biological experiments indicated that higher levels of silicon doping (≥6 mol.%) partially inhibited the successful differentiation of stem cells and the vascularization of endothelial cells. Optimal conditions for promoting osteogenic differentiation and angiogenesis were identified between 2 and 4 mol.% silicon doping, with an optimal level of approximately 4 mol.%. Subsequent in vivo experiments confirmed that BCP scaffolds doped with 4 mol.% silicon effectively promoted vascularization and new bone formation, highlighting their potential for clinical bone defect repair.

Uniform Tendency of Surface Dipoles Across Silicon Doping Levels and Types of H‐Terminated Surfaces

AbstractThe termination of surface‐dangling bonds on silicon through hydrogen atoms, also known as Si–H, can achieve chemical passivation and reduce surface states in the electronic bandgap, thus altering electronic properties. Through a comprehensive study of doping levels (1014–1020 cm−3) and types (n and p), a consistent surface dipole trend induced by Si–H termination is discovered. It is achieved by redistributing surface charges and establishing thermal equilibrium with the chemical bond. To resolve this, the surface work function, surface electron affinity, and the energy difference between the valence band and the Fermi level are measured by employing the Kelvin probe, X‐ray photoelectron spectroscopy, and photoelectron yield spectroscopy methods. These findings are further validated through ab initio simulations. This finding has immense implications not only for eliminating electronic defects at semiconductor interfaces, which is crucial in microelectronics but also for developing and engineering hybrid interfaces and heterojunctions with controlled electronic properties.

High current field emission from Si nanowires on pillar structures

We investigate the influence of the geometry and doping level on the performance of n-type silicon nanowire field emitters on silicon pillar structures. Therefore, multiple cathodes with 50 by 50 pillar arrays (diameter: 5 μm, height: 30 μm, spacing: 50 μm) were fabricated and measured in diode configuration. In the first experiment, we compared two geometry types using the same material. Geometry 1 is black silicon, which is a highly dense surface covering a forest of tightly spaced silicon needles resulting from self-masking during a plasma etching process of single crystal silicon. Geometry 2 are silicon nanowires, which are individual spaced-out nanowires in a crownlike shape resulting from a plasma etching process of single crystal silicon. In the second experiment, we compared two different silicon doping levels [n-type (P), 1–10 and <0.005 Ω cm] for the same geometry. The best performance was achieved with lower doped silicon nanowire samples, emitting 2 mA at an extraction voltage of 1 kV. The geometry/material combination with the best performance was used to assemble an integrated electron source. These electron sources were measured in a triode configuration and reached onset voltages of about 125 V and emission currents of 2.5 mA at extraction voltages of 400 V, while achieving electron transmission rates as high as 85.0%.

Synthesis and photocatalytic properties of silicon-doped TiO2 nanotubes

In this study, we present the synthesis and photocatalytic properties of Silicon (Si)-doped TiO2 nanotubes (TNTs) using the hydrothermal method. The doping level of Silicon, expressed as the dopant (Si/(Si + Ti)) molar ratio, was varied within the range of 1–30 %. X-ray diffraction analysis confirmed the presence of the nanocrystalline anatase phase in both pristine and Silicon-doped TNTs. Significantly, we observed an interesting enhancement in the crystallinity and purity of the anatase phase upon incorporating Silicon into TNTs, a finding that has not been previously reported. The light absorption spectra of the doped TNTs exhibited a Red Shift, with absorption edges shifting from 375 nm to 410 nm compared to undoped TNTs. The photodegradation experiments demonstrated the favorable photocatalytic activity of the Silicon-doped TNTs with a fast response to stimulus light. The red-shifted absorption spectra, coupled with the enhanced crystallinity of the anatase phase, contributed to improved performance in the degradation of target compounds.

Label-free DNA detection using silver nanoprism decorated silicon nanoparticles: Effect of silicon nanoparticle size and doping levels

In the present work, we have fabricated silver nanoprism (AgNPrs)/silicon nanoparticle (SiNPs) hybrid arrays for highly sensitive detection of biomolecules via surface-enhanced Raman spectroscopy (SERS) technique. SiNPs having 7 to 37 nm in size and with phosphorous doping varying from 1 × 1019 to 1 × 1020 cm−3 were synthesized in nonthermal plasma synthesis. SiNPs were further immobilized on glass substrates using spin-coating, followed by deposition of AgNPrs using the drop-casting method. SERS studies showed that AgNPrs/SiNPs hybrid arrays exhibit substantial amplification of fingerprint bands of rhodamine 6G (R6G) compared to bare silicon as the reference. Raman signal intensity was found to be dependent on the size of SiNPs, with the largest nanoparticles exhibiting the highest SERS enhancement. In addition, an increase in phosphorous doping concentration was found to reduce R6G peak intensities. AgNPrs/SiNPs hybrid arrays showed excellent stability over time and high spot-to-spot reproducibility as well. Moreover, hybrid arrays enabled DNA detection through intense vibrational modes of human genomic DNA, with a lower detection limit of 1.5 pg/µL; indicating that AgNPrs/SiNPs sensors can serve as a reliable and cost-effective biosensing platform for rapid and label-free analysis of biomolecules.

Silicon Passivation by Ultrathin Hafnium Oxide Layer for Photoelectrochemical Applications

Hafnium oxide (HfO2) films on silicon have the potential for application in photovoltaic devices. However, very little is known about the photoelectrochemical and protective properties of HfO2 films on Si. In this study, ultrathin films of HfO2 in the range of 15–70 nm were deposited on p-Si and Au substrates by atomic layer deposition (ALD). Grazing incidence X-ray diffraction (GI-XRD) identified the amorphous structure of the layers. Quartz crystal nanogravimetry (QCN) with Si and Au substrates indicated dynamics of electrolyte intake into the oxide film. No indications of oxide dissolution have been observed in acid (pH 3) and alkaline (pH 12) electrolytes. Mott–Schottky plots showed that the dark Si surface adjacent to the SiHfO2 interface is positively charged in an acid electrolyte and negatively charged in an alkaline electrolyte. The number of photoelectrons was determined to be much greater than the doping level of silicon. The cathodic photoactivity of the p-Si electrode protected by HfO2 films was studied with respect to the reaction of hydrogen reduction in acid and alkaline solutions. In acid solution, the film enhanced the reduction process when compared to that on the coating free electrode. The acceleration effect was explained in terms of prevention of silicon oxide formation, whose passivating capability is higher than that of hafnia films. In an alkaline electrolyte, an inhibition effect of the film was determined. Hafnia films protected Si from corrosion in this medium; however, at the same time, the film reduced electrode activity.

Optical heating of doped semiconductor nanocylinders supporting quasi-BIC modes

In the recent years, semiconductor and dielectric nanophotonic structures attracted a lot of attention for their resonant optical properties finding applications in thermal tuning and optical heating. Exciting high quality optical modes of both electric and magnetic nature in nanoresonators of high-index materials, one can effectively enhance optical absorption in such structures. Another big advantage of semiconductor materials is the ability to finely control the level of optical losses in visible and near infrared (near-IR) range through varying the doping level. In this work, we show theoretically that by moderate carrier doping of silicon via donors from group V materials one can achieve effective heating of nanoresonators. We show that by tuning the doping level of crystalline silicon supporting high quality non-radiative modes based on quasi bound states in the continuum one can achieve strong heating in near-IR under continuous wave regime illumination. We believe that our finding will pave the way for an efficient semiconductor near-IR all-optical sensors and nanoheaters.

Insights into the local structure, microstructure and ionic conductivity of silicon doped NASICON-type solid electrolyte Li1.3Al0.3Ti1.7P3O12

NASICON-type solid electrolyte Li1.3Al0.3Ti1.7P3O12 (LATP) is attractive because of the cheap raw materials, excellent air stability, and high ionic conductivity. Silicon doping is generally adopted to improve its conductivity further, but the corresponding mechanism is vacant. Herein, we synthesize the silicon doped LATP electrolyte with a simple solution-based method and systemically investigate the effects of different silicon doping level on the local structure, microstructure and ionic diffusion kinetics of the solid electrolytes. We firstly put forward the octahedral occupation of silicon in Li1.3Al0.3Ti1.7P3O12 electrolyte instead of tetrahedral sites. Silicon doping is found to be negative for the ionic transportation in grain bulk, however, the grain boundary conductivity can be increased after a small amount of silicon doping due to the modification of micro-structure, i, e., the silicon doping induces the segregation of LiTiOPO4 in the grain boundary, which can effectively suppress the abnormal growth of electrolyte grains and concomitant gas pores and cracks during sintering. As a result, the total conductivity can reach ∼10−3 S⋅cm−1 after silicon doping with this simple method. Our results demonstrate the critical importance of adjusting secondary phase on the micro-structure and ionic conductivity of electrolyte during the development of inorganic fast ionic conductors.

Optimization of the Epitaxial Growth of Undoped GaN Waveguides in GaN-Based Laser Diodes Evaluated by Photoluminescence

Non-intentionally doped c-plane GaN layers are generally employed as p-side waveguide layers in violet/blue-emitting laser diodes. The recombination and diffusion of charge carriers in the p-side GaN waveguide influence the injection efficiency of holes into the InGaN quantum wells of these devices. In this study, the non-radiative recombination and the diffusivity in the [000-1] direction for charge carriers in such GaN layers are investigated by the photoluminescence of buried InGaN quantum wells, in addition to the GaN photoluminescence. The vertical charge carrier diffusion length and the diffusion constant in GaN were determined by evaluating the intensity from InGaN quantum wells in different depths below a top GaN layer. Additionally, the intensity from the buried InGaN quantum wells was found to be more sensitive to variations in the non-radiative recombination rate in the GaN layer than the intensity from the GaN itself. The study enables conclusions to be drawn on how the growth of a p-side GaN waveguide layer has to be optimized: (1) The charge carrier diffusivity in the [000-1] direction at device operation temperature is limited by phonon scattering and can be only slightly improved by material quality. (2) The use of TMGa (trimethylgallium) instead of TEGa (triethylgallium) as a precursor for the growth of GaN lowers the background silicon doping level and is advantageous for a large hole diffusion length. (3) Small growth rates below 0.5 μm/h when using TMGa or below 0.12 μm/h when using TEGa enhance non-radiative recombination. (4) A V/III gas ratio of 2200 or more is needed for low non-radiative recombination rates in GaN.

Influence of Illumination on Porous Silicon Formed by Photo-Assisted Etching of p-Type Si with a Different Doping Level.

The influence of illumination intensity and p-type silicon doping level on the dissolution rate of Si and total current by photo-assisted etching was studied. The impact of etching duration, illumination intensity, and wafer doping level on the etching process was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), and Ultraviolet-Visible Spectroscopy (UV–Vis–NIR). The silicon dissolution rate was found to be directly proportional to the illumination intensity and inversely proportional to the wafer resistivity. High light intensity during etching treatment led to increased total current on the Si surface. It was shown that porous silicon of different thicknesses, pore diameters, and porosities can be effectively fabricated by photo-assisted etching on a Si surface without external bias or metals.

Spectral narrowing of sub-bandgap absorbance and emissivity in highly doped silicon

Doping-engineered silicon is a vertatile material, well-suitable for exploring new optical properties and applications in infrared spectral region below its bandgap. In this paper, we report on a doping-induced spectral narrowing phenomenon in silicon’s sub-bandgap absorbance and emissivity. By measuring silicon samples with doping concentration varied between <1012 cm−3 and 4.4 × 1019 cm−3, we reveal that, besides the increased amplitude in absorption and emissivity, doping induces a spectral narrowing feature in both mid-infrared absorption and emission, which indicates a trade-off existing for silicon doping level in consideration of efficiency and bandwidth. The spectral narrowing effect occurs around the plasma wavelength, where the silicon changes from dielectric-like property to metal-like property with a negative permittivity. These results are helpful in further understanding free-carrier responses in silicon, and are potentially useful for developing silicon-based materials for mid-infrared applications, such as broadband bolometric sensing, thermal energy harvesting and radiative cooling etc.

The optimization of the doping level of boron, silicon and nitrogen doped diamond film on Co-cemented tungsten carbide inserts

Boron doped, silicon doped and nitrogen doped diamond films with different doping level in gas phase are deposited on Co-cemented tungsten carbide (WC-Co) inserts using hot filament chemical vapor deposition (HFCVD) method. Trimethyl borate ((CH3O)3B), tetraethoxysilane (Si(OC2H5)4) and urea (CO(NH2)2) are dissolved in acetone to serve as boron, silicon and nitrogen precursors, respectively. The as-deposited diamond films are characterized by field emission scanning electron microscope (FESEM), Raman spectroscopy and indentation tests. The results suggested that doping source and doping level will affect the surface morphology, growth rate, quality and adhesion of diamond film. The optimized doping level to obtain diamond films deposited on WC-Co substrate for mechanical applications with well faceted crystal, low defect, low cluster structure and high adhesive strength is 5000 ppm, 10000 ppm and 10000 ppm for boron, silicon and nitrogen doping, respectively.

(Invited) Control of Silicon Doping Level By Self Limited Reactions

Precise control over dopant dose and distribution at the nanoscale is required to support further evolution in microelectronics, photovoltaics, solar fuel conversion, sensors, and quantum computation. In this contribution, an effective bottom-up technology is proposed as a promising solution to overcome the limitations of conventional doping approaches. Precise control of the amount of dopant atoms tethered on silicon substrates is presented, based on polystyrene and poly(methyl methacrylate) polymers, with controlled molar mass and featuring a narrow molar mass distribution, end-terminated with a P-containing moiety. These polymers are spin coated and subsequently end-grafted onto nondeglazed silicon substrates. P atoms were bonded to the surface during the grafting reaction, and their surface density is set by the polymer molar mass, according to the self-limiting nature of the “ grafting to” reaction. Polymeric material was removed by O2 plasma hashing without affecting the tethered P-containing moieties on the surface. Repeated cycles of polymer grafting followed by plasma hashing led to a cumulative increase, at constant steps, in the dose of atoms grafted to the silicon surface. P injection in the silicon substrate was promoted and precisely controlled by high temperature thermal treatments. Sheet resistance measurements demonstrated effective doping of silicon substrate. Although the method is demonstrated for P-containing molecules on planar deglazed and nondeglazed Si substrates, but the it can be readily implemented to other types of dopants and semiconductor substrates by using suitable combination of dopant-containing moieties and surface chemistry.

Micro-light-emitting diodes with III–nitride tunnel junction contacts grown by metalorganic chemical vapor deposition

Micro-light-emitting diodes (µLEDs) with tunnel junction (TJ) contacts were grown entirely by metalorganic chemical vapor deposition. A LED structure was grown, treated with UV ozone and hydrofluoric acid, and reloaded into the reactor for TJ regrowth. The silicon doping level of the n++-GaN TJ was varied to examine its effect on voltage. µLEDs from 2.5 × 10−5 to 0.01 mm2 in area were processed, and the voltage penalty of the TJ for the smallest µLED at 20 A/cm2 was 0.60 V relative to that for a standard LED with indium tin oxide. The peak external quantum efficiency of the TJ LED was 34%.

Precision calibration of the silicon doping level in gallium arsenide epitaxial layers

An approach to precision calibration of the silicon doping level in gallium arsenide epitaxial layers is discussed that is based on studying the dependence of the carrier density in the test GaAs layer on the silicon- source temperature using the Hall-effect and CV profiling techniques. The parameters are measured by standard or certified measuring techniques and approved measuring instruments. It is demonstrated that the use of CV profiling for controlling the carrier density in the test GaAs layer at the thorough optimization of the measuring procedure ensures the highest accuracy and reliability of doping level calibration in the epitaxial layers with a relative error of no larger than 2.5%.

Studies on the polycrystalline silicon/SiO2 stack as front surface field for IBC solar cells by two-dimensional simulations**Project supported by the National Natural Science Foundation of China (Grant Nos. 11104319, 11274346, 51202285, 61234005, 51172268, 51602340, 61274059, and 51402347), the Solar Energy Action Plan of Chinese Academy of Sciences (Grant Nos. Y1YT064001, Y1YF034001, and Y2YF014001), the Graduate and College Student’s Innovative Project

Interdigitated back contact (IBC) solar cells can achieve a very high efficiency due to its less optical losses. But IBC solar cells demand for high quality passivation of the front surface. In this paper, a polycrystalline silicon/SiO2 stack structure as front surface field to passivate the front surface of IBC solar cells is proposed. The passivation quality of this structure is investigated by two dimensional simulations. Polycrystalline silicon layer and SiO2 layer are optimized to get the best passivation quality of the IBC solar cell. Simulation results indicate that the doping level of polycrystalline silicon should be high enough to allow a very thin polycrystalline silicon layer to ensure an effective passivation and small optical losses at the same time. The thickness of SiO2 should be neither too thin nor too thick, and the optimal thickness is 1.2 nm. Furthermore, the lateral transport properties of electrons are investigated, and the simulation results indicate that a high doping level and conductivity of polycrystalline silicon can improve the lateral transportation of electrons and then the cell performance.

Specific features of current flow in α-Si : H/Si heterojunction solar cells

Specific features of the formation of dark I–V characteristics of α-Si: H/Si heterojunction solar cells are investigated taking account the ratio between silicon doping level Nd and excess concentration Δn of electron–hole pairs. It is demonstrated that, at Δn ≥ Nd, the I–V characteristic is fundamentally different from the characteristic of a classical Shockley diode due the effect of the backside surface (additional drop of the applied voltage). The results of analysis are used to describe the experimental I–V characteristics reported in studies on α-Si: H/Si heterojunction solar cells. Numerical values of the ideality factors of the dark I–V characteristics are obtained by comparing the experimental and calculated curves.

Electronic transport in highly conducting Si-doped ZnO thin films prepared by pulsed laser deposition

Highly conducting (ρ = 3.9 × 10−4 Ωcm) and transparent (83%) polycrystalline Si-doped ZnO (SiZO) thin films have been deposited onto borosilicate glass substrates by pulsed laser deposition from (ZnO)1−x(SiO2)x (0 ≤ x ≤ 0.05) ceramic targets prepared using a sol-gel technique. Along with their structural, chemical, and optical properties, the electronic transport within these SiZO samples has been investigated as a function of silicon doping level and temperature. Measurements made between 80 and 350 K reveal an almost temperature-independent carrier concentration consistent with degenerate metallic conduction in all of these samples. The temperature-dependent Hall mobility has been modeled by considering the varying contribution of grain boundary and electron-phonon scattering in samples with different nominal silicon concentrations.

Silicon Waveguides at the Mid-Infrared

In this paper, we propose a detailed study of various novel waveguides made using doped silicon at the mid-infrared (MIR) range. These waveguides support a plasmonic-like mode with nanoscale confinement in the MIR. We also demonstrate a simple mechanism for tuning the plasma resonance through controlling the doping level of silicon. Moreover, the dispersion characteristics of the doped silicon devices are analyzed for different applications at the MIR region. We also investigated various phenomenon such as negative dispersion, which can be utilized for slow light and metamaterial applications, and epsilon-near-zero characteristics that can be used for extraordinary transmission. The MIR dispersion is studied thoroughly for the slot structure and the rectangular shell structure. The potential for biological and environmental sensing for the aforementioned structures is investigated as well. In addition, we demonstrated the use of the waveguide as a slow light medium; this was facilitated as the dispersion relations reached giant values in the order of $10^{5}$ at the resonance.

P +-Si/nano-SiO2/n +-Si capacitor-based tunnel diode with negative differential resistance and a quartz resonator

To demonstrate the extending functionality of the simplest MOS (metal-oxide-semiconductor) capacitor, a structure with a p+-Si/nano-SiO2 heterojunction in which strongly degenerate n+-Si is used instead of a metal electrode is considered. As a result, a tunnel diode with negative differential resistance and a quartz resonator is obtained. Its electrical characteristics are superior to those of the corresponding Esaki diode and are controlled not only by the Silicon doping level, but also by the SiO2 thickness.