Doped Silicon Nanowires Research Articles

Solid-Liquid-Solid Growth of Doped Silicon Nanowires for High-Performance Lithium-Ion Battery Anode

Silicon nanowires (SiNWs) have great potential in electronic devices, sensors, energy storage, and conversion devices. Despite various ways to synthesize SiNWs, however, the growth of SiNWs directly from stable, abundant, sustainable silica sources has yet to be achieved. Herein, we report a modified alumino-reduction process of the silica to produce tin (Sn)-doped SiNWs that can be initiated at low temperature (250 °C) based on a solid-liquid-solid growth mechanism in analogy to the well-known vapor-liquid-solid (VLS). In this growth process, the reduced silicon atoms migrate freely in the molten salt and alloy with pre-reduced Sn. The supersaturation of silicon in the Sn-Si alloy leads to the precipitation of single-crystal SiNWs. The prepared SiNWs are of excellent crystallinity and doped with high non-equilibrium concentration (~3.0at.%) of Sn. This process with the solid-liquid-solid mechanism can also be extended to produce other group IV elements-based nanowires such as germanium. In addition, the prepared Sn-doped SiNWs as the anode material in lithium-ion batteries exhibit excellent performance with a high initial Coulombic efficiency of 85.4%, and a substantial reversible capacity of 1133 mAh g-1 even after 500 cycles at 4Ag-1. By utilizing the solid-liquid-solid mechanism, this modified alumino-reduction process offers a novel route for synthesizing doped SiNWs, holding promise for diverse applications.

Urea adsorption and detection using silicon nanowires doped with B, Al, C, Ge, N, and P: A DFT investigation

Urea can serve as a biomarker for the detection of various illnesses, including renal and hepatic failure. Consequently, the development of novel devices and materials capable of adsorbing and identifying urea is a crucial objective for the scientific community. This study theoretically investigates the adsorption and detection capabilities of doped silicon nanowires (SiNWs) for urea using Density Functional Theory (DFT). Doping involves substituting a silicon atom on the surface with a dopant atom; B, Al, C, Ge, N, and P were employed for this purpose. This study presents an innovative method for enhancing urea adsorption and detection by doping SiNWs with group XIII elements, specifically aluminum and boron atoms. The results indicate that this doping significantly improves urea adsorption on SiNWs compared to undoped SiNWs. Notable changes in the bandgaps and work functions of the doped nanowires following urea adsorption suggest their potential use as diagnostic tools for uremia.

Nonvolatile Phase-Only Transmissive Spatial Light Modulator with Electrical Addressability of Individual Pixels.

Active metasurfaces with tunable subwavelength-scale nanoscatterers are promising platforms for high-performance spatial light modulators (SLMs). Among the tuning methods, phase-change materials (PCMs) are attractive because of their nonvolatile, threshold-driven, and drastic optical modulation, rendering zero-static power, crosstalk immunity, and compact pixels. However, current electrically controlled PCM-based metasurfaces are limited to global amplitude modulation, which is insufficient for SLMs. Here, an individual-pixel addressable, transmissive metasurface is experimentally demonstrated using the low-loss PCM Sb2Se3 and doped silicon nanowire heaters. The nanowires simultaneously form a diatomic metasurface, supporting a high-quality-factor (∼406) quasi-bound-state-in-the-continuum mode. A global phase-only modulation of ∼0.25π (∼0.2π) in simulation (experiment) is achieved, showing ten times enhancement. A 2π phase shift is further obtained using a guided-mode resonance with enhanced light-Sb2Se3 interaction. Finally, individual-pixel addressability and SLM functionality are demonstrated through deterministic multilevel switching (ten levels) and tunable far-field beam shaping. Our work presents zero-static power transmissive phase-only SLMs, enabled by electrically controlled low-loss PCMs and individual meta-molecule addressable metasurfaces.

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%.

Modulation Doping of Silicon Nanowires to Tune the Contact Properties of Nano‐Scale Schottky Barriers

AbstractDoping silicon on the nanoscale by the intentional introduction of impurities into the intrinsic semiconductor suffers from effects such as dopant deactivation, random dopant fluctuations, out‐diffusion, and mobility degradation. This paper presents the first experimental proof that doping of silicon nanowires can also be achieved via the purposeful addition of aluminium‐induced acceptor states to the SiO2 shell around a silicon nanowire channel. It is shown that modulation doping lowers the overall resistance of silicon nanowires with nickel silicide Schottky contacts by up to six orders of magnitude. The effect is consistently observed for various channel geometries and systematically studied as a function of Al2O3 content during fabrication. The transfer length method is used to separate the effects on the channel conductivity from that on the barriers. A silicon resistivity is achieved as low as 0.04–0.06 Ω ·cm in the nominal undoped material. In addition, the specific contact resistivity is also strongly influenced by the modulation doping and reduced down to 3.5E‐7 Ω · cm2, which relates to lowering the effective Schottky barrier to 0.09 eV. This alternative doping method has the potential to overcome the issues associated with doping and contact formation on the nanoscale.

Modification of Silicon Nanostructures by Cold Atmospheric Pressure Plasma Jets

Cold atmospheric plasma (CAP) jets with helium (He) and argon (Ar) plasma-forming gases were used to modify the structure, photoluminescence (PL), and electrical properties of arrays of silicon nanowires (SiNWs) with initial cross-section sizes of the order of 100 nm and length of about 7‒8 microns. The CAP source consisted of a 30 kHz voltage generator with a full power up to 5 W and the CAP treatment for 1‒5 min resulted in spattering of SiNWs’ tips followed by redeposition of silicon atoms. An increase of the silicon oxide phase and a decrease of the PL intensity were observed in the plasma processed SiNW arrays. A decrease of the free hole concentration and an increase in the free electron density were revealed in heavily boron and phosphorous doped SiNWs, respectively, as it was monitored by means of the Raman spectroscopy, considering a coupling of the light scattering by phonon and free charge carriers (Fano effect) in SiNWs. The obtained results demonstrate that the CAP treatment can be used to change the length, sharpness, luminescence intensity, and electrical properties of silicon nanowires for possible applications in optoelectronics and sensorics.

First-principles study of room-temperature ferromagnetism in transition-metal doped H-SiNWs.

Hydrogen-saturated silicon nanowires (H-SiNWs) are the most attractive materials for nanoelectronics due to their special tunable electronic properties. The incorporation of magnetism in H-SiNWs can be extremely beneficial for a wide range of emerging spintronic devices, which can offer a more effective way to control spin. Here, we investigate the energetic stability, electronic properties, and magnetic properties of transition metal (TM), i.e., Fe and Mn doped Hydrogen-saturated silicon nanowires (TM:H-SiNWs) that have a diameter of 1 nm directed in (100), (110), and (111) facets using spin-polarized density functional theory (DFT). The calculations showed that the TM-doped H-SiNWs (TM:H-SiNWs) convince the electronic and magnetic alterations of H-SiNWs semiconductors. It can be ascertained that the total magnetization of the studied configurations is contributed by the hybridization between a localized p orbital of Si and a d orbital of the TM atoms. In addition, we report the Curie temperature of the TM:H-SiNWs using a mean-field approximation and a Monte Carlo simulation based on the Ising model. We obtain the above room temperature ferromagnetism in the (100) and (111) direction-oriented Mn:H-SiNWs. This study provides an in-depth knowledge of the properties of TM-doped H-SiNWs and can be used as a reference in silicon-based spintronic devices.

Sensitive and Specific Detection of Estrogens Featuring Doped Silicon Nanowire Arrays.

Estrogens and estrogen-mimicking compounds in the aquatic environment are known to cause negative impacts to both ecosystems and human health. In this initial proof-of-principle study, we developed a novel vertically oriented silicon nanowire (vSiNW) array-based biosensor for low-cost, highly sensitive and selective detection of estrogens. The vSiNW arrays were formed using an inexpensive and scalable metal-assisted chemical etching (MACE) process. A vSiNW array-based p-n junction diode (vSiNW-diode) transducer design for the biosensor was used and functionalized via 3-aminopropyltriethoxysilane (APTES)-based silane chemistry to bond estrogen receptor-alpha (ER-α) to the surface of the vSiNWs. Following receptor conjugation, the biosensors were exposed to increasing concentrations of estradiol (E2), resulting in a well-calibrated sensor response (R 2 ≥ 0.84, 1-100 ng/mL concentration range). Fluorescence measurements quantified the distribution of estrogen receptors across the vSiNW array compared to planar Si, indicating an average of 7 times higher receptor presence on the vSiNW array surface. We tested the biosensor's target selectivity by comparing it to another estrogen (estrone [E1]) and an androgen (testosterone), where we measured a high positive electrical biosensor response after E1 exposure and a minimal response after testosterone. The regeneration capacity of the biosensor was tested following three successive rinses with phosphate buffer solution (PBS) between hormone exposure. Traditional horizontally oriented Si NW field effect transistor (hSiNW-FET)-based biosensors report electrical current changes at the nanoampere (nA) level that require bulky and expensive measurement equipment making them unsuitable for field measurements, whereas the reported vSiNW-diode biosensor exhibits current changes in the microampere (μA) range, demonstrating up to 100-fold electrical signal amplification, thus enabling sensor signal measurement using inexpensive electronics. The highly sensitive and specific vSiNW-diode biosensor developed here will enable the creation of low-cost, portable, field-deployable biosensors that can detect estrogenic compounds in waterways in real-time.

Analysis of synthesized doped vertical silicon nanowire arrays for effective sensing of nitrogen dioxide: As gas sensors

In the present study, the controllable fabrication of silicon nanowires (Si NWs) with vertical alignment was accomplished using metal assisted chemical etching (MACE). The different characteristics, such as structural, morphological, chemical, optical, and dielectric properties were analyzed using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), and LCR [inductance (L), capacitance (C), and resistance (R)] meter (volume of the gas-sensing chamber is 650 mm3). It was revealed from the morphological study i.e., from the FESEM that p-type Si NWs are smaller in size than n-type Si NWs which is attributable to the energy band gap. The optical band gap (Eg) is observed to increase from 1.64 to 1.89 eV with the decreasing of the crystallite size and the optical reflection spectra of the Si NWs show a shift toward a lower wavelength (blue shift). Moreover, Raman spectra verified the red-shifted, asymmetrically broadened Raman line-shapes, which provides information about the size confinement effect in Si NWs. The MACE approach is excellent for synthesizing nanowire structures for use in gas-sensing applications due to its flexibility. The sensitivity of synthesized Si NWs was tested for NO2 gas. The sensor method is unique based on the testing of the device in the presence of a test gas because the use of the gas-sensing setup has the potential to measure the change in resistance by varying frequency, temperature, and time.

Performance Assessment and Optimization of Vertical Nanowire TFET for Biosensor Application

This paper reports the performance assessment of vertical silicon nanowire TFET (V-siNWTFET) design for biosensor applications using dielectric-modulation and gate underlap technique. The sensitivity of the V-siNWTFET is recognizing by immobilizing the different biological molecules such as lipids, biotin, uricase, protein, Gox, streptavidin, uriease, zein etc. in the cavity region which is created under the gate electrode and source oxide. The performance analysis is observed by varying the relative permittivity of the different biomolecules and analyzes the parametric variation both for neutral and charged biomolecules. The sensitivity of the biosensor has been detecting in the terms of drain current (ID), threshold voltage (VTH), subthreshold slope (SS), transconductance (gm), and ION/IOFF ratio. The proposed device structure has capable to reduce the leakage currents and high sensitivity biosensor design in the nanoscale regimes. The obtained best optimum parameters of the proposed devices are ION (1.37E−08 A/µm), IOFF (9.44E−19 A/µm), SS (29.97 mV/dec) and ION/IOFF (4.29E + 10) ratio with gate work-function (ϕgate = 4.8 eV) and uniformly doped (1 × 10–19 cm−3) silicon nanowire at drain to source voltage (VDS = 1.0 V). The higher sensitivity of the proposed V-siNWTFET for Biosensor is observed for Zein biomolecules (K = 5).

Investigation of the discharging behaviors of different doped silicon nanowires in alkaline Si-air batteries

Compared with metal-air batteries, Si-air batteries have advantages on gravimetric/volumetric capacity and safety. This novel battery using flat Si wafer as anode has been preliminarily researched in recent ten years. In this work, Si nanowires (NWs) have been fabricated on p < 100 > and n < 100 > Si wafers and their discharging behaviors under various operating conditions have been systematically analyzed compared with flat Si wafer anodes. Si NWs anodes universally exhibit longer discharge times than flat Si wafer anodes because of their larger specific surface areas and superior resistance to the passivation caused by SiO2 deposition. It is also demonstrated that a KOH electrolyte concentration of 1.9 M is the lowest threshold for the p < 100 > Si anode at a current density of 0.03 mA/cm2, and the p < 100 > Si anode can discharge for more than 400 h. Furthermore, n < 100 > Si NWs anodes performed best with a discharge time of more than 500 h at higher current density of 0.05 mA/cm2 with an electrolyte concentration of 6 M. This work can aid in understanding the electrochemical properties of silicon anodes with different configurations and doping types in Si-air batteries and provide direction for the operation of Si-air batteries at appropriate conditions.

The effect of dopant on light trapping characteristics in random silicon nanowires for solar cell applications

The Light management is a fundamental study to improve the solar cell and photoelectrical devices conversion efficiency. Here, the spectral responses of reflection and absorption characteristics of random silicon nanowires (Si-NWs) arrays of different lengths and doping type has been investigated. The Si-NWs have been synthesized by metal induced etching (MIE) approach have dimensions of Sub-wavelength regime. These Si-NWs arrays show efficient light trapping and low reflectance than bare Si due to suppression of Fresnel reflection substantially over a wide spectral range. The comparative study of light trapping in Si-NWs, fabrication by using n-type and p-type Si wafer have been explored to add new dimension in the field of photovoltaic application. Here, diffuse reflection spectra have been used to analyzed the light-scattering properties of Si-NWs, which reveal that the diffuse scattering decreases as the pore depth increases. The field distribution of Si-NWs is simulated using finite differential time domain (FDTD) method, results shows that reflectance could be modified due to light absorption driven by multiple scattering inside the structure reaching high values of apparent absorbance. Current-voltage (I–V) curves have been measured under illumination at standard testing conditions (STC), i.e., 300 K, 1000 W/m2 and 1.5 a.m. global by using solar simulator. These measurement studies indicate that dopant (n-type and p-type) have been effectively influenced the photovoltaic parameters. I–V curve indicated that the power conversion efficiency (PCE) of n-type and p-type doped Si-NWs exhibited PCE of 3.94% and 4.01% respectively.

Silicon nanowires as acetone-adsorptive media for diabetes diagnosis

Early detection of diabetes, a worldwide health issue, is key for its successful treatment. Acetone is a marker of diabetes, and efficient, non-invasive detection can be achieved with the use of nanotechnology. In this paper we investigate the effect of acetone adsorption on the electronic properties of silicon nanowires (SiNWs) by means of density functional theory. We considered hydrogenated SiNWs grown along the [111] bulk Si axis, with group-III impurities (B, Al, Ga), for which both surface substitutional doping and functionalizing schemes are considered. We present an analysis of the adsorption configuration, energetics, and electronic properties of the undoped and doped SiNWs. Upon acetone adsorption, the SiNW without impurities becomes an n-type semiconductor, while most substituted/functionalized cases have their HOMO-LUMO gap tuned, which could be harnessed in optical sensors. Acetone is always chemisorbed, although for the case without impurities, and the Al- and Ga-functionalization schemes, the chemisorption is very weak. These nanostructures could be used for acetone capture and detection, which could lead to applications in the medical treatment of diabetes.

Silicon Suboxides as Driving Force for Efficient Light-Enhanced Hydrogen Generation on Silicon Nanowires.

Efficient light-stimulated hydrogen generation from top-down produced highly doped n-type silicon nanowires (SiNWs) with silver nanoparticles (AgNPs) in water-containing medium under white light irradiation is reported. It is observed that SiNWs with AgNPs generate at least 2.5 times more hydrogen than SiNWs without AgNPs. The authors' results, based on vibrational, UV-vis, and X-ray spectroscopy studies, strongly suggest that the sidewalls of the SiNWs are covered by silicon suboxides, by up to a thickness of 120nm, with wide bandgap semiconductor properties that are similar to those of titanium dioxide and remain stable during hydrogen evolution in a water-containing medium for at least 3h of irradiation. Based on synchrotron studies, it is found that the increase in the silicon bandgap is related to the energetically beneficial position of the valence band in nanostructured silicon, which renders these promising structures for efficient hydrogen generation.

Compact Modeling of Schottky Gate-all-around Silicon Nanowire Transistors with Halo Doping

A physics-based compact model for halo doped Silicon Nanowire Transistor with Schottky-barrier (SB) contact at the source/drain (S/D) junctions is developedconsidering the quasi-2D surface-potential solution. The halo implant is considered only at the source side to avoid hot electron effects in the high field drain region. The surface potential and electric field expressions are derived using a systematic approach. The impact of a single halo at the source is analyzed using the energy band model. The analysis shows that the halo increases the electron energy at the source side and suppresses the short channel effects. Moreover, high doping of halo decreases the tunneling barrier width, thereby increasing the ON-state current. Physics-based modeling of the surface potential at the halo boundary has ensured that the model preserves accuracy and continuity.

Impact of Device Parameter Variation on the Electrical Characteristic of N-type Junctionless Nanowire Transistor with High-k Dielectrics

Metallurgical junction and thermal budget are serious constraints in scaling and performance of conventional metal-oxide-semiconductor field-effect transistor (MOSFET). To overcome this problem, junctionless nanowire field-effect transistor (JLNWFET) was introduced. In this paper, we investigate the impact of device parameter variation on the performance of n-type JLNWFET with high-k dielectrics. The electrical characteristic of JLNWFET and the inversion-mode transistor of different gate length (L G ) and nanowire diameter (d NW ) was compared and analyzed. Different high-k dielectrics were used to get an optimum device structure of JLNWFET. The device was simulated using SDE Tool of Sentaurus TCAD and the I-V characteristics were simulated using Sdevice Tools. Lombardi mobility model and Philips unified mobility model were applied to define its electric field and doping dependent mobility degradation. A thin-film heavily doped silicon nanowire with a gate electrode that controls the flow of current between the source and drain was used. The proposed JLNWFET exhibits high ON-state current (I ON ) due to the high doping concentration (N D ) of 1 x 10 19 cm -3 which leads to the improved ON-state to OFF-state current ratio (I ON /I OFF ) of about 10% than the inversion-mode device for a L G of 7 nm and the silicon d NW of 6 nm. Electrical characteristics such are drain induced barrier lowering (DIBL) and subthreshold slope (SS) were extracted which leads to low leakage current as well as a high I ON /I OFF ratio. The performance was improved by introducing silicon dioxide (SiO 2 ) with high-k dielectric materials, hafnium oxide (HfO 2 ) and silicon nitrate (Si 3 N 4 ). It was found that JLNWFET with HfO 2 exhibits better electrical characteristics and performance.

Impact of Device Parameter Variation on the Electrical Characteristic of N-type Junctionless Nanowire Transistor with High-k Dielectrics

Metallurgical junction and thermal budget are serious constraints in scaling and performance of conventional metal-oxide-semiconductor field-effect transistor (MOSFET). To overcome this problem, junctionless nanowire field-effect transistor (JLNWFET) was introduced. In this paper, we investigate the impact of device parameter variation on the performance of n-type JLNWFET with high-k dielectrics. The electrical characteristic of JLNWFET and the inversion-mode transistor of different gate length (L G ) and nanowire diameter (d NW ) was compared and analyzed. Different high-k dielectrics were used to get an optimum device structure of JLNWFET. The device was simulated using SDE Tool of Sentaurus TCAD and the I-V characteristics were simulated using Sdevice Tools. Lombardi mobility model and Philips unified mobility model were applied to define its electric field and doping dependent mobility degradation. A thin-film heavily doped silicon nanowire with a gate electrode that controls the flow of current between the source and drain was used. The proposed JLNWFET exhibits high ON-state current (I ON ) due to the high doping concentration (N D ) of 1 x 10 19 cm -3 which leads to the improved ON-state to OFF-state current ratio (I ON /I OFF ) of about 10% than the inversion-mode device for a L G of 7 nm and the silicon d NW of 6 nm. Electrical characteristics such are drain induced barrier lowering (DIBL) and subthreshold slope (SS) were extracted which leads to low leakage current as well as a high I ON /I OFF ratio. The performance was improved by introducing silicon dioxide (SiO 2 ) with high-k dielectric materials, hafnium oxide (HfO 2 ) and silicon nitrate (Si 3 N 4 ). It was found that JLNWFET with HfO 2 exhibits better electrical characteristics and performance.

Ab initio studies of the optoelectronic structure of undoped and doped silicon nanocrystals and nanowires: the role of size, passivation, symmetry and phase.

Silicon nanocrystals and nanowires have been extensively studied because of their novel properties and their applications in electronic, optoelectronic, photovoltaic, thermoelectric and biological devices. Here we discuss results from ab initio calculations for undoped and doped Si nanocrystals and nanowires, showing how theory can aid and improve comprehension of the structural, electronic and optical properties of these systems.

Photoluminescence origin of lightly doped silicon nanowires treated with acid vapor etching

In this work, we carry out a comprehensive photoluminescence (PL) study to elucidate the origin of light emission from porous silicon nanowires (pSiNWs). SiNWs were first grooved in lightly doped Si wafer by silver assisted chemical etching, and then treated with an acid vapor emanating from HF/HNO3 aqueous solution heated at 60 °C. Scanning and transmission electron microscopies were used to investigate the effect of the acid vapor etching on morphological properties of SiNWs. The as prepared pSiNWs exhibited a strong room temperature PL emission centered at 1.93 eV. An increase of the PL intensity was observed with the increase of HNO3 in the acid solution. By varying the laser excitation density from 60 to 300 W/cm2, we shed the light on the radiative recombination modes occurring within the Si nanocrystals (SiNCs) generated along the pSiNWs. We study as well the temperature-dependent PL of the pSiNWs in the range 10 to 300 K. Based on both laser excitation density and temperature-dependent PL, we propose a multilevel transition scheme resuming the PL origin taking into account the size distribution, shape and surface states of the SiNCs trimming the wire sidewalls.

Logic “AND” and “OR” realized in a single intelligent three dimension transistor

In this letter, a more intelligent three dimension transistor than a mere switching device is developed. The phosphorus doped silicon nanowire channel, SiO2 dielectric and three separated gates are applied for demonstrations with a gate length of 7 nm. The transistor is called “LIU MOSFET” due to its less interconnected unit characteristic. Logic “AND” and “OR” are achieved when the control gate is set to −3 V and 3 V, respectively. The logic function can be altered by external signals without any changes in the hardware. The demonstrated device is significant to the development of future integrated circuits.