Control of Silicon Nanowires Crystallinity using Metal Assisted Chemical Etching of Silicon and Porous Silicon Substrate (original) (raw)
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Nanotechnology, 2015
A systematic method to control the porosity of silicon nanowires is presented. This method is based on metal-assisted chemical etching (MACE) and takes advantage of an HF/H2O2 etching solution and a silver catalyst in the form of a thin patterned film deposited on a doped silicon wafer. It is found that the porosity of the etched nanowires can be controlled by the doping level of the wafer. For low doping concentrations, the wires are primarily crystalline and surrounded by only a very thin layer of porous silicon (pSi) layer, while for highly doped silicon, they are porous in their entire volume. We performed a series of controlled experiments to conclude that there exists a well-defined critical doping concentration separating the crystalline and porous regimes. Furthermore, transmission electron microscopy investigations showed that the pSi has also a crystalline morphology on a length scale smaller than the pore size, determined from positron annihilation lifetime spectroscopy t...
ACS Omega, 2017
We demonstrate controlled fabrication of porous Si (PS) and vertically aligned silicon nanowires array starting from bulk silicon wafer by simple chemical etching method, and the underlying mechanism of nanostructure formation is presented. Silicon-oxidation rate and the electron-scavenging rate from metal catalysis play a vital role in determining the morphology of Si nanostructures. The size of Ag catalyst is found to influence the Si oxidation rate. Tunable morphologies from irregular porous to regular nanowire structure could be tailored by controlling the size of Ag nanoparticles and H 2 O 2 concentration. Ag nanoparticles of size around 30 nm resulted in irregular porous structures, whereas discontinuous Ag film yielded nanowire structures. The depth of the porous Si structures and the aspect ratio of Si nanowires depend on H 2 O 2 concentration. For a fixed etching time, the depth of the porous structures increases on increasing the H 2 O 2 concentration. By varying the H 2 O 2 concentration, the surface porosity and aspect ratio of the nanowires were controlled. Controlling the Ag catalyst size critically affects the morphology of the etched Si nanostructures. H 2 O 2 concentration decides the degree of porosity of porous silicon, dimensions and surface porosity of silicon nanowires, and etch depth. The mechanisms of the size-and H 2 O 2-concentration-dependent dissociation of Ag and the formation of porous silicon and silicon nanowire are described in detail.
Journal of Nanoelectronics and Optoelectronics, 2012
Silicon nanowires (SiNWs) formed by metal(silver)-assisted chemical etching of lowly boron-doped (100)-oriented single crystalline silicon substrates in hydrofluoric acid solutions are investigated by means of the electron microscopy and optical spectroscopy (absorption and reflection measurements, photoluminescence spectroscopy and imaging). The growth rate of SiNWs is found to depend nonlinearly on the time of etching. The formed SiNW arrays demonstrate a strong decrease of the total reflectance below 1% in the full visible and near infrared region between 300 and 1000 nm and the samples show the similar optical properties as "Black Silicon," which can be used as antireflection coating in photovoltaic applications. The prepared SiNWs exhibit efficient photoluminescence in the spectral region of 600-1000 nm and it is explained by the radiative recombination of excitons confined within nanostructured sidewall of SiNWs. The excitons luminescence is also observed in aqueous suspensions of SiNWs, whose application in bio-imaging is demonstrated in vitro.
Nanoscale Research Letters, 2014
In this work, we use a two-step metal-assisted chemical etching method to produce films of silicon nanowires shaped in micrograins from metallurgical-grade polycrystalline silicon powder. The first step is an electroless plating process where the powder was dipped for few minutes in an aqueous solution of silver nitrite and hydrofluoric acid to permit Ag plating of the Si micrograins. During the second step, corresponding to silicon dissolution, we add a small quantity of hydrogen peroxide to the plating solution and we leave the samples to be etched for three various duration (30, 60, and 90 min). We try elucidating the mechanisms leading to the formation of silver clusters and silicon nanowires obtained at the end of the silver plating step and the silver-assisted silicon dissolution step, respectively. Scanning electron microscopy (SEM) micrographs revealed that the processed Si micrograins were covered with densely packed films of self-organized silicon nanowires. Some of these nanowires stand vertically, and some others tilt to the silicon micrograin facets. The thickness of the nanowire films increases from 0.2 to 10 μm with increasing etching time. Based on SEM characterizations, laser scattering estimations, X-ray diffraction (XRD) patterns, and Raman spectroscopy, we present a correlative study dealing with the effect of the silver-assisted etching process on the morphological and structural properties of the processed silicon nanowire films.
Investigation of Silicon Nanowires Produced by Metal-Assisted Chemical Etching Method
IOP Conference Series: Materials Science and Engineering, 2020
Silicon nanowires (SiNWs) have a strong potential in many fields. The investigation of fabrication methods for SiNWs has attracted much attention in semiconductor applications. This paper proposes a metal-assisted chemical etching (MACE) method as a low-cost and simple method for fabrication of SiNWs. This method is based on the electroless metal deposition (EMD) principle. We have studied the conditions of MACE method for fabrication of SiNWs on (100) p-type silicon wafer. A 0.005 AgNO3 and 4.8 M HF solution is used for metal-assisted depositing of the silver nanodots. The etching process is achieved by etchant solution consisting of 4.8 M HF and different concentrations of H2O2. The effect of etching parameters, such as etching time, H2O2 concentration and the dipping time, are investigated. Taguchi with L9 orthogonal array is used by software package MINITAB 17 for designing the experiments. The results of scanning electron microscopy (SEM) observations shows the formation of the...
Structural and optical characteristics of silicon nanowires fabricated by wet chemical etching
Chemical Physics Letters, 2011
Array-ordered silicon nanowires (SiNWs) were fabricated directly on p-Si substrate by wet chemical etching. The as-prepared SiNWs apparently were composed of a single-crystalline Si core embedded in an amorphous SiO 2 shell ($5 nm). Raman spectra indicated that the surface of as-prepared SiNWs contained a collection of smaller Si crystalline nanograins. The characteristic peaks induced by Si nanograins were observed in the Raman and photoluminescence (PL) spectra due to the quantum confinement effect. The study revealed that the array-ordered SiNWs would have a great potential of application in nanoscale electric and optoelectronic devices by controlling the fabrication processes.
Synthesis and Characterization of Silicon Nanowires by Electroless Etching
Journal of Materials Engineering and Performance, 2018
Synthesis of silicon nanocrystals embedded in a dielectric matrix has attracted considerable interest in third-generation photovoltaics. Till date, significant work has been done on synthesizing and characterization of Si nanocrystals embedded in oxide and nitride dielectric matrices. Recently, silicon carbide based matrices have gathered much attention because of its comparatively lower band gap (2.5 eV) as compared to Si 3 N 4 (5.3 eV) and SiO 2 (9 eV) thereby promising a better electrical conductivity. In this work, Si-rich SiC films are synthesized and investigated for possible formation of Si Quantum Dots (QD) within the matrix. A comparative analysis of film growth using variant approaches in sputtering techniques, and PECVD technique are carried out. The effect of annealing at different temperatures and ambience in favouring the Si QD formation, structural and optical properties of the film are studied.This work paves way to analyse the possibility of these nanometric films for future photovoltaic applications.
Hybrid Silicon Nanowires for Solar Cell Applications
Emerging Solar Energy Materials
The global human population has been growing by around 1.1% per year; such growth rate will lead the humanity to cross the 10 billion-people threshold by the end of the first half of this century. Such increase is already putting a huge strain on the nonrenewable sources of energy like fossil fuel, which will run out and come to an end in few decades. Due to these social and economic trends, renewable sources of energy, such as solar cells, have attracted a huge interest as the ultimate alternative to solve humanity's problems. Among several emerging materials, porous silicon nanowires (PSiNWs) become an active research subject nowadays in photovoltaic application mainly due to its good light trapping effect. The etched nanowires obtained by using metal-assisted chemical etching method (MACE) can reach a low reflection in the visible range. Recently, hybrid silicon nanowires/organic solar cells have been studied for low-cost Si photovoltaic devices because the Schottky junction between the Si and organic material can be formed by solution processes at low temperature. In this chapter, we will present the synthesis of SiNWs and the last progress on the fabrication of hybrid solar cells using various organic semiconductors.