Structural and optical characteristics of silicon nanowires fabricated by wet chemical etching (original) (raw)
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Photoluminescence and Raman Scattering in Arrays of Silicon Nanowires
Journal of Nanoelectronics and Optoelectronics, 2011
Arrays of silicon (Si) nanowires with mean diameters of about 50-100 nm formed by wet-chemical etching of crystalline silicon wafers with low and high doping levels were investigated by means of photoluminescence and Raman spectroscopy. The photoluminescence bands in the spectral ranges of 650-900 nm and about 1100 nm were detected and explained by the radiative recombination of excitons confined in Si nanocrystals on the surface of Si nanowires and by the interband photoluminescence in the volume of Si nanowires, respectively. The intensities of the band-gap related photoluminescence and Raman scattering under excitation at 1064 nm were significantly larger for the Si nanowire samples in comparison with that for the crystalline Si substrates. This fact is explained by strong scattering of the excitation light, which results in partial light trapping in silicon nanowire arrays. The doping level and surface orientation of the substrate were found to influence the photoluminescence and Raman scattering in Si nanowire arrays.
Micro-Raman scattering and electron field emission characteristics of silicon nanowires (SiNWs) synthesized by metal assisted chemical etching (MACE) are investigated. Scanning electron microscopy images reveal the growth of well aligned vertical SiNWs. Raman shift and size relation from bond-polarizability model has been used to calculate exact confinement sizes in SiNWs. The Si optical phonon peak for SiNWs showed a downshift and an asymmetric broadening with decreasing diameter of the SiNWs due to quantum connement of optical phonons. The field emission characteristics of these SiNWs are studied based by carrying out currentvoltage measurements followed by a theoretical analysis using FowlerNordheim equation. The electron field emission increased with decreasing diameter of SiNWs. Field emission from these SiNWs exhibits signicant enhancement in turn-on eld and total emission current with decreasing nanowire size. The reported results in the current study indicate that MACE is a simple technique to prepare well-aligned SiNWs with potentials for applications in field emission devices.
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.
Room temperature growth of wafer-scale silicon nanowire arrays and their Raman characteristics
Journal of Nanoparticle Research, 2010
We report a simple, inexpensive, and rapid process for large area growth of vertically aligned crystalline silicon nanowires (SiNWs) of diameter 40–200 nm and variable length directly on p-type (100) silicon substrate. The process is based on Ag-induced selective etching of silicon wafers wherein the growth of SiNWs was carried out using the aqueous HF solution containing Ag+ ions at room temperature in a Teflon vessel. Effect of etching time has been investigated to understand the evolution of SiNW arrays. It has been found that the length of SiNWs has a linear dependence on the etching time for small to moderate periods (0–2 h). However, etching rate decreases slowly for long etching times (>2 h). Scanning electron microscopy was used to study the morphology of the SiNW arrays. Structural and compositional analysis was carried out using Raman spectroscopy and high-resolution transmission electron microscopy equipped with energy dispersive X-ray spectroscopy. Orders of magnitude intensity enhancement along with a small downshift and broadening in the first-order Raman peak of SiNW arrays was observed in comparison to the bulk crystalline silicon.
Optical Characterization of Luminescent Silicon Nanowires
Journal of the Korean Physical Society, 2019
Visible photoluminescence (PL) at room temperature from silicon nanowires (Si NWs) prepared by using the metal-assisted chemical-etching (MACE) technique is reported. The morphology and the luminescence properties of Si NWs are characterized by using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), and luminescence spectroscopy. TEM images of the luminescent Si NWs reveal that the surfaces of the Si NWs are very rough, with a few nano-sized silicon particles being attached to the Si NWs. Luminescent Si NWs are optically characterized by PL and Raman measurements. Temperature-dependent PL measurements are measured at temperatures from 5 K to room temperature to determine the origin of the PL. The PL intensity decreases and the wavelength of the PL is blue-shifted as the temperature is increased. The Raman spectra of luminescent Si NWs reveal quantum confinement of the Si NWs.
Raman photoluminescence spectra of silicon nanowires synthesized by a vapor phase transport method
Advances in Natural Sciences: Nanoscience and Nanotechnology, 2011
Silicon nanowires were successfully synthesized by a thermal evaporation method. We have observed a strong and broad emission band centered at 670 nm, which is attributed to the quantum confinement effect related to Si nanostructures embedded in the complex SiO x matrix. By fitting an experimental Raman spectrum, we confirm that the as-received wires possess crystalline silicon cores whose sizes were around 5 nm. Furthermore, the abnormal dependence of integral photoluminescence intensity on measured temperature was investigated.
Nanotechnology, 2012
We present a novel approach for the direct synthesis of ultrathin Si nanowires (NWs) exhibiting room temperature light emission. The synthesis is based on a wet etching process assisted by a metal thin film. The thickness-dependent morphology of the metal layer produces uncovered nanometer-size regions which act as precursor sites for NW formation. The process is cheap, fast, maskless and compatible with Si technology. Very dense arrays of long (several micrometers) and small (diameter of 5-9 nm) NWs have been synthesized. An efficient room temperature luminescence, visible with the naked eye, is observed when NWs are optically excited, exhibiting a blue-shift with decreasing NW size in agreement with quantum confinement effects. A prototype device based on Si NWs has been fabricated showing a strong and stable electroluminescence at low voltages. The relevance and the perspectives of the reported results are discussed, opening the route toward novel applications of Si NWs.
Materials Science in Semiconductor Processing, 2019
This paper reports the fabrication of silicon nanowires (SiNWs) by silver (Ag) metal-assisted chemical etching (MACE) method. N-type Si (100) wafers, doped with phosphorus with the resistivity from 1 ÷ 10 Ω×cm, were selected for sample preparation. Ag particles of about 30 nm in diameter, which were used as the catalytic metal, were aggregated on the surface of the Si wafer immersed in HF (4.6 M) and AgNO 3 solution, with the variation concentration of 15-35 mM, for one minute. Consequently, the Si wafers covered with Ag particles were etched in HF (4.8 M) and H 2 O 2 (0.4 M) solution for the formation of vertically aligned SiNWs. We found that the size and density of SiNWs decreased with the increase of AgNO 3 concentration. After a delay time of about 30-40 min, the SiNWs growth depended linearly on the etching time. The light emission from the prepared SiNWs observed at room temperature was well resolved with two bands at around 450 nm (~2.75 eV) and 700 nm (~1.77 eV). The origins of the two emission bands and the comparative aspects are presented and discussed.
Nanoscale Research Letters, 2012
We study the structure and optical properties of arrays of silicon nanowires (SiNWs) with a mean diameter of approximately 100 nm and length of about 1-25 μm formed on crystalline silicon (c-Si) substrates by using metal-assisted chemical etching in hydrofluoric acid solutions. In the middle infrared spectral region, the reflectance and transmittance of the formed SiNW arrays can be described in the framework of an effective medium with the effective refractive index of about 1.3 (porosity, approximately 75%), while a strong light scattering for wavelength of 0.3 Ä 1 μm results in a decrease of the total reflectance of 1%-5%, which cannot be described in the effective medium approximation. The Raman scattering intensity under excitation at approximately 1 μm increases strongly in the sample with SiNWs in comparison with that in c-Si substrate. This effect is related to an increase of the light-matter interaction time due to the strong scattering of the excitation light in SiNW array. The prepared SiNWs are discussed as a kind of 'black silicon', which can be formed in a large scale and can be used for photonic applications as well as in molecular sensing.