Effect of electrochemical reaction environment on the surface morphology and photoluminescence of porous silicon (original) (raw)
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Materials Science Forum, 2013
Porous silicon (p-Si) is a well-known silicon based material that can emit visible light at room temperature. The radiative recombination that originated from quantum confinement effect shows photoluminescence (PL) in red, while the defect on silicon oxide at the surface of p-Si shows in blue-green region. Porous silicon can be synthesized through two methods; wet-etching and electrochemical anodization using hydrofluoric acid as the main electrolyte. The electrochemical anodization is more favorable due to faster etching rate at the surface than the conventional wetetching method. The objective of this research is to show that both of porous silicons can be synthesized using the same main electrolyte but by varying the reaction environment during anodization/etching process. Here, we shows the wet-etching method that enhanced by polarization concentration will produce porous silicon with silicon oxide defects by means blue-green emission, while direct electrochemical anodization will produce samples that emit red PL signal. The effect of introducing KOH into the electrolyte was also studied in the case of enhanced-wet-etching method. Surface morphology of porous silicon and their photoluminescence were observed by Scanning Electron Microscope and PL spectroscopy, respectively.
Surface and Interface Analysis, 2012
In this paper, we present the results of studies on the photoluminescence (PL) of porous silicon (PSi) samples obtained by etching with the assistance of silver metal in different ways. If the Si sample, after being coated with a layer of silver nanoparticles, is electrochemically etched, its PL intensity becomes hundreds of times stronger than the PL intensity when it is chemically etched in the similar conditions. The difference in the PL intensities is explained partly by the anodic oxidation of silicon which occurs during the electrochemical etching process. The most obvious evidence that silicon had been oxidized anodically in the electrochemical etching process is the disappearance of the PSi layer and the appearance of the silicon oxide layer with mosaic structure when the anodization current density is large enough. The anodic oxidation has the effect of PSi surface passivation. Because of that, the PL of obtained PSi becomes stronger and more stable with time.
Porous silicon: material properties, visible photo- and electroluminescence
Applied Surface Science, 1993
Following the recent discovery of visible photo and electroluminescence of high-porosity porous silicon layers this paper presents a review of the most relevant results and models proposed to explain the phenomena. Porous silicon fabrication techniques are presented including some recommendations to allow a meaningful comparison of results obtained hy different laboratories. Recent results of pore size. surface area measurements. crystallographic structure determination and microstructure observations are discussed. Detailed studies of optical absorption coefficients of porous layers of different porosities are pt-esentetf. A clear upshift toward the visible range is explained by a quantum confinement model. Intense visible photoluminesccnce ol porous silicon layers is discussed on the ground of both quantum confinement and surface-controlled phenomena. The caaential role played by surface passivation, for efficient luminescence. is analysed. Reported results of visible electroluminescence during anodic oxidation of porous silicon layers and visible light emission from solid-state porous silicon dcviccs are reviewed.
Peculiarities of Photoluminescence in Porous Silicon Prepared by Metal-Assisted Chemical Etching
ISRN Optics, 2012
Photoluminescent (PL) porous layers were formed on p-type silicon by a metal-assisted chemical etching method using H2O2 as an oxidizing agent. Silver particles were deposited on the (100) Si surface prior to immersion in a solution of HF and H2O2. The morphology of the porous silicon (PS) layer formed by this method was investigated by atomic force microscopy (AFM). Depending on the metal-assisted chemical etching conditions, the macro- or microporous structures could be formed. Luminescence from metal-assisted chemically etched layers was measured. It was found that the PL intensity increases with increasing etching time. This behaviour is attributed to increase of the density of the silicon nanostructure. It was found the shift of PL peak to a green region with increasing of deposition time can be attributed to the change in porous morphology. Finally, the PL spectra of samples formed by high concentrated solution of AgNO3 showed two narrow peaks of emission at 520 and 550 nm. Th...
Journal of Applied Electrochemistry, 2006
Dilute HF solutions with concentrations down to 0.03% have been used to obtain luminescent porous silicon (PSi) layers on p-type Si wafers. The experimental results show that with a constant etching time of 30 min, PSi layers with sufficient luminescence efficiencies can be formed for HF concentrations as low as 0.1%. Because of a significantly lowered critical current density, only very low etching current densities of ≤ 0.1 mA cm −2 can result in the formation of luminescent PSi samples in 0.1% HF solutions. A notable result is that these low etching current densities cannot be used to form luminescent PSi layers in concentrated (≥ 1%) HF solutions. The behavior of PL intensity as a function of etching current density has been analyzed over a wide range of HF concentration. The PL intensity is determined by the ratio of the etching current density to the critical current density, suggesting that the presence of silicon oxides plays an important role in the formation of luminescent Si nanostructures in PSi layers.
In this paper, porous silicon layers was prepared from p-type silicon with orientation (100) by electrochemical etching method , samples were anodized in a solution of 48% HF and 99% C2H2OH at 1:1 ratio and study the morphology properties of PSi samples by changing etching time (15, 17 and 20) min for fixed (11.5 mA/ cm2 ) current density, and imaged PSi sample in Atomic force microscopy(AFM), which shows the rough silicon surface, with increasing etching process (etching time) porous structure nucleates which leads to an increase in the depth and width (diameter) of surface pits. Consequently, the surface roughness also increases and we found that the porosity of PSi increasing with the increasing etching time. The XRD measurements has confirmed the crystallinity nature of porous silicon. A broad peak of blue emission has also confirmed by photoluminescence (PL) measurements and it has been attributed to SiHx groups which are confirmed by FTIR spectra. Chemical fictionalization during the electrochemical etching show on surface chemical composition of PSi. From the FTIR analyses showed that the Si dangling bonds of the as-prepared PSi layers have large amount of Hydrogen to form weak Si–H bonds.
Malaysian Journal of Fundamental and Applied Sciences
Achieving high quality porous silicon (PSi) materials with desired porosity remains challenging. Three good qualities of PSi samples are prepared by Photo electro-chemically etching a piece of n-type Si inside the solution of 20 M HF, 10 M C2H5OH and 10 M H2O2 at fixed etching time duration (30 min) and varying current density (15 mA/cm2, 30 mA/cm2 and 45 mA/cm2). As-prepared sample morphologies are characterized via scanning electron microscopy (SEM) and atomic force microscopy (AFM). The gravimetric method is used to estimate the thickness and porosity of the prepared samples. Current density (etching time) dependent morphologies, electronic bandgap and room temperature photoluminescence (PL) properties of such PSi nanostructures are evaluated. These PSi structures revealed enhanced rectifying characteristics with increasing current density.
Correlation of photoluminescence spectra and structure of porous silicon
Semiconductor Science and Technology, 1996
Porous silicon (PS) layers emitting red photoluminescence (PL) have been prepared by anodization of p-type (100) monocrystalline silicon substrate in aqueous HF solutions. PS layers oxidized in free air exhibit under UV photoirradiation an intense yellow-orange PL, whilst as-prepared samples emit red PL. Our aim is to explain the PL behaviour and its origin in both unetched and HF etched as-prepared and oxidized PS layers according to calculated PL based on quantum confinement formalism and to infrared spectroscopy (IRS). It was found that the PL behaviour is associated with a quantum size effect and concentration change in quantum dots and wires. It was observed that HF etching of oxidized PS may induce a preponderance of dots or wires in the PS structure, depending on the oxidation degree, and produce a PL blueshift or redshift respectively. By correlating PL spectra of unetched and HF-etched oxidized PS, we found that highly oxidized PS transforms into an SiO 2 matrix in which photoluminescent nanocrystalline Si quantum dots are embedded.
2010
Porous silicon (PS) is defined as a composition of a silicon skeleton permeated by a network of pores or in other word, PS is a network of silicon nanowires and nanoholes which are formed when the crystalline silicon wafers are etched electrochemically in electrolyte solution such as hydrofluoric (HF) acid . PS shows different features in comparison to the bulk silicon such as shifting of fundamental absorption edge into the short wavelength and photoluminescence visible region. The PS material possesses interesting characteristics such as larger surface to volume ratio, high-intensity of nano porous structure and low refractive index. This paper presents the synthesis and characterization of electrochemically anodized PS structures. The effect of short anodization time on the PS structures is investigated. The PS surface morphology and optical properties are characterized using scanning electron microscopy (SEM) and photoluminescence (PL) spectrometer, respectively.
Effect of Silicon Crystal Size on Photoluminescence Appearance in Porous Silicon
ISRN Nanotechnology, 2011
The photoluminescence (PL) study in porous silicon (PS) with decreasing Si crystallites size among the pores was reported. The PL appearance is attributed to electronic confinement in columnar-like (or dotlike) structures of porous silicon. Three different pore diameter PS samples were prepared by electrochemical etching in HF-based solutions. Changes in porous silicon and Si crystallite size were studied by observing an asymmetric broadening and shift of the optical silicon phonons in Raman scattering. Fourier transform infrared spectroscopy (FTIR) was used to study the role of siloxene or other molecular species, for example, SiH x in the luminescence mechanism. This mechanism was further studied by thermal annealing of PS at different temperatures. The PL of PS sample annealed at ≥300 • C for 1 hr shows that trap electronic states appear in the energy gap of the smaller nano-crystal when Si-O-Si bonds are formed. From the observation of PL, Raman, and FTIR spectroscopy, the origin of PL in terms of intrinsic and extrinsic properties of nanocrystalline silicon was discussed.