Surface Morphology Of Porous Silicon Research Articles

Exploring the Influence of Solvents on Electrochemically Etched Porous Silicon Based on Photoluminescence and Surface Morphology Analysis.

Porous silicon (PSi) has promising applications in optoelectronic devices due to its efficient photoluminescence (PL). This study systematically investigates the effects of various organic solvents and their concentrations during electrochemical etching on the resulting PL and surface morphology of PSi. Ethanol, n-butanol, ethylene glycol (EG) and N,N-dimethylformamide (DMF) were employed as solvents in hydrofluoric acid (HF)-based silicon etching. The PL peak position exhibited progressive blue-shifting with increasing ethanol and EG concentrations, accompanied by reductions in the secondary peak intensity and emission linewidth. Comparatively, changes in n-butanol concentration only slightly impacted the main PL peak position. Additionally, distinct morphological transitions were observed for different solvents, with ethanol and n-butanol facilitating uniform single-layer porous structures at higher concentrations in contrast to the excessive etching caused by EG and DMF resulting in PL quenching. These results highlight the complex interdependencies between solvent parameters such as polarity, volatility and viscosity in modulating PSi properties through their influence on surface wetting, diffusion and etching kinetics. The findings provide meaningful guidelines for selecting suitable solvent conditions to tune PSi characteristics for optimized device performance.

Preparation and characterization of NiO/PSi as self-cleaning surface

Water-resistant surfaces are very important to many modern technology applications. So the progresses of hydrophobic & hydrophilic surfaces for self-cleaning applications has received widespread attention over the past years. In this paper, investigating in self-cleaning surfaces technique are presented. Nickel oxide Nanoparticles (NiONPs) were manufactured at different concentrations on the porous silicon (PSi) surface by immersion plating process, which filled with square-pores like structure which affected in classification of hydrophilic and hydrophobic surfaces. This green method to prepare Nickel oxide Nanoparticles/porous silicon (NiONPs/PSi) structures was interesting because it is effective for self-cleaning applications and is low cost and environmentally friendly. NiONPs/PSi structures characterized by the use of X-Ray Diffraction, electron microscopy scanning, Fourier-transform infrared (FTIR) analysis, Ultraviolet–visible (UV) spectroscopy, and contact angle analysis. The results show that hydrophilicity & hydrophobicity of these structures strongly depend on the surface morphology of porous silicon and the resulting the shape and distribution of NiO nanoparticles. From all results, it was found that the optimum contact angle is 118° at a NiO concentration of 10-2 M for the NiONPs/PSi structure which has hydrophobic properties as it can be used as a self-cleaning surface.

Cavity resonance tunability of porous silicon microcavities by Ar+ ion irradiation

Present work reports the effect of low-energy Ar+ ion beam irradiation on the optical properties and surface morphology of porous silicon (PSi) based optical microcavities. These microcavities were realized by an active λ/2 spacer layer sandwiched between two Distributed Bragg Reflectors fabricated by galvanostatic electrochemical etching. Low-energy 10 keV Ar+ ions at various fluences were used for this irradiation study for these microcavities and characterized. The peak in the reflectance spectra of resonant cavity shows a red-shift after ion irradiation. These experimental observations are in good agreement with transfer matrix simulations. The Raman studies show that the crystalline Si is modified in nanostructured PSi and subsequently, the structural features of Si-Si and Si-O bonds. The simulated depth profiles suggest that the penetration of Ar+ ion is limited to top two PSi layers and the reduction of effective refractive index of these two layers. These experimental findings, analytical simulations, and cavity modelling provide the evidence of resonent cavity peak tunability, optical field intensity modulation, and photon confinement within the microcavity. This approach could be useful to tune the optical properties of PSi and an effective method for producing widely tunable optical structures in Si-based photonic architectures.

Fabrication of Zinc Oxide and Nanostructured Porous Silicon Composite Micropatterns on Silicon

The luminescent properties of zinc oxide (ZnO) and nanostructured porous silicon (PSi) make these materials very appealing for photoemission applications. The current study reports on the fabrication of a composite of ZnO and nanostructured porous silicon micropatterns (ZnO + PSi micropatterns) onto heavily-doped silicon surfaces. The proposed composite micropattern is devoted to the future development of light-emitting diodes. The fabrication of the ZnO + PSi micropatterns was carried out in a two–step process. (1) A regular hexagonal micropattern of a photoresist/ZnO stack was fabricated by UV lithography on crystalline silicon substrates. (2) Before being lifted off the photoresist, nanostructured PSi micropatterns were fabricated by electrochemically etching the exposed areas of the silicon substrate. Subsequently, wet etching of the photoresist was carried out for the final development of the composite ZnO and PSi micropatterns. Further, thin films of ZnO and nanostructured PSi layers were characterized. In particular, their photoluminescent properties were analyzed, as well as their morphology and composition. The experimental PL results show that the ZnO layers have emission broadbands centered at (2.63 eV, blue), while the PSi layers show a band centered at (1.71 eV, red). Further, the emission peaks from the PSi layers can be tuned by changing their fabrication conditions. It was observed that the properties of the ZnO thin films are not influenced by either the surface morphology of PSi or by its PL emissions. Therefore, the PL properties of the composite ZnO + PSi micropatterns are equivalent to those featuring the addition of PSi layers and ZnO thin films. Accordingly, broadband optical emissions are expected to arise from a combination between the ZnO layer (blue band) and PSi (red band). Furthermore, the electrical losses associated with the PSi areas can be greatly reduced since ZnO is in contact with the Si surface. As a result, the proposed composite micropatterns might be attractive for many solid-state lighting applications, such as light-emitting diodes.

The Fabrication of PSi/ZnO Nanostructures as Chemical Sensors for the Detection of Ethanol in Solution Using an Electrochemical Impedance Technique

In this work, porous silicon (PSi) was prepared by electrochemical etching and used as a template for ZnO nanostructures. ZnO nanostructures were grown using the catalytic immersion method at different molar ratio concentrations of the precursor and stabilizer. The ZnO nanostructures were analyzed using FESEM and photoluminescence (PL) spectrometry, before tested with ethanol solution. The population of the ZnO nanostructures on PSi increased with the concentration and followed the surface morphology of PSi. The photoluminescence spectra of ZnO show two dominant peaks in the UV and visible regions. When the concentration of the precursor increased, the PL peaks in the visible region (630 nm) shifted towards the blue region of the spectrum. The PSi/ZnO nanostructure chemical sensor has a large surface area, reversing sensor and fast response in ethanol. The performance of the sensor was affected by the morphology and defect structures of the ZnO nanostructures layer.

Correlation between optical properties surface morphology of porous silicon electrodeposited by Fe3+ ion

In this paper, we analyze the photoluminescence spectra (PL) of porous silicon (PS) layer which is elaborated by electrochemical etching and passivated by Fe3+ ions (PSF) via current density, electro-deposition and temperature measurements. We observe unusual surface morphology of PSF surface and anomalous emission behavior. The PSF surface shows regular distribution of cracks, leaving isolated regions or “platelets” of nearly uniform thickness. These cracks become more pronounced for high current densities. The temperature dependence of the PL peak energy (EPL) presents anomalous behaviors, i.e., the PL peak energy shows a successive red/blue/redshift (S-shaped behavior) with increasing temperature that we attribute to the existence of strong potential fluctuations induced by the electrochemical etching of PS layers. A competition process between localized and delocalized excitons is used to discuss these PL properties. In this case, the potential confinement plays a key role on the enhancement of PL intensity in PSF. To explain the temperature dependence of the PL intensity, we have proposed a recombination model based on the tunneling and dissociation of excitons.

Effect of Electrochemical Reaction Enviroment on the Surface Morphology and Photoluminescence of Porous Silicon

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 wet-etching 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.

Photo-induced electrochemical anodization of p-type silicon: achievement and demonstration of long term surface stability

Surface stability is achieved and demonstrated by porous silicon (PS) fabricated using a wavelength-dependent photo-electrochemical (PEC) anodization technique. During anodization, the photon flux for all wavelengths was kept constant while only the effect of light wavelength on the surface morphology of PS was investigated. PS optical sensors were realized, characterized and tested using a photoluminescence (PL) quenching technique. An aliphatic chain of alcohols (methanol to n-octanol) was detected in the range of 10–200 ppm. Long term surface stability was observed from samples prepared under red (750–620 nm) and green illumination (570–495 nm), where the PL quenching cycles evoke the possibility of using PS for stable sensor device applications. This study provides a route for preparing highly sensitive organic vapour sensors with a precise selection of the fabrication parameters and demonstrating their prolonged performance.

Electrochemically Deposited Aluminum in Template of Porous Silicon Film

In this article, we report on the observations that in the aqueous electrolyte of aluminum nitrate, the thin metallic conducting films on both internal and external surface of porous silicon (PS) thin films that emit visible photoluminescence at room temperature prior to electrochemical deposition have been obtained under electrochemical deposition condition. Add to this high surface-to-volume ratio and these make it a good candidate for the catalyst supporter. We have investigated the surface morphology of PS after the interval of about 30 hours of electrochemically deposited aluminum by means of scanning electron microscopy (SEM). It has been shown from SEM images that not only micrometer-sized pores are smoothed by deposition of aluminum microcrystal, but also the presences of semi-sphere aluminum microcrystal which rooted in the tip of micrometer-sized pores are observed. On the one hand, this extremely interesting phenomenon which the micrometer-sized pores are smoothed may be explained in terms of principle of electrochemical deposition; on the other hand, we have laid the formation mechanism of semi-spherical aluminum microcrystal at the door of Gibbs free energy.

The effect of Al and B on the luminescent property of porous silicon

In this paper, we studied the PL property and the surface morphology of porous silicon prepared from N-type single silicon wafers coated with and without Al film. By introducing the Al film on the surface of silicon wafer before etching, the morphology of porous silicon exhibits obvious discrimination compared with that of the conventional porous silicon, which can be explained by the formation mechanism of the samples, and the emission property of two-type porous silicon also showed the clear difference, which may be attributed to the discrepancy in the structural configuration of the samples. Furthermore, it was found that the blue emission decreased and the green emission was almost completely quenched after boron-particle deposition, which is attributed to the structural change or annihilation of the emission defects during annealing process.

STRUCTURAL AND PHOTOLUMINESCENCE PROPERTIES OF POROUS SILICON: EFFECT OF HF CONCENTRATION

Structural and Photoluminescence (PL) studies are carried out for p-type porous silicon materials prepared with different Hydrogen Fluoride (HF) concentration. Surface morphology of porous silicon was analyzed using atomic force microscope (AFM). Fourier Transform Infra Red (FTIR) spectra indicate that surface of porous silicon contain chemical species like SiH n. PL studies reveal that there is a prominent emission peak around 625 nm. No spectral shift is observed. It is further observed that the emission intensity increases with HF concentration. The PL of the porous silicon layer was found to come from its upper part, which was confirmed by a simulation of the PL spectrum employing an optical model. The refractive indices of the porous silicon layer were also determined through this simulation. The large hydrogen concentration in freshly prepared material has led to the suggestion that a silicon–hydrogen alloy effect is responsible for the luminescence.

Comparative investigation of photoluminescence of silicon wire structures and silicon oxide films

Photoluminescence spectra and their dependence on temperature as well as Raman scattering spectra and Atomic Force Microscopy investigations have been used to study the peculiarities of the red photoluminescence band in low-dimensional Si structures, such as porous silicon and silicon oxide films. It has been shown that the red photoluminescence band of porous silicon is complex and can be decomposed into two elementary bands. It was discovered that elementary band intensities depend very much on surface morphology of porous silicon. The same positions of the photoluminescence bands are also observed in silicon oxide films for different oxide composition. Comparative investigation of the PL temperature dependences in porous silicon and silicon oxide films indicates that silicon-oxide defect related mechanisms of some elementary photoluminescence bands are involved.

Modification of surface morphology and optoelectronic response in porous Si films by electrochemical methods

The effect of varied H+concentration on surface morphology of porous silicon (PS) is observed by atomic force microscopy technique. A new mechanism of PS formation concerning H+ effect is proposed. The photoluminescence (PL) spectra of two typical PS samples have different responses in the short-wavelength region. Surface photovoltage spectra results imply that the short-wavelength PL band of the PS sample prepared in high H+ concentration may be related to direct band-gap transition.

Spectral and structural features of porous silicon prepared by chemical and electrochemical etching processes

The surface morphology of porous silicon, produced by both chemical and electrochemical means, is studied by scanning force microscopy. Observed surface features in the macroscopic range (larger than 30 μm) include etch pits as well as rings and plateaus which are associated with hydrostatic forces during the etching process. In the microscopic regime (several hundred nanometers to a few microns) small hillocks, around 1 μm in diameter and approximately 100 nm high, dominate the surface structure. Missing hillocks are associated with nascent etch pits and etch pit growth is suggested to occur in steps by the rapid corrosive attack on a destabilized hillock. The presence and shape of the hillocks are attributed to surface strain which collapses the etched material. The strain can become so large as to lift the porous silicon from the surface, damaging the sample. The fluorescent properties of these materials is also discussed.