Characterization Of Porous Silicon Research Articles

Production and characterization of porous silicon via laser-assisted etching as photodetector: effect of different HF concentrations

Production and characterization of porous silicon via laser-assisted etching as photodetector: effect of different HF concentrations

Production and characterization of porous silicon via laser-assisted etching: Effect of gamma irradiation

In this research, we investigate that Gamma-rays may be used to affect the morphology of pores and the size of porous silicon. Porous silicon (PS) has been produced from the n-type silicon wafers of (111) orientations with the use of the approach of the laser-assisted etching, the samples have been anodized in a solution of HF:C2H2OH concentration 18%. X-ray diffraction (XRD), Atomic force microscopy (AFM), Photoluminescence (PL) and Raman spectroscopy were utilized for the characterization of morphological, optical and structural characteristics of the PS. Before irradiation, the AFM images reveal a dense and randomly dispersed network of pores that cover the whole surface and it is of varying size and pyramidal form. The pores seem more obvious, distinguish, that has larger diameters after 16 Gy Gamma irradiation. Before and after irradiation, the XRD pattern shows significant <111> peaks at 28.3° and 28.6°, respectively, indicating that the structure is cubic. After irradiation with gamma rays, the PL intensity in modified PS samples slight decreased, and the wavelength peaks of the PL spectra shifted to the left. Raman spectra of PS prior to and post the irradiation revealed a highly symmetric band structure. Because of new pores forming inside the first layer of PS the roughness of the samples increases with irradiation indicating that it may be utilized in optoelectronic applications.

Synthesis and characterization of porous silicon as hydroxyapatite host matrix of biomedical applications.

In this work, porous-silicon samples were prepared by electrochemical etching on p-type (B-doped) Silicon (Si) wafers. Hydrofluoric acid (HF)-ethanol (C2H5OH) [HF:Et] and Hydrofluoric acid (HF)-dimethylformamide (DMF-C3H7NO) [HF:DMF] solution concentrations were varied between [1:2]—[1:3] and [1:7]—[1:9], respectively. Effects of synthesis parameters, like current density, solution concentrations, reaction time, on morphological properties were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements. Pore sizes varying from 20 nm to micrometers were obtained for long reaction times and [HF:Et] [1:2] concentrations; while pore sizes in the same order were observed for [HF:DMF] [1:7], but for shorter reaction time. Greater surface uniformity and pore distribution was obtained for a current density of around 8 mA/cm2 using solutions with DMF. A correlation between reflectance measurements and pore size is presented. The porous-silicon samples were used as substrate for hydroxyapatite growth by sol-gel method. X-ray diffraction (XRD) and SEM were used to characterize the layers grown. It was found that the layer topography obtained on PS samples was characterized by the evidence of Hydroxyapatite in the inter-pore regions and over the surface.

Study on the Effect of Porous Silicon Sizes for Potential Visible Photodetector

In this work, the characterization of porous silicon (PS) for potential visible light emission was investigated by simulation. SILVACO TCAD simulator was used to simulate PS by using process simulator, ATHENA and device simulator, ATLAS. Different pore diameter sizes of the PS structures were constructed. The structural, optical and electrical characteristics of the structures PS were investigated by current-voltage (I-V), current gain, spectral response and the energy band gap. It was observed that PS enhances the current gain compare to bulk Si and exhibited photo emission in the visible spectrum which constitutes to the quantum confinement effect of the Si in the PS structures.

Preparation and Characterization of Porous Silicon and Carbon Composite as an Anode Material for Lithium Rechargeable Batteries

The composite of porous silicon (Si) and amorphous carbon (C) is prepared by pyrolysis of a nano-porous Si + pitch mixture. The nano-porous Si is prepared by mechanical milling of magnesium powder with silicon monoxide (SiO) followed by removal of MgO with hydrochloric acid (etching process). The Brunauer-Emmett-Teller (BET) surface area of porous Si (<TEX>$64.52m^2g^{-1}$</TEX>) is much higher than that before etching Si/MgO (<TEX>$4.28m^2g^{-1}$</TEX>) which indicates pores are formed in Si after the etching process. Cycling stability is examined for the nano-porous Si + C composite and the result is compared with the composite of nonporous Si + C. The capacity retention of the former composite is 59.6% after 50 charge/discharge cycles while the latter shows only 28.0%. The pores of Si formed after the etching process is believed to accommodate large volumetric change of Si during charging and discharging process.

Investigation of Boron Doped Nanocrystalline Diamond Films Grown on Porous Silicon Substrate under Different Doping Concentrations

The production and characterization of porous silicon (PS) samples were studied as well as their use as substrates to grow boron doped nanocrystalline diamond (NCD) films. PS represents a suitable material for diamond growth due to its large number of nucleation sites and surface area, becoming an excellent material for porous electrodes. NCD films were grown by chemical vapor deposition (CVD) technique by balancing H2/CH4/Ar gas mixture, at two different boron levels. Doping was conducted by an additional hydrogen line passing through a bubbler containing B2O3 dissolved in methanol. Two ratios of boron/carbon were used of 2000 and 20000 ppm in the bubbler solution. Scanning electron microscopy, Raman spectroscopy and X-ray diffraction were used to characterize the films as well as the PS substrate. Results showed that it is possible to obtain NCD films on PS substrate with good quality at different doping levels.

Formation and characterization of porous silicon–samarium/gadolinium nanocomposites: effect of substrate oxidation and biosynthesis process

Samarium and gadolinium nanoparticles synthesized by bioreduction process have been incorporated into nanostructured porous silicon template to form a nanocomposite. The structural and optical properties of PS–Gd and PS–Sm nanocomposites have been studied through TEM, SEM and UV–Vis spectroscopy. Extent of infiltration has been verified through reflectance interference Fourier transform spectroscopy as a function of substrate oxidation conditions. The substrates oxidized at 600 °C showed the maximum infiltration and the corresponding change of optical thickness due to nanoparticles. Such biodegradable nanocomposites in the form of particles can have potential applications in localized drug delivery and enhancement of the image contrast and optoelectronic devices. The results here reported open an energy-cheap procedure to take advantages of small rare earth nanoparticles and produced nanocomposites with their immersion in SiO2 substrates, with the perspective to be replied in other similar substrates under controlled conditions.

AFM Characterization of PS Prepared in Different Concentration of Hydrofluoric Acid

The effect of HF concentration on the surface structure of porous silicon (PS) was carefully investigated by the AFM characterization. The results showed that no pores were present on PS surface which was prepared under the higher concentration of HF (10%). However, the pores were gradually visible with the HF concentration reduction. The main pores diameter was about 100 nm, when the concentration is 5.71%. The data of surface roughness and the main height distribution of the “hill” both showed an increase with the reduction of concentration, from 6.39 nm increase to 16.9 nm and from 30 nm increase to 90 nm, respectively, which implied that the pores were better exposed under the lower HF concentration.

Preparation and Characterization of Porous Silicon in HF-AgNO3 Solution

Porous silicon (PS) of uniform structure was prepared by electroless silver deposition on surface of silicon at near room temperature in HF-AgNO3 system solution. Morphology of PS was characterized by scanning electron microscopy. The results showed that the diameter of hole was 1-2μm and holes distributed regularly. The ethylene diamine tetra acetic acid (EDTA) was an important additive to control the etching rate of silicon, which is of great significance to research the mechanism of porous silicon formation. Furthermore, photoluminescence property of PS was characterized.

Characterization of porous silicon nitride/silicon oxynitride composite ceramics produced by sol infiltration

Porous silicon nitride/silicon oxynitride composite ceramics were fabricated by silica sol infiltration of aqueous gelcasting prefabricated Si 3N 4 green compact. Silica was introduced by infiltration to increase the green density of specimens, so suitable properties with low shrinkage of ceramics were achieved during sintering at low temperature. Si 2N 2O was formed through reaction between Si 3N 4 and silica sol at a temperature above 1550 °C. Si 3N 4/Si 2N 2O composite ceramics with a low linear shrinkage of 1.3–5.7%, a superior strength of 95–180 MPa and a moderate dielectric constant of 4.0–5.0 (at 21–39 GHz) were obtained by varying infiltration cycle and sintering temperature.

Microstructural characterization of porous silicon for use in optoelectronic devices

Spectroscopic ellipsometry in the mid infrared spectral range, Raman scattering and TEM measurements on (100) oriented p(+) and n(+)-type porous silicon (PS) samples were carried out. Porosities of 68% and 48% for p(+) and n(+) wafers, respectively, and thicknesses of 27.6 mu m and 14 mu m with the same extinction coefficient k = 0.1 were determined from spectroscopic ellipsometry. Raman scattering measurements show that the resultant surface morphology of the PS layers consists of irregular and randomly distributed nanocrystalline Si structures. Using the phonon confinement model, the diameters of Si nanocrystallites have been estimated as 8 and 3 nm for p(+) PS type and 12 and 5 nm for n(+) PS type. Transmission electron microscopy shows clearly defined pores with sizes ranging from 15 to 35 nm, inhomogeneously distributed along the PS surface. We demonstrate that the filling of the PS pores by organic material (Rhodamine 6G) brings about important enhancement on photoluminescence intensity.

Light Emission and Scanning Electron Microscopic Characterization of Porous Silicon

Optical emission resulting from sputtered species during ion bombardment of porous and oxidized porous silicon targets has been studied. Samples were bombarded with 5‐keV Kr+ ions at an incidence angle of 70 degrees, and the light emitted was analyzed over the wavelength range 200–300 nm. The surface morphology was investigated, and the micrographs revealed grooves parallel to the plane of incidence when the porosity was surprisingly observed in the grooves under each pore. The results are discussed as a function of the incidence angle and the porosity of the silicon targets.

Optical characterization of porous silicon and crystalline silicon by the Kramers-Kronig method

The electronic structure of porous silicon (PS) has been characterized by optical reflectance spectra analyses. Using a Cary-500 spectrometer, the reflectance spectra of PS are measured in the photon energy range of 0.4-6 eV. The spectral responses of optical constants are calculated for PS and Si by Kramers-Kronig analysis. The analysis clarified strong evidence for widening and direct bandgaps for PS samples. Also, the optical constants of PS layers as a function of porosity have been studied. Our results indicate that PS retains some of the characteristic optical features of crystalline Si. However, in the visible region, PS shows that the imaginary part of the complex refractive index increases, and the real part decreases as porosity increases. This feature could be related to the surface roughness of PS and its role in surface absorption and scattering.

Characterization of Porous Silicon with Various Conditions and Mathematical Approach

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Morphology Study of a Hybrid Structure Based on Porous Silicon and Polypyrrole

AbstractDouble layer structures of porous silicon (PS) and polypyrrole (PPy) were prepared in order to study their electrical properties. PS was prepared by electrochemical etching in a HF/Ethanol solution from n-type silicon wafer and PPy by galvanstatic method in a lithium perchlorate/monomer solution. The experimental parameters for preparation of PS and PPy were varied to obtain different morphology of the PS/PPy structures. The surface topography of these structures was analyzed by Atomic Force Morphology (AFM). Tip- and agglomerate-like morphologies of PPy were obtained on PS layers with different pore diameters. The electrical and AFM characterization of PS were studied with and without PPy. Current-voltage (I-V) curves of PS/PPy structures were obtained in dark and under illumination. PS without PPy shows an exponential behavior in the current ((+)Al/n-Si/PS/Cu(-)), but it is almost linear when the PPy layer is deposited over the PS layer ((+)Al/n-Si/PS-PPy/Cu(-)). All structures present photovoltage under illumination conditions. However, this parameter is smaller in Al/n-Si/PS-PPy/Cu structure than Al/n-Si/PS/Cu. The open circuit voltage (VOC) and short circuit current density (JSC) of these structures decrease when the surface morphology of PPy is tip-like, but JSC increase when the surface morphology of PPy is agglomerate-like.

Development and Characterization of Porous Silicon (a Review)

Development and Characterization of Porous Silicon (a Review)

Characterization of porous silicon by means of photoacoustic spectroscopy

We investigated the characteristics of photoluminescent porous silicon by means of photoacoustic spectroscopy. The efficiency of photoluminescence (PL) from porous silicon varied from sample to sample. From porous silicon with little efficiency in PL, a wide absorption edge was observed in photoacoustic spectra. The energy region of the edge was laid from 1.3 eV to 2.4 eV, where photoluminescence was observed. On the other hand, a photoacoustic spectroscopic signal from porous silicon with high efficiency in PL was found to be constant in this energy region. From these results, we believe that non-radiative relaxation process lowers the PL efficiency of porous silicon.

Characterization of porous silicon by Raman scattering and photoluminescence

The structural and light-emitting properties of porous Si prepared from differently doped p-type Si (111) substrates have been studied by Raman scattering and photoluminescence (PL). A detailed analysis of the Raman line shapes was performed using a quantum phonon confinement model with realistic LO and TO phonon dispersion curves. Prevailing Si nanocrystallite types (spheres or wires) and characteristic sizes were determined for samples with porosities from 30 to 80%. The highly porous samples consist of fine Si spheres, while those of lower porosity are mostly wire-like. The PL spectra are less size-sensitive than the Raman ones and no clear correlation between the structural information from the Raman scattering and the PL has been observed. © 1997 Elsevier Science S.A.

Photothermal and photoacoustic characterization of porous silicon

Recently, porous silicon has been extensively studied due to its luminescence properties and some interesting features for micromechanical technology, characteristics that have led to a wide range of applications, from electro-optical devices to IR radiation detectors and gas sensors. It is therefore very important to obtain a complete description of this material, measuring its optical, electronic, and thermal properties. Following an introduction of the production process of porous silicon and its main physical and morphological characteristics, a review is presented of the possible applications of photothermal and photoacoustic techniques for the measurement of optical absorption and electronic and thermal transport properties.

Characterization of Porous Silicon by Solid-State Nuclear Magnetic Resonance

Solid-state nuclear magnetic resonance (NMR) was used to characterize porous silicon (PS) surfaces. On freshly prepared samples, the range of hydrogen content measured by 1H NMR was equivalent to 0.5−3 monolayers, while fluorine concentrations were below the 19F NMR detection limit. The 1H nuclei were used to selectively cross-polarize (CP) 29Si near the hydrogen passivation. This method was used to study the passivation of an as-prepared, thick (116 μm), high surface area (893 m2/g), photoluminescent (700 nm) PS sample. CP followed by polarization inversion (CPPI) provided some spectral editing. Changes resulting from low-temperature annealing in air and an HF soak were followed by both NMR and infrared spectroscopy. The features of the 29Si NMR spectra are assigned as (O)2(Si)Si−H (−50 ppm), (O)3Si−H (−84 ppm), (Si)3Si−H (−91 ppm), (Si)2Si−H2 (−102 ppm), and (O)4Si (−109 ppm). These assignments are discussed in relationship to experimental measurements and correlations of 29Si NMR chemical shifts for other materials. The 29Si NMR line widths for PS fall between those for crystalline silicon and those for amorphous hydrogenated silicon (a-Si:H), suggesting that disorder near the PS surface is intermediate between these extremes. However, comparision of the isotropic chemical shift values shows that the bonding in the disordered regions of PS differs from that found in a-Si:H. In addition, the sharp 29Si NMR resonance observed in the bulk single crystal starting material cannot be resolved in the spectra of PS. Thus, well-ordered silicon nanocrystallites in the PS are several bond lengths removed from hydrogen or comprise only a small fraction of the PS layer.