Abstract:The problem of determining the porous silicon (PSi) optical constants, thickness, porosity, and surface quality using just reflectance data is board employing evolutionary algorithms. The reflectance measurements were carried out of PSi films over crystalline silicon (c-Si) substrate, and the fitting procedure was done by using a genetic algorithm. The PSi is treated as a mixture of c-Si and air. Therefore, its effective optical constants can be correlated with the porosity trough effective medium approximatio… Show more
“…For this reason, we decided to use the Looyenga effective medium approximation (LEMA) to describe the effective dielectric function in the theoretical model of the optical response. The LEMA formula does not consider a regular geometry of the incrustations and is defined by equation [21]…”
The presented experiments and studies are intended for photovoltaic applications of crystalline silicon. This work deals with chemical treatment of the surface of n-type silicon wafers with different resistivity to reduce their reflectivity. Chemical surface treatment of silicon is an alternative method to using the antireflection layer. Optical losses caused by the reflection of light from the surface of the solar cells significantly reduce their efficiency. The investigated samples were prepared by the electrochemical etching method in the solution based on hydrofluoric acid and ethanol. The analysis of the prepared samples is divided into two parts, namely experimental measurements, and theoretical modeling. Experimental measurements are performed using UV-VIS spectroscopy, spectroscopic ellipsometry and SEM microscopy. Theoretical modeling is based on the construction and optimization of theoretical model of optical response (reflectivity and ellipsometric parameters) to determine the effective refractive index and thickness of formed structure. Effective refractive index of studied samples in theoretical model of optical response is based on Looyenga effective medium approximation and Tauc-Lorentz dispersion model.
“…For this reason, we decided to use the Looyenga effective medium approximation (LEMA) to describe the effective dielectric function in the theoretical model of the optical response. The LEMA formula does not consider a regular geometry of the incrustations and is defined by equation [21]…”
The presented experiments and studies are intended for photovoltaic applications of crystalline silicon. This work deals with chemical treatment of the surface of n-type silicon wafers with different resistivity to reduce their reflectivity. Chemical surface treatment of silicon is an alternative method to using the antireflection layer. Optical losses caused by the reflection of light from the surface of the solar cells significantly reduce their efficiency. The investigated samples were prepared by the electrochemical etching method in the solution based on hydrofluoric acid and ethanol. The analysis of the prepared samples is divided into two parts, namely experimental measurements, and theoretical modeling. Experimental measurements are performed using UV-VIS spectroscopy, spectroscopic ellipsometry and SEM microscopy. Theoretical modeling is based on the construction and optimization of theoretical model of optical response (reflectivity and ellipsometric parameters) to determine the effective refractive index and thickness of formed structure. Effective refractive index of studied samples in theoretical model of optical response is based on Looyenga effective medium approximation and Tauc-Lorentz dispersion model.
“…1 shows, the increase of current density rises the etching rate and film porosity producing a reduction of the PA cycle. After that, reflectance spectra were measured and fitted by using genetic algorithms (GA) reported by Ramirez-Gutierrez 51–53 to determine simultaneously the effective porosity (Fig. 3b), interface roughness 54 , and thickness using the Transfer Matrix Method (TMM).Figure 3Calibration series parameters.…”
We present a methodology to fabricate one-dimensional porous silicon (PSi) photonic crystals in the visible range by controlled etching and monitored by photoacoustics. Photoacoustic can record in-situ information about changes in the optical path and chemical reaction as well as in temperature, refractive index, and roughness during porous layers formation. Radiometry imaging can determine the carrier distribution of c-Si substrate that is a fundamental parameter to obtain high-quality PSi films. An electrochemical cell was calibrated through a series of single PSi layers that allows knowing the PA amplitude period, porosity, and roughness as a function of the current density. Optical properties of single layers were determined using the reflectance response in the UV-Vis range to solve the inverse problem through genetic algorithms. PhC structures were designed using the transfer matrix method and effective media approximation.Based on the growth kinetics of PSi single layers, those structures were fabricated by electrochemical etching monitored and controlled by in-situ photoacoustics.
“…In the porous silicon a gradual change of the refractive index is observed. Another important factor influencing the calculation of layer thickness is roughness at the interfaces air/b-Si and b-Si/Si [16]. For these reasons, the thickness calculation of b-Si layers and optical constants (refractive index, extinction coefficient) determination requires a different approach.…”
Section: Determination Of Thickness Of B-si Layer From the Spectral Rmentioning
confidence: 99%
“…In construction of the spectral reflectance model an effective medium approximations (EMA) are usually used. Frequently used EMA theories involve Maxwell-Garnett, Bruggeman, Lorentz-Lorentz, Drude and Looyenga theories [16,[23][24][25][26][27]. Spectral reflectances of b-Si layers were modelled in the SCOUT software by using Looyenga EMA approach suitable for porous structures, [16].…”
Section: Determination Of Thickness Of B-si Layer From the Spectral Rmentioning
In this work black silicon (b-Si) samples were prepared by anodic (electrochemical) etching of p-type silicon substrate in solution of hydrofluoric acid (HF). We studied influence of anodic etching conditions (etching time, electrical potential and current) on the spectral reflectance and Raman scattering spectra. Optical properties of b-Si structures were experimentally studied by UV-VIS (AvaSpec-2048) and Raman (Thermo DXR Raman) spectrometers. B-Si layer thickness of formed substrate were determined by using SCOUT software. Effective medium approximation theory (Looyenga) was used in construction of the reflectance model. Influence of the deformation of crystal lattice introduced during the substrate etching was studied by Raman scattering method. Teoretical model of the 1st order Raman scattering profile was constructed by using pseudo-Voigt function and the profile parameters were extracted. The values of biaxial tensile stress were estimated by using optimized Raman profile parameters.
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