Two-Scale Kirchhoff Theory: Comparison of Experimental Observations With Theoretical Prediction

We introduce a non-perturbative two scale Kirchhoff theory, in the context of light scattering by a rough surface. This is a two scale theory which considers the roughness both in the wavelength scale (small scale) and in the scales much larger than the wavelength of the incident light (large scale). The theory can precisely explain the small peaks which appear at certain scattering angles. These peaks can not be explained by one scale theories. The theory was assessed by calculating the light scattering profiles using the Atomic Force Microscope (AFM) images, as well as surface profilometer scans of a rough surface, and comparing the results with experiments. The theory is in good agreement with the experimental results.Comment: 6 pages, 8 figure

Intraband light absorption in free-standing porous silicon

We have prepared free-standing porous silicon (FPS) samples with various porosities using electrochemical etching. The result of a study combining absorption and photoluminescence (PL) from FPS samples with porosities in the range 53–76% is presented. A blue shift of the PL peak position and an increase of the PL intensity with enhancing porosity have been observed. Furthermore, the PL peak and intensity of porous silicon (PS) samples are compared with FPS samples. Our results show that the PL peak intensity reduces 1.5–2.5 times from PS to FPS. However, no notable shift of the PL peak position from PS to FPS has been observed

Simulation of doping type and current density effects on porous silicon growth by modified limited diffusion aggregation method

The aim of this article is apply modification to limited diffusion aggregation model. The method can simulate the doping type and current density on obtained structures forms within porous silicon growth. For doping type effect, the sticking coefficient parameter and for the current density effect, mean field parameter applied to limited diffusion aggregation. Simulation results showed that the sticking coefficient parameter influences pores thickness controlling. Meanwhile, the mean field parameter could control tree or rod characteristics of pores. Results on porous silicon growth simulation showed that the applied modifications accompany with these two parameters on structure simulation formation are consistence with experimental data of the samples

Porosity-dependent fractal nature of the porous silicon surface

Porous silicon films with porosity ranging from 42% to 77% were fabricated by electrochemical anodization under different current density. We used atomic force microscopy and dynamic scaling theory for deriving the surface roughness profile and processing the topography of the porous silicon layers, respectively. We first compared the topography of bare silicon surface with porous silicon and then studied the effect of the porosity of porous silicon films on their scaling behavior by using their self-affinity nature. Our work demonstrated that silicon compared to the porous silicon films has the highest Hurst parameter, indicating that the formation of porous layer due to the anodization etching of silicon surface leads to an increase of its roughness. Fractal analysis revealed that the evolution of the nanocrystallites’ fractal dimension along with porosity. Also, we found that both interface width and Hurst parameter are affected by the increase of porosity

Correlation between porosity and roughness as obtained by porous silicon nano surface scattering spectrum

Reflection spectra of four porous silicon samples under etching times of 2, 6, 10, and 14 min with current density of 10 mA/cm2 were measured. Reflection spectra behaviors for all samples were the same, but their intensities were different and decreased by increasing the etching time. The similar behavior of reflection spectra could be attributed to the electrolyte solution concentration which was the same during fabrication and reduction of reflection spectrum due to the reduction of particle size. Also, the region for the lowest intensity at reflection spectra was related to porous silicon energy gap which shows blue shift for porous silicon energy gap. Roughness study of porous silicon samples was done by scattering spectra measurements, Rayleigh criteria, and Davis-Bennet equation. Scattering spectra of the samples were measured at 10, 15, and 20 degrees by using spectrophotometer. Reflected light intensity reduced by increasing the scattering angle except for the normal scattering which agreed with Rayleigh criteria. Also, our results showed that by increasing the etching time, porosity (sizes and numbers of pores) increases and therefore light absorption increases and scattering from surface reduces. But since scattering varies with the observation scale (wavelength), the relationship between scattering and porosity differs by varying the observation scale (wavelength

Effect of gold electrode annealing on gas sensing properties of nano-and microstructures of macroporous silicon

860-863This paper presents porous silicon (PS) with nano-and microstructures as carbon dioxide sensing layers. The p-type Si substrate is subjected to PS etching. The PS morphology has been characterized by scanning electron microscope. According to the parameters of electrochemical process, PS layers were found to have a different structure. By using dimethylformamide (DMF) in electrolyte, regular, honeycomb-like and macroporous structures were formed. PS side of the substrate is then coated with a thin layer of gold and annealed at 500°C. These devices, which operate at room temperature, are more sensitive to the applied voltages in CO2 gas. The effect of annealing of gold electrode on current-voltage and response-voltage characteristics of PS has been studied. Our results show that the conductivity and response of PS sensors improve much more when its surface is modified with annealing of gold electrode and also nanostructured PS has greater response than the others. </span