In this work, we demonstrate the beneficial effect of introducing a superficial porous silicon layer on the electronic quality of multi-crystalline silicon for photovoltaic cell application. The porous silicon was formed using an acid vapor etching-based method. The porous silicon layer rich in hydrogen and oxygen formed by vapor etching is an excellent passivating agent for the mc-Si surface. Laser beam-induced current (LBIC) analysis of the exponentiation parameter (n) and surface current mapping demonstrates that oxygen and hydrogen-rich porous silicon led to excellent surface passivation with a strong electronic quality improvement of multi-crystalline silicon.  It was found that the generated current of treated silicon by acid vapor etching-based method is 20 times greater as compared to the reference substrate, owing to recombination centers passivation of the grains and grain boundaries (GBs); The actual study revealed an apparent decrease in the recombination velocity of the minority carrier as reflected by 25% decrease in the exponentiation parameter (n) of the LBIC versus X-position measurements. These results make achieved porous silicon a good option for advancing efficient photovoltaic cells.

We have studied the effect of increasing porosity and its microstructure surface variation on the optical and dielectric properties of porous silicon. It seems that porosity, as the surface roughness within the range of a few microns, shows quantum effect in the absorption and reflection process of porous silicon. Optical constants of porous silicon at normal incidence of light with wavelength in the range of 250-3000 nm have been calculated by Kramers-Kroning method. Our experimental analysis shows that electronic structure and dielectric properties of porous silicon are totally different from silicon. Also, it shows that porous silicon has optical response in the visible region. This difference was also verified by effective media approximation (EMA).

Nanoporous silicon powder was produced via efficient magnesiothermic reduction. In this work, the thermal effect and reduction process time were investigated on the porous silicon structure. The nanoporous silicon powders were characterized by X-ray diffraction analysis and field emission scanning electron microscopy. The results demonstrate that porous structure was changed to homogeneous and uniform porous structure when the heating ramp rate was controlled at 5 0C/min. The average pore size of uniform porous silicon was reported 195.8 nm.

In this paper, a powerful explosive system has been introduced where in porous silicon, as host matrix, is acceptor of different oxidizers. To produce porous silicon and prepare the surface, an electro-chemical etching was presented and then to prepare the related composites,the obtained product was processed. In this process, silicon single-crystal wafer as anode is electrochemically oxidized to form the porous silicon. The oxidation process depends on the parameters such as resistance, the electrolyte composition, crystallography orientation, temperature and current density. In during of the reaction, the system in proximity of HF is converted to and: Si + 2H+ + 6HF SiF62- + 2H2 + 4H+In the next stage, the produced pores by particular ways are filled with oxidizer agents that will change obtained product explosion properties depending on the filler type. In these cases, nitrate and perchlorate salts are usually used as oxidizer constituents. The obtained products have favorite mechanical stability, combust in normal and controllable ways and have long- time life.The performance energy and the obtained reaction rate are predictable and repeatable.The maximum energy release is 28 KJ/gr for this explosion and combustion temperature range was between 2900 K and 4100 K.

Porous silicon (PS) samples are obtained by electrochemical anodization of Si wafers in HFು solution. The hydrogen complex components are formed on the inner surface walls of porous silicon. In this work the depth profile of porous silicon is estimated by measurement of hydrogen content in the depth of the sample. Since the well-known ion beam analysis simulation programs are inappropriate for simulating porous materials, a Monte-Carlo simulation program is developed to obtain the most consistent depth profiles with the experimental ones. Hydrogen content in the depth of the sample is considered to be proportional to the porosity of the sample. The results indicate that the maximum porosity of the sample is 90% for 69-139 nm depth of the sample.

The development of an efficient adsorbent for phosphate removal from wastewater to prevent the eutrophication of surface waters is very important. In this study, porous silicon powder prepared with acidic etching solution (HF: HNO3: H2O). Then, Zirconium-modified porous silicon has been synthesized by a simple and low-cost hydrothermal process. The morphology and structure of the samples were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD). This material has been used as an adsorbent for phosphate ion (PO43-) removal from synthetic aqueous solutions. The effect of operating conditions such as contact time, initial anion concentration, pH, the presence of competitive ions on the adsorption performances and the regeneration of the adsorbent have been investigated. Maximum adsorption amount of 47.7 mg P/g has been obtained at ambient temperature. The maximum removal of phosphate was reached at pH= 4 for Zirconium-modified porous silicon. The adsorption was almost unaffected by the presence of competitive ions. Regeneration tests have shown that the adsorbent retains its capacity after 3 adsorption-desorption cycles.

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).

In this study, the effect of phosphorous concentration has been investigated on performance of porous silicon solar cells. For this purpose, silicon substrates were etched into aqueous etching solution containing hydrofluoric acid / hydrogen peroxide with molar ratios 0.82, 0.87 and 0.89 via metal-assisted chemical etching. Surface characteristics were studied by optical microscopy, field-emission electron microscopy and antireflection analysis. In the following, solar cells were fabricated by phosphorous diffusion into optimized porous silicon substrate which phosphorous concentrations had values of 3%, 9%, and 15%. The result presented that in 0.82 molar ratio, the etched silicon had uniform porosities whose sizes were nearly to Ag nano-particles. The reflectance of this substrate was decreased to 11% and was the best substrate for absorbing incident light. Survey of fabricated solar cell performance showed 98% increasing of short circuit current in the solar cell which was made by P2O5 3%. This concentration due to is near the solubility of phosphorous in silicon, caused the increasing efficiency to 10.6%.

Porous silicon (PS) layers come into existance as a result of electrochemical anodization on silicon. Although a great deal of research has been done on the formation and optical properties of this material, the exact mechanism involved is not well-understood yet. In this article, first, the optical properties of silicon and porous silicon are described. Then, previous research and the proposed models about reflection from PS and the origin of its photoluminescence are reveiwed. The reflecting and scattering, absorption and transmission of light from this material, are then investigated. These experiments include,different methods of PS sample preparation their photoluminescence, reflecting and scattering of light determining different characteristics with respect to Si bulk.

Nano-porous silicon were simply prepared from p-type single crystalline silicon wafer by electrochemical etching technique via exerting constant current density in two different HF-Ethanol and HF-Ethanol-H2O solutions. The mesoporous silicon layers were characterized by field emission scanning electron microscopy and scanning electron microscopy. The results demonstrate that the width of nano-pores changes from 7 nm to 60 nm by varying current density from 10 mA/Cm 2 to 40 mA/Cm 2, respectively and the depth of nano-pores also alters by applying different values of etching duration. It is concluded that varying current density leads to different width of pores while varying etching duration results in various depth of pores. Such etch tuning process is applicable for fabricating different nano-sized porous silicon for many modern electronic devices.