Surface Layer Of Porous Silicon Research Articles

Thickness of the surface layer of porous silicon

Semiconductor materials with nanoscale structural elements are promising materials for modern electronics. Due to this structure, porous silicon exhibits unique physicochemical properties that single crystal silicon does not possess. The literature describes two methods for producing layers of porous silicon. This is chemical staining etching without applying an external electric field and anodic electrochemical etching of a silicon wafer in an external electric field. In this paper, we discuss the problem of the surface layer of porous silicon. A layer of thickness h = d is called a d(I) layer, and a layer at h≈10d is called a d(II) layer of atomically smooth silicon. At h≈10d, the dimensional dependence of the physical properties of the material begins to appear, and such a structure is called a nanostructure. At h = d, a phase transition occurs in the surface layer. It is accompanied by sharp changes in physical properties, for example, the direct Hall-Petch effect is reversed. The analysis of the work describing the properties of porous silicon, single-crystal silicon is carried out. It has been shown that, starting from 80% porosity, silicon, by its properties of the d(II)Si layer, extends beyond the Glater nanostructure. For most pure metals, the thickness of the surface layer d(I) does not exceed 3 nm (for d(II) ~ 30 nm).

Influence of the Surface Layer on the Electrochemical Deposition of Metals and Semiconductors into Mesoporous Silicon

The influence of the surface layer on the process of the electrochemical deposition of metals and semiconductors into porous silicon is studied. It is shown that the surface layer differs in structure and electrical characteristics from the host porous silicon bulk. It is established that a decrease in the conductivity of silicon crystallites that form the surface layer of porous silicon has a positive effect on the process of the filling of porous silicon with metals and semiconductors. This is demonstrated by the example of nickel and zinc oxide. The effect can be used for the formation of nanocomposite materials on the basis of porous silicon and nanostructures with a high aspect ratio.

Increasing the efficiency of photoelectric cells by nanostructuring their surface

A method of fabrication of nanostructured objects, which increases the efficiency of the photo-electric system used in the conversion of energy of electromagnetic radiation into electric energy is suggested. The method is based on the formation of metal nanodots on the basis of the surface layer of porous silicon, which concentrates the energy of electromagnetic radiation due to localized plasmon modes.

Composite porous silicon-crystalline silicon cantilevers for enhanced biosensing

Cantilever transducers, which are recognized as a promising platform for the next generation of chemical and biological sensors, are currently under extensive research. Here we report composite porous silicon-crystalline silicon microcantilevers made of SOI wafers, where the porous silicon surface provides an excellent interface for immobilization of the biosensing layer. We start with crystalline silicon cantilevers fabricated from SOI wafers and we establish a surface layer of porous silicon on the cantilevers by vapor phase stain etching. The processed porous silicon does not introduce significant static bending of the cantilevers indicating that it does not introduce significant residual stress. It does provide an excellent biocompatible material for immobilization of a wide variety of chemical and biological materials, resulting in enhanced sensitivity as demonstrated on the covalently immobilized antibody binding its complementary antigen.

Laser-induced modification of porous silicon

We present the results of experiments on annealing the surface layer of porous silicon by pulsed IR laser radiation. The character of laser-induced modification has been studied using IR spectroscopy and transmission electron microscopy. It is shown that the proposed method can be used to obtain a Si:SiO2 composite.

Structure and Magneto-Optical Properties of “Porous Silicon–Cobalt” Granular Nanocomposites

The structural and magneto-optical properties of “porous silicon-cobalt” nanocomposites prepared through electrochemical deposition on silicon substrates of different porosities are investigated. It is revealed that, under galvanostatic conditions, cobalt micrograins are formed only in a surface layer of porous silicon. The greater the pores in silicon, the larger the mean size of the ferromagnetic micrograins. The nanocomposites thus fabricated possess ferromagnetic properties and, at specified compositions, are characterized by anomalously large magnitudes of the equatorial or transverse magneto-optical Kerr effect (TMOKE). The magneto-optical properties of the nanocomposites are simulated in the Bruggeman effective-medium approximation. It is shown that the anomalous negative transverse magneto-optical Kerr effect is associated with the oxidized state of porous silicon in the vicinity of the ferromagnetic metal micrograins.

Application of the final state Auger parameter imperfect screening model for the Si L 23VV spectrum of porous silicon

In this paper we have applied the final state Auger parameter imperfect screening model for the Si L 23VV spectrum to study the local electronic structure close to the surface layer of porous silicon prepared by anodic etching. This application has allowed to reveal the lower local high-frequency dielectric constant, conduction band electron concentration, higher band gap for porous silicon in comparison with these values for the intrinsic single crystal silicon and to evaluate the size of the silicon particles. Comparison of calculated band gap values with known one at the same silicon particle sizes have allowed us to propose the higher effective density of states in conduction band and/or in valence band for porous silicon in comparison with these values for the single crystal silicon.

Auger electron spectroscopy study of the electronic structure of porous silicon–metal interfaces

Abstract The use of Auger electron spectroscopy (AES) for the study of local chemical bonds and electronic structure has been applied to investigations of the electronic structure close to the surface layer of porous silicon and of the electronic structure of porous silicon–titanium and silicon–gold interfaces. The results obtained show that close to the surface layer of porous silicon the electron concentration in the conduction band increases under Ar + ion sputtering. This result provides confirmation of the model of an increasing energy band gap under porous silicon formation from single crystal silicon. Titanium and gold deposition leads to an increase in the high-frequency dielectric constant and in the electron concentration in the conduction band.

Luminescence of Er-implanted porous silicon

After Er + ion implantation the bright visible emissions of porous silicon (PSi) still remain. After annealing 1.54μm characteristic emissions of Er 3+ in PSi have been measured, and its intensity is much more intense than that of Si processed by same conditions. Further experiment shows that enhancement of the Er 3+ emission relates to the surface layer of porous silicon. It is probable that the impurities introduced in surface layer by electrochemical process give rise to 1.54μm luminescence enhancement.

Field emission from pyramidal cathodes covered in porous silicon

Square-based pyramidal emitters formed by wet etching of p-type silicon wafers have been anodized to give a thin surface layer of porous silicon. At the surface of such material are very small fibrils with widths ≤3 nm. Field emission measurements from pyramidal cathodes of plain and anodized silicon show a dramatic improvement, when the porous silicon is present. In this case, average peak emission currents of 25 μA have been obtained with the highest measured being 90 μA, improved uniformity between cathodes was produced and emission began at lower voltages. It was found that plain cathodes too blunt to emit did so when covered in porous silicon. The reasons why such silicon fibrils improve emission are discussed.

A Study on Michanism of VisibLe Luminescence From Fbrous SiLicon

AbstractThe efficient visible tight emitting porous silicon was made using the standard method of anodic oxidation. The characteristic photoluminescence spectra and Raman Scattering spectra of the porous silicon were obtained. A kind of stable yellow powder (not the fragments of the porous silicon thin film the porous structure was still on the crystalline silicon substrate) was taken off from the visible light emitting porous silicon with nonchemical method. The powder can not dissolve in water, alcohol, acetone and some other common solvents, and it still emits efficient visible light after further grinding. The PL spectrum of the powder shows the same peak position, the same shape and the same FW-M as that of the porous silicon wafer. The microstructure of the porous silicon wafer and the microscopic shape of thepowder were studied using the scanningelectron microscopy (SEM) The X–ray photoelectron spectroscopy MSP) shows that the fluorescent powder in the surface layer of the porous silicon is composed of many kinds of elements, such as Si, Q a N and so on. The Si content is only 50% or less in the surface layer of porous silicon. The above–mentioned experiments were performed again on the unpolished surface of the single crystal silicon substrate. So we suggest that the visible luminescence of the porous silicon is from the fluorescent powder maybe not due to the quantum confinement effect in the nm–scate crystalline silicon pillars.