Surface Of Porous Silicon Layer Research Articles

Porous silicon biosensors based on reflectometric ‎interference Fourier transform spectroscopy- theoretical ‎foundations and experimental results

Porous silicon (PSi) biosensor based on reflectometric interference Fourier transform spectroscopy ‎‎(RIFTS) has received a lot of attention due to its applicability as a label-free biosensor. In this ‎approach, light is illuminated on the surface of a PSi layer and the interference pattern of all reflected ‎beams from all interfaces is recorded. After exposing the PSi surface to bioanalyte, depending on ‎analyte's size, it absorbs on the surface of PSi layer or penetrates to the pores and absorbs on the wall of ‎the pores. This phenomenon causes variation in the refractive index of the interface of PSi/environment ‎or in the refractive index of the layer respectively. As a consequence, decrease in peak intensity or shift ‎in the peak position of fast Fourier transform of the interference pattern is observable, which can then ‎be used as a key parameter for biosensing applications. In this work, theoretical foundations of RIFTS ‎method were discussed. Then the experimental details of using this method for biosensing applications ‎on modified porous silicon were described. Finally, experimental data for diagnosis of Osteocalcin ‎protein, a piece of VKORC1 gen and Escherichia coli bacteria by RIFTS methods were illustrated.‎

Photosensitive Heterostructures on the Basis of Nanocrystal Porous Silicon

In this work the investigations of technology, morphology, electric and photoelectric properties of the silicon photosensitive structures have been represented. The structures included layers of the silicon carbide and the porous silicon. The porous layer was formed on the surface of the single crystal silicon substrates by the method of electrolytic etching in fluoride containing solutions. Plates with different microrelief surface (polished, honed, textured) were used. Carbidization of the samples leading to the formation of heterostructures on SiC/Si was conducted by the method of gas endotaxin in a hydrogen stream in a vertical reactor with cold walls and a graphite container. The structure and composition of the SiC/Si heterostructures on the different surface structures of poly − and single crystal silicon, including surface of porous silicon layer have been investigated. We show that in the process of endotaxy of all types of surfaces forms a single crystal silicon carbide phase of cubic modification. The morphology of the resultant structures has been investigated by scanning and transmission electron microscopes. Different filiform formations were found on the pore − free surface, which are identified as silicon carbide, and the cylindrical or conical structures of the unclear nature were observed on the porous surface. The current − voltage and current − power curves have been plotted for all types of the structures, the general appearance of which indicates the presence of several potential barriers. The photoelectric properties of the structures have been analyzed along with the prospect of their use in solar cells.

Atomic and electronic structure of the surface of porous silicon layers

Atomic and electronic structure of the surface layers of porous silicon was studied by the methods of the near fine structure spectroscopy at the edge of X-ray absorption and ultrasoft X-ray emission spectroscopy. The thickness of the oxide layer and the degree of distortion of silicon-oxygen tetrahedra in this layer were estimated. The thickness of the surface oxide layer on the amorphous layer covering the nanocrystals of porous silicon that was kept during one year is several times greater than the thickness of the natural oxide in the single crystal silicon wafers. Distortion of the silicon-oxygen tetrahedron, the basic structural units of the silicon oxide, is accompanied by elongation of Si-O bonds and an increase in the Si-O-Si bond angles.

Effect of halogens on the formation and properties of the porous silicon layers

The method of atomic-force microscopy is used to study the morphology of the surface of porous silicon layers formed on the p-Si substrate and obtained by anodic etching in an electrolyte with addition of free halogens (bromine, iodine) and potassium halogenides (KCl, KI). It is established that the presence of halogens in the electrolyte is conducive to formation of large pores with the diameter as large as 150 nm. The mechanism of an increase in the pore sizes with involvement of halogens is related to an increase in the concentration of free holes due to formation of donor-acceptor pairs in the case of adsorption of halogens on the silicon surface.

Formation Mechanism of Porous Silicon Layer by Anodization in HF Solution

The mechanism of formation of porous silicon layer (PSL) has been studied according to the following experimental results. PSL is formed by the local dissolution of silicon which occurs only at the base of the pores. The concentration of the electrolyte in the pores of PSL is constant during anodization and the anodic reaction in the pores proceeds uniformly in the thickness direction. The dissolution of silicon in the pores is the results of the divalent and the tetravalent reactions of silicon with , without the disproportionation reaction. The insoluble surface porous film (SPF) exists at the surface of PSL and the silicic acid is formed in PSL. A model of forming PSL is proposed, with emphasis being placed on the anodic reaction and the local dissolution of silicon which is initiated by SPF and is promoted by the hindrance layers composed of the silicic acid.

Oxidation of Porous Silicon and Properties of Its Oxide Film

The mechanism of oxidation of a porous silicon layer (PSL) was studied by examining the oxidation progress, the temperature dependence of the oxidation and the infrared absorption spectra. It is found that the oxidation of PSL is controlled by a surface reaction at both the surface of PSL and the wall of pores in PSL. The progress of the oxidation in PSL is altered at nearly 900°C. Si2O3 as well as SiO2 are produced by low temperature oxidation below 400°C and physically-absorbed water exists in an oxidized porous silicon (OPS) film formed by wet O2 oxidation at temperatures below 700°C. Further, the properties of the OPS film are reported. Etching rate, dielectric constant, tan δ and breakdown strength of the OPS film are strongly dependent on the oxidation temperature, oxidation atmosphere and substrate resistivity. Thick OPS film, which has the same properties as thermal SiO2 of bulk silicon, is formed in a short time by high temperature oxidation above 1000°C in wet O2.