Porosity Of Porous Silicon Layer Research Articles

FORMATION OF POROUS SILICON ON A HIGHLY DOPED P-TYPE MONOCRYSTALLINE SILICON

Porous silicon layers were formed on a p-type silicon wafers by electrochemical anodisation. Dependencies of thickness and porosity of porous silicon layers as well as effective valence of silicon dissolution versus anodizing time and current density were obtained and analysed. A mathematical model for growth of layers of porous silicon was developed.

Carrier transport in porous-Si/Ni/c-Si nanostructures

In the present paper we have studied the peculiarities of carrier transport properties of nanoheterostructures containing silicon substrate covered with porous silicon layer, where pores were either filled or non-filled with ferromagnetic Ni clusters. We have carried out DC conductivity experiments as a function of temperature (ranging from 2 to 300 K) and porosity of porous silicon layer (between 30% and 70%). Presence of a surface layer with high resistance on the porous silicon top and its role in nanoheterostructure formation was revealed. It was shown that specific electrochemical kinetics of Ni deposition into porous silicon significantly influences resultant nanostructure resistance and high temperature conductance activation energy.

Determination of thickness and porosity of porous silicon layer using photoacoustic technique

The thickness of thin porous layers of silicon samples and their varying porosity have been determined using photoacoustic technique (PA). The measured values of the effective thermal diffusivity (α eff ) and effective thermal effusivity (e eff ) were exploited to determine the thickness of porous silicon (p-Si) film using the effective layer model. Also the determined α eft together with the two-layer model were used to obtain the thermal diffusivity of the p-Si layer only. Using Maxwell-Rayleigh model, the porosity percentage for the different samples were determined and compared to the results obtained by scanning electron microscope (SEM) with 10 % variations.

Role of parasitics in humidity sensing by porous silicon

Abstract Humidity sensing by porous silicon (PS) layer is commonly reported either by capacitive sensing or by conductive sensing. A critical analysis of both capacitive and conductive sensing by microporous PS layer is presented here. The influences of parasitic capacitances and resistances unavoidably associated with the active porous layer on the measured changes in capacitance and resistance of the humidity sensor with variation of humidity are analysed. The role of contact geometry, signal frequency and porosity of PS layer are also discussed. It is shown that capacitive sensing is more sensitive in low frequency range owing to the relative contributions of parasitic components.

Visual determination of thickness and porosity of porous silicon layers

Optical characteristics of porous silicon layers of different thickness and porosity are simulated and interference spectra are calculated. The results are presented as curves on a colorimetric diagram. For thicknesses up to 500 nm, analysis of colors has shown that the interference color is directly related to the product of thickness and porosity of porous silicon layer. Practical techniques, which enable one to visually define thickness (or porosity) of a porous silicon layer at known porosity (or thickness), are developed. The method has high accuracy and is easy to use, it does not need destruction of the sample and allows one to make the control in selected local areas. A similar technique is useful for in-situ analysis during the porous silicon anodization process. The method applied to dried porous structures and those filled by water allows determination of both thickness and porosity of a porous silicon layer at one time. © 1997 Elsevier Science S.A.

Porosity and Pore Size Distributions of Porous Silicon Layers

Porosities of porous silicon layers formed on different types of substrates and under different experimental conditions are compared with and related to the pore size distribution determined by gas adsorption experiments. Results show that porous layers formed on lightly P‐doped silicon exhibit a network of very narrow pores, of radii less than 2 nm. Porous films formed on heavily doped silicon present larger radii, ranging between 2 and 9 nm according to the experimental conditions. Larger porosities and larger pore sizes are obtained by increasing the forming current density or by decreasing the concentration. Heavily P‐doped porous silicon layers are homogeneous in depth and generally present a quite sharp pore size distribution. With heavily N‐doped silicon, an increase in porosity with increasing thickness is found, which corresponds to an increase in pore size, leading to a broadening of size distributions. This porosity gradient is attributed to a chemical dissolution of the layer occurring during anodization. In addition, a strong dependence of porosity with small variations in doping level is found.