Structural, Optical, and Thermophysical Properties of Mesoporous Silicon Layers: Influence of Substrate Characteristics
03 Apr 2017-Journal of Physical Chemistry C (American Chemical Society)-Vol. 121, Iss: 14, pp 7821-7828
TL;DR: In this paper, the structural, optical and thermal properties of n-type (100), p-type(100), and (111) mesoporous silicon (MePSi) are reported.
Abstract: In this paper, the structural, optical and thermal properties of n-type (100),
p-type (100) and (111) mesoporous silicon (MePSi) are reported. The mesoporous silicon was
prepared by an electrochemical process from bulk silicon wafer. Depending on the etching
depth, analyses show that the porosity of p-type (111) increased by 32 to 40% compared to p
(100) which, in turn, increased by 22 to 48% compared to n-type (100). The structure
morphology and the abundance of Si-Ox and Si-Hy also depended heavily on the type and
crystal orientation of MePSi. The thermal properties of the MePSi layers such as thermal
conductivity (κ), volumetric heat capacity (ρCp) and thermal contact resistance (Rth) were
determined using the pulsed photothermal method. The thermal conductivity of bulk silicon
dropped sharply after etching, decreasing by more than twenty-fold in the case of n-type (100)
and by over forty-five fold for p-type (100) and (111). According to the percolation model
depending on both porosity and phonon confinement, the drop in thermal conductivity was
mainly due to the nanostructure formation after etching. Thermal investigations showed that
the volumetric heat capacity (ρCp) followed the barycentric model which depends mainly on
the porosity. The thermal contact resistances of MePSi layers were estimated to be in the
range of 1x10-8 to 1x10-7 K⋅m2⋅W-1.
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References
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TL;DR: Mise au point comportant des definitions generales et la terminologie, la methodologie utilisee, les procedes experimentaux, les interpretations des donnees d'adsorption, les determinations de l'aire superficielle, and les donnes sur la mesoporosite et la microporosite.
Abstract: Mise au point comportant des definitions generales et la terminologie, la methodologie utilisee, les procedes experimentaux, les interpretations des donnees d'adsorption, les determinations de l'aire superficielle, et les donnees sur la mesoporosite et la microporosite
20,347 citations
TL;DR: In this article, the authors present a tool for the selection and appraisal of the methods of characterization of porous solids, and also give the warnings and guidelines on which the experts generally agree.
Abstract: These recommendations aim to be a tool for the selection and appraisal of the methods of characterization of porous solids, and to also give the warnings and guidelines on which the experts generally agree. For this purpose, they successively consider the description of a porous solid (definitions, terminology), the principal methods available (stereology , radiation scattering, pycnometry, adsorption, intrusion, suction, maximum buble pressure, fluid flow, immersion or adsorption calorimetry, thermoporometry , size exclusion chromatography, Xenon NMR and ultrasonic methods) and finally the general principles which are worth being followed in the selection of the appropriate method.
3,257 citations
TL;DR: In this article, the control factors controlling the growth of native silicon oxide on silicon (Si) surfaces have been identified, and the chemical bond structures for native oxide films grown in air and in ultrapure water are also discussed.
Abstract: The control factors controlling the growth of native silicon oxide on silicon (Si) surfaces have been identified. The coexistence of oxygen and water or moisture is required for growth of native oxide both in air and in ultrapure water at room temperature. Layer‐by‐layer growth of native oxide films occurs on Si surfaces exposed to air. Growth of native oxides on n‐Si in ultrapure water is described by a parabolic law, while the native oxide film thickness on n +‐Si in ultrapure water saturates at 10 A. The native oxide growth on n‐Si in ultrapure water is continuously accompanied by a dissolution of Si into the water and degrades the atomic flatness at the oxide‐Si interface, producing a rough oxide surface. A dissolution of Si into the water has not been observed for the Si wafer having surface covered by the native oxide grown in air. Native oxides grown in air and in ultrapure de‐ionized water have been demonstrated experimentally to exhibit remarkable differences such as contact angles of ultrapure waterdrops and chemical binding energy. These chemical bond structures for native oxide filmsgrown in air and in ultrapure water are also discussed.
803 citations
TL;DR: In this article, the pore size distribution of porous silicon was investigated on different types of substrates and under different experimental conditions, and it was shown that porosity is strongly dependent on the type and resistivity of the original silicon substrate and on the electrochemical parameters used during anodization processes.
Abstract: 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 HF 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. Porous silicon is a material obtained by anodic oxidation of monocrystalline silicon in concentrated hydrofluoric acid solutions. Several papers (1-4) have shown that this material is one of the promising candidates for use in silicon on insulator (SOI) structures in integrated circuit technology. In all the proposed applications, the oxidation properties of porous silicon are used to obtain thick insulating layers of silica in relatively short periods of time. The properties of the material are very dependent on the type and resistivity of the original silicon substrate and on the electrochemical parameters used during the anodization processes. Porous silicon is often characterized by its porosity, mainly due to the existence of a so-called optimal porosity of about 56%, for which good silicon dioxides are obtained with minimum strains and volume expansion (5), which is necessary to obtain fully oxidized structures. However, porosity values alone are not enough to characterize the material as quite different properties can be obtained for materials of the same porosity if the substrate resistivity and preparation conditions are properly chosen. Other parameters to be considered when a better characterization of porous structures is required are pore size and pore size distribution. Both porosity and pore size determine altogether the size of the silicon walls in the porous material, so that properties like crystalline quality (6), optical response (7), thermal behavior (8), and oxidation mechanism (9) are very dependent on both porosity and pore size. It has been shown in a previous paper (10) that it was possible using gas adsorption techniques to determine accurately the pore size and pore distribution of radii in the porous silicon layers. That work was limited to porous silicon layers prepared on (111) heavily P-doped substrates. The aim of the present work is to study (100) substrates and investigate other kinds of resistivity and different electrochemical preparation conditions. Experimental
526 citations