Electroless Ni plating on n- and p-type porous Si for ohmic and rectifying contacts
TL;DR: In this article, the properties of electrical contacts made on porous Si by the electroless Ni plating technique have been studied and it is shown that due to the pore infiltration property of the plating solution, metallization occurs inside the pores over an effective area several times higher than the physical area of the sample.
Abstract: The properties of electrical contacts made on porous Si by the electroless Ni plating technique have been studied. It is shown that due to the pore infiltration property of the plating solution, metallization occurs inside the pores over an effective area several times higher than the physical area of the sample. By making variations in the plating bath composition, Ni containing a small amount of P or B as an impurity is plated and excellent ohmic or rectifying contacts on n- or p-type porous Si are obtained. It is further observed that a higher area of contact with comparatively superior electrical properties is obtained when electroless Ni plating is made from the bath which introduces B as the impurity.
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TL;DR: In this paper, the authors used titania-silica in photocatalytic process as an alternative to the conventional TiO2 catalysts, and the synthesized samples are characterized by X-ray diffraction, UV-Vis spectroscopy, Fourier transform infrared spectrography, Brunauett-Emmett-Teller and field-dependent photoconductivity.
Abstract: The use of titania–silica in photocatalytic process has been proposed as an alternative to the conventional TiO2 catalysts. Mesoporous materials have been of great interest as catalysts because of their unique textural and structural properties. Mesoporous TiO2, SiO2 nanoparticles and TiO2/SiO2 nanocomposites were successfully synthesized by sol–gel method using titanium (IV) isopropoxide, tetra-ethylorthosilicate as starting materials. The synthesized samples are characterized by X-ray diffraction, UV–Vis spectroscopy, Fourier transform infrared spectroscopy, Brunauett–Emmett–Teller and field-dependent photoconductivity. The UV–Vis spectrum of as-synthesized samples shows similar absorption in the visible range. The crystallite size of the as-synthesized samples was calculated by Scherrer’s formula. The BET surface area for TiO2/SiO2 nanocomposite is found to be 303 m2/g and pore size distribution has average pore diameter about 10 nm. It also confirms the absence of macropores and the presence of micro and mesopores. The field-dependent photoconductivity of TiO2/SiO2 nanocomposite shows nearly 300 folds more than that of TiO2 nanoparticle for a field of 800 V/cm.
87 citations
Cites background from "Electroless Ni plating on n- and p-..."
...linear increase of current in the dark and visible light-illuminated samples in all the three cases with increase in applied field depicting the ohmic nature of the contacts (Dhar and Chakrabarti 1996)....
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...The plot indicates a linear increase of current in the dark and visible light-illuminated samples in all the three cases with increase in applied field depicting the ohmic nature of the contacts (Dhar and Chakrabarti 1996)....
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TL;DR: In this paper, various composite structures that have been formed from porous silicon layers in recent years are reviewed, by focusing on the different methods used for deposition: dry processes, impregnation by contact with a liquid, chemical bath deposition or electrochemical deposition.
Abstract: The open porous structure and the very large specific surface area of porous silicon have motivated scientists to introduce different materials into the pores, forming composite structures devoted to different applications relying on the luminescence properties or the sensing capability of the resulting nanostructures. In this paper, the various composite structures that have been formed from porous silicon layers in recent years are reviewed, by focusing on the different methods used for deposition: dry processes, impregnation by contact with a liquid, chemical bath deposition or electrochemical deposition. Special attention is given to the particular requirements and specific drawbacks of each process.
67 citations
TL;DR: In this article, a polarization parameter was defined to describe the effects of the interfacial kinetics and diffusion on the uniformity of displacement deposition of nickel with the porous Si skeleton of the PS in an aqueous solution containing nickel ions and fluoride.
Abstract: With its potential applications in displays and sensors, 1 there has been significant interest in metal deposition into porous silicon PS for use as electrical contacts to the PS-based devices. 2-14 Metalized porous Si has also been shown to be an effective way to engineer the Si substrate impedance for microwave crosstalk isolation in mixedsignal integrated circuits. 15 Many approaches have been experimented for depositing metals into porous Si including dry processes, impregnation by contact with a liquid, chemical bath deposition, and electrochemical deposition. None of these were able to achieve deposition into high aspect ratio pores with most of the metal being deposited at the pore openings near the surface of the porous Si film. 2 The studies utilizing wet processes were often focused on the feasibility of plating bath chemistries and deposition mechanism. 3-6,11-14,16 The PS films used in these studies have thickness ranging from 0.5 to 15 m with the maximum demonstrated depth of deposition being 1.3 m. 5-8,11-13 A deposition process that allows uniform deposition of metal into high aspect ratio of up to 200 pores will have a significant impact on technology. Previously, we conducted theoretical investigation into the uniformity of displacement deposition of nickel with the porous Si skeleton of the PS in an aqueous solution containing nickel ions and fluoride. 17 The distribution of nickel along the depth of the pores was treated as a current distribution issue. It was found that both the interfacial kinetics and mass transfer have great influence on the nickel deposition uniformity, and that the interfacial kinetics varies considerably with deposition time. A polarization parameter was defined to describe the effects of the interfacial kinetics and diffusion. The parameter incorporates all the properties of the displacement deposition system and represents a measure of Ni 2+ interfacial reaction rate relative to its diffusion rate toward the pore bottom. The deposition distribution along the pore depth exhibits a strong dependence on the polarization parameter . High values of correspond to the mass transfer limitation leading to non-uniform deposition distribution, while small gives uniform deposition where the process is dominated by the interfacial reaction kinetics. Nonuniform deposition essentially occurs at the initial stage where the process is accompanied by a high deposition rate and nonuniform Ni 2+ concentration distribution. As the deposition process continues, the initial nonuniform deposition becomes progressively more uniform due to reduced deposition rate and consequent shift of the process from the mass transfer limitation to the interfacial reaction control. It was predicted that the nonuniformity at the initial stage could be remedied by increasing the bulk concentration of nickel ions and decreasing the plating bath pH. Introduction of leveling additive coumarin to the plating solution was also shown to significantly improve the uniformity. This paper presents the results of experimental studies on the behavior of nickel displacement deposition into PS and the dependence of the uniformity on plating bath chemistry. The experimental observations are consistent with the theoretical analyses and predictions made in the previous study. Very uniform deposition is attained at greatly reduced deposition time. Experimental
34 citations
TL;DR: In this article, a modified sol-gel method was used to extract titania (TiO2), silica (SiO2) nanoparticles, and binary TiO2-SiO 2 nanocomposites with various molar ratios of silica contents.
Abstract: Sole components of titania (TiO2), silica (SiO2) nanoparticles, and binary TiO2–SiO2 nanocomposites with various molar ratios of silica contents were prepared by modified sol–gel method. The samples were calcined at 500 °C for 5 h and characterized by X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy, Brunauett–Emmett–Teller (BET), and photoconductivity. The crystallite size for TiO2/SiO2 nanocomposites was calculated using Scherrer’s formula and found to be 5 nm for TiO2 nanoparticles. The binary oxide shows the anatase type of TiO2 at the mole ratio up to 80 mol% of TiO2 added. The band gap for as-synthesized nanocomposites was calculated and it was found that the band gap decreases with increase of SiO2 content and then decreases with excess SiO2 content. FTIR confirms that both TiO2 and SiO2 phases have been formed. The BET surface area for TiO2/SiO2 nanocomposite is found to be 303 m2/g, and pore size distribution has an average pore diameter about 10 nm for 40 mol% of TiO2 added. It also confirms the absence of macropores and the presence of micro and mesopores. The field-dependent dark and photoconductivity studies reveal that the dark and photocurrent increase linearly with applied field confirming the ohmic nature of the electric contacts. The dark and photocurrent increase slightly with increase of SiO2 content and decrease with excess amount of SiO2.
32 citations
31 citations
References
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TL;DR: In this paper, free standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography using electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers.
Abstract: Indirect evidence is presented that free‐standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography. The novel approach uses electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers. Mesoporous Si layers of high porosity exhibit visible (red) photoluminescence at room temperature, observable with the naked eye under <1 mW unfocused (<0.1 W cm−2) green or blue laser line excitation. This is attributed to dramatic two‐dimensional quantum size effects which can produce emission far above the band gap of bulk crystalline Si.
7,393 citations
TL;DR: In this paper, the formation and properties of porous silicon formed by anodising silicon under a wide range of conditions were investigated and the currentvoltage characteristics of the silicon-hydrofluoric acid system were presented.
Abstract: We report a systematic study of the formation and properties of porous silicon formed by anodising silicon under a wide range of conditions. The current-voltage characteristics of the silicon-hydrofluoric acid system are presented. The detailed microstructure of the two types of porous silicon that form depending on the dopant concentration in the silicon, were determined by cross-sectional transmission electron microscopy. A theory for the formation of porous silicon is proposed which accounts for the dependence of the microstructure on the anodising conditions. The formation of porous gallium arsenide, analogous to porous silicon, is reported for the first time.
477 citations
TL;DR: In this article, a highly sensitive photodetector was made with a metal-porous silicon junction and the spectral response was measured for the wavelength range from 400 nm to 1.075 μm.
Abstract: A highly sensitive photodetector was made with a metal‐porous silicon junction. The spectral response was measured for the wavelength range from 400 nm to 1.075 μm. It was demonstrated that close to unity quantum efficiency could be obtained in the wavelength range of 630–900 nm without any antireflective coating. The detector response time was about 2 ns with a 9 V reverse bias. The possible mechanisms are discussed.
193 citations
TL;DR: In this paper, an all solid state, VLSI compatible, electroluminescent device based on porous silicon with an external quantum efficiency greater than 0.1% under CW operation was presented.
Abstract: The authors report an all solid state, VLSI compatible, electroluminescent device based on porous silicon with an external quantum efficiency greater than 0.1% under CW operation. The emission, which is broadband and peaks at 600 nm, is detected above a low threshold current density and voltage of 0.01 Am-2 and 2.3 V, respectively.
169 citations
145 citations