Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers
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.
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TL;DR: In this paper, the authors observed a synchronous modulation of the diameters of pores on large areas of the samples which indicates a correlation between the phases of the oscillations in the pores.
Abstract: Voltage oscillations were observed during anodic etching of 100 -oriented n-InP substrates in an aqueous solution of HCl at high constant current density. Under certain conditions, the oscillations lead to a synchronous modulation of the diameters of pores on large areas of the samples which indicates a correlation between the phases of the oscillations in the pores. These self-induced diameter oscillations may be useful for three-dimensional microstructuring of n-InP and thus for the design and fabrication of new photonic materials. © 2001 The Electrochemical Society. DOI: 10.1149/1.1370417 All rights reserved.
60 citations
TL;DR: In this article, a room temperature visible light emitting diodes based on porous silicon planar microcavities are reported. The electrical injection was provided by metal contacts (Schottky-like diode) and the performance of these structures with respect to standard porous silicon LEDs is presented and discussed.
60 citations
TL;DR: In this article, a correlation between the co-ordination numbers of the first, second and third Si neighbor shells from Fourier transform fitting of EXAFS and both emission peak energies and optical band gaps estimated by PLE (photoluminescence excitation dependence) suggests that the nanostructures of the newly produced red, yellow and green emitting porous Si specimens are nanowires, rather than nanocrystalline.
Abstract: Freshly produced red, yellow and green emitting porous Si specimens have been studied by NEXAFS and EXAFS (near edge and extended x‐ray absorption fine structure). The emission peaks are at 690, 580, and 520 nm, which almost covers the full visible range that direct anodization can achieve. The correlation between the co‐ordination numbers of the first, second and third Si neighbor shells from Fourier transform fitting of EXAFS and both emission peak energies and optical band gaps estimated by PLE (photoluminescence excitation dependence) suggests that the nanostructures of the PS are nanowires, rather than nanocrystalline. Two types of quantum nanowire with one and one‐plus‐a‐fraction dimensionality are proposed to interpret the correlation. The order factors of the theoretical fits suggest the nanowires of the freshly produced PS have crystalline cores.
60 citations
TL;DR: In this paper, the electron storage occurs in the SiO2/Ge/SiO2 potential well via electron tunneling into the oxide film and the flatband voltage shifts to 091 V after the electron injection.
Abstract: SiO2/Ge nanocrystal/SiO2 structures have been fabricated by deposition of Ge film on a SiO2 layer and subsequent oxidation of the structure at a temperature between 800 °C and 1000 °C Secondary ion mass spectrometry results indicate that the Ge precipitates into the bulk SiO2 at a density of 1×1012 cm−2 Raman spectra show a sharp peak at 300 cm−1 for the nanocrystallized Ge The nanocrystal diameter is determined to be 5 nm on average In the metal–insulator–silicon structure, electron storage occurs in the SiO2/Ge/SiO2 potential well via electron tunneling into the oxide film Capacitance-voltage measurements indicate that flatband voltage (VFB) shifts to 091 V after the electron injection The VFB shift is attributed to the charge storing for a single electron per potential well
59 citations
TL;DR: In this article, the pore walls of a porous silicon membrane were grafted with molecules bearing acid groups to mimic the structure of an ionomer, such as Nafion®, to obtain an inorganic, dimensionally stable, proton-conducting membrane.
Abstract: Nowadays the rise in portable electronics requires energy sources compatible with the environmental constraints. We demonstrate, in this paper, how microfabrication techniques allow the development of low-cost miniature fuel cells fully integrated on silicon. Contrary to usual proton-conducting membranes made of ionomers ensuring the proton conductivity of proton-exchange membrane fuel cells (PEMFCs), we present here another way to proceed. It consists in the chemical grafting of molecules bearing acid groups on the pore walls of a porous silicon membrane to mimic the structure of an ionomer, such as Nafion®. We obtain an inorganic, dimensionally stable, proton-conducting membrane with many optimizable parameters such as the pore size and the pore structure of the membrane or the nature of the grafted molecules. Moreover, the use of a silicon substrate offers advantages of serial and parallel integration, the possibility of encapsulation by wafer bonding and gas feed and electrical contacts may be included into the membrane etching process, thanks to simple KOH wet etching processes and metal sputtering.
59 citations
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TL;DR: In this article, the properties of electrolyte-semiconductor barriers are described, with emphasis on germanium, and the use of these barriers in localizing electrolytic etching is discussed.
Abstract: Properties of electrolyte-semiconductor barriers are described, with emphasis on germanium. The use of these barriers in localizing electrolytic etching is discussed. Other localization techniques are mentioned. Electrolytes for etching germanium and silicon are given.
1,039 citations
TL;DR: It is found that a standard, widespread, chemical-preparation method for silicon, oxidation followed by an HF etch, results in a surface which from an electronic point of view is remarkably inactive, which has implications for the ultimate efficiency of silicon solar cells.
Abstract: We have found that a standard, widespread, chemical-preparation method for silicon, oxidation followed by an HF etch, results in a surface which from an electronic point of view is remarkably inactive. With preparation in this manner, the surface-recombination velocity on Si111g is only 0.25 cm/sec, which is the lowest value ever reported for any semiconductor. Multiple-internal-reflection infrared spectroscopy shows that the surface appears to be covered by covalent Si-H bonds, leaving virtually no surface dangling bonds to act as recombinatiuon centers. These results have implications for the ultimate efficiency of silicon solar cells.
910 citations
TL;DR: In this paper, multiple internal infrared reflection spectroscopy has been used to identify the chemical nature of chemically oxidized and subsequently HF stripped silicon surfaces, and these very inert surfaces are found to be almost completely covered by atomic hydrogen.
Abstract: Multiple internal infrared reflection spectroscopy has been used to identify the chemical nature of chemically oxidized and subsequently HF stripped silicon surfaces. These very inert surfaces are found to be almost completely covered by atomic hydrogen. Results using polarized radiation on both flat and stepped Si(111) and Si(100) surfaces reveal the presence of many chemisorption sites (hydrides) that indicate that the surfaces are microscopically rough, although locally ordered. In particular, the HF‐prepared Si(100) surface appears to have little in common with the smooth H‐saturated Si(100) surface prepared in ultrahigh vacuum.
588 citations
TL;DR: In this article, the authors measured hydrogen desorption from monohydride and dihydride species on crystalline-silicon surfaces using transmission Fourier-transform infrared (FTIR) spectroscopy.
Abstract: Hydrogen desorption kinetics from monohydride and dihydride species on crystalline-silicon surfaces were measured using transmission Fourier-transform infrared (FTIR) spectroscopy. The FTIR desorption measurements were performed in situ in an ultrahigh-vacuum chamber using high-surface-area porous-silicon samples. The kinetics for hydrogen desorption from the monohydride and dihydride species was monitored using the SiH stretch mode at 2102 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and the ${\mathrm{SiH}}_{2}$ scissors mode at 910 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, respectively. Annealing studies revealed that hydrogen from the ${\mathrm{SiH}}_{2}$ species desorbed between 640 and 700 K, whereas hydrogen from the SiH species desorbed between 720 and 800 K. Isothermal studies revealed second-order hydrogen desorption kinetics for both the monohydride and dihydride surface species. Desorption activation barriers of 65 kcal/mol (2.82 eV) and 43 kcal/mol (1.86 eV) were measured for the monohydride and dihydride species, respectively. These desorption activation barriers yield upper limits of 84.6 kcal/mol (3.67 eV) and 73.6 kcal/mol (3.19 eV) for the Si-H chemical bond energies of the SiH and ${\mathrm{SiH}}_{2}$ surface species.
479 citations