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 optical properties of semiconductor and insulator nanocomposites, including porous materials such as silicon, gallium phosphide, aluminum oxide, and structures based on them, were investigated.
Abstract: We consider the optical properties of semiconductor – insulator and insulator – insulator nanocomposites, including porous materials such as silicon, gallium phosphide, aluminum oxide, and structures based on them. The main focus is on the effect of form birefringence, which is caused by the anisotropy of pores in the materials under study. The applicability of the effective medium model for describing the optical properties of nanocomposites is discussed. The effects of light localization due to the scattering of light in such inhomogeneous media are analyzed.
129 citations
TL;DR: In this paper, the reaction of nanocrystalline (porous) silicon with phenyllithium and lithium phenylacetylide results in functionalization of the silicon surface with phenyl and phenyl-acetylene moieties, respectively.
Abstract: Reaction of nanocrystalline (“porous”) silicon with phenyllithium and lithium phenylacetylide results in functionalization of the silicon surface with phenyl and phenylacetylene moieties, respectively. The reaction proceeds by addition of the aryllithium reagent across a surface Si−Si bond, resulting in a Si−aryl bond and Si−Li species. The highly reactive Si−Li surface species is readily hydrolyzed by water, resulting in significant surface oxidation. The surface-bound Li can also be replaced with H or acyl species by addition of trifluoroacetic acid, acetyl chloride, heptanoyl chloride, or 4-butylbenzoyl chloride. These latter treatments significantly reduce the rate of air oxidation of the porous silicon surface. The nanocrystalline silicon samples used display visible photoluminescence arising from quantum confinement effects. Functionalization with phenyllithium preserves some of the photoluminescence, while the lithium phenylacetylide reaction results in almost complete loss of photoluminescence fro...
129 citations
TL;DR: It is demonstrated that electrochemical size reduction can be used for precisely controlled fabrication of silicon nanowires of widths approaching the 10 nm regime and it is proposed that charged surface states play a more pronounced role as the nanowire cross-sectional dimensions decrease.
Abstract: We demonstrate that electrochemical size reduction can be used for precisely controlled fabrication of silicon nanowires of widths approaching the 10 nm regime. The scheme can, in principle, be applied to wires defined by optical lithography but is here demonstrated for wires of ∼100−200 nm width, defined by electron beam lithography. As for electrochemical etching of bulk silicon, the etching can be tuned both to the pore formation regime as well as to electropolishing. By in-situ optical and electrical characterization, the process can be halted at a certain nanowire width. Further electrical characterization shows a conductance decreasing faster than dimensional scaling would predict. As an explanation, we propose that charged surface states play a more pronounced role as the nanowire cross-sectional dimensions decrease.
128 citations
TL;DR: Based on a thermodynamic model for size-dependent melting temperature, the sizedependent band-gap of low dimensional semiconductor compounds is modeled without any adjustable parameter as discussed by the authors, and the model predicts an increase of the bandgap of nanoparticles and nanowires for IIB-VIB and IIIB-VB compounds, with decreasing their size.
128 citations
Patent•
24 Jan 2005TL;DR: In this paper, the contact resistance between the porous silicon region and the front contact is between about 10 ohms and 100 ohms, where the front contacts are disposed thereon.
Abstract: A sensor is disclosed. A representative sensor includes a silicon substrate having a porous silicon region. A portion of the porous silicon region has a front contact is disposed thereon. The contact resistance between the porous silicon region and the front contact is between about 10 ohms and 100 ohms.
128 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