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 situ boron-doped amorphous hydrogenated silicon films have been anodized in hydrofluoric acid solutions and subsequently electrochemically oxidized in an aqueous electrolyte as mentioned in this paper.
57 citations
TL;DR: In this article, macroporous silicon was used to increase the surface exchange between pore surface and electrolyte and achieved a unit cell capacitance of 320 µF/cm2.
Abstract: In this study, we have demonstrated the possibility of using macroporous silicon electrodes in electrochemical capacitors. Macroporous silicon was used to increase the surface exchange between pore surface and electrolyte. The inherent resistivity of the porous silicon can be reduced through the use of subsequent doping and metallization processes of the macropore surface. A systematic study of the electrolyte concentration and the porous silicon depth influences was also performed. A unit cell capacitance value of 320 µF/cm2 was obtained with doped and metallized p-type macroporous silicon electrodes. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
57 citations
01 Jan 2002
TL;DR: In this article, the dependence of the energy gap between the valence and conduction bands is investigated for divalent metals, and two models are used for their description: tight-binding model and the electron-shell model.
Abstract: Publisher Summary The energy gap between the valence and conduction band is of fundamental importance for the properties of a solid. Most of a material's behavior—such as intrinsic conductivity, optical transitions, or electronic transitions—depends on it. Any change of the gap may significantly alter the material's physics and chemistry. This occurs when the size of a solid is reduced to the nanometer length scale. Therefore, the science and the technology of nano materials need to take into account a band gap, which is different from that of the bulk. This chapter determines experimentally and theoretically the dependence of the energy gap for particles, which are reduced in size to the nanometer range. In addition, effects such as structural changes, lattice contraction, atomic relaxation, surface reconstruction, surface passivation, or strain induced by a host material can change the gap. For clusters of simple metals, two models are used for their description: the tight-binding model and the electron-shell model. They can lead to different band gaps for small clusters and different critical sizes for the cluster-to-bulk transition. For divalent metals, a band gap is expected to open with decreasing particle size because of narrowing and shift of energy bands.
57 citations
TL;DR: In this paper, white electroluminescence (EL) was observed from hydrogenated amorphous-SiNx-based light-emitting device Silicon nitride thin films were deposited on the indium-tin-oxide (ITO)-coated glass substrate by plasma enhanced chemical vapor deposition method with a mixture of Ar-diluted 5% SiH4 and pure N2 gases, in the ratio 2 to 1 Measured x value of the film is 056, and corresponding photoluminecence of aSiN056:H thin
Abstract: White electroluminescence (EL) was observed from hydrogenated amorphous-SiNx-based light-emitting device Silicon nitride thin films were deposited on the indium-tin-oxide (ITO)-coated glass substrate by plasma enhanced chemical vapor deposition method with a mixture of Ar-diluted 5% SiH4 and pure N2 gases, in the ratio 2 to 1 Measured x value of the film is 056, and the corresponding photoluminescence of a-SiN056:H thin film exhibited a red-infrared spectrum, centered at 630 nm The layer structure of the EL device is ITO/a-SiN056:H (80 nm)/Al, with light emitting from the ITO layer, recognizable by the naked eye in the dark, under the 14 V forward bias conditions White EL spectra from ∼400 to 750 nm, with a central peak at 560 nm, were observed in the hydrogenated amorphous silicon nitride EL device A carrier transport mechanism was suggested, and the EL was attributed to the recombination of carriers through the luminescent states
57 citations
TL;DR: In this article, a combination of current transport and charge trapping studies is carried out on a number of samples with varied structural configuration, and it is shown that at low electric fields, trapping of injected carriers dominates, if the coupling between the silicon nanocrystals is strong.
Abstract: Size-controlled silicon nanocrystals in silicon oxynitride matrix were prepared using plasma-enhanced chemical vapor deposition following the superlattice approach. A combination of current transport and charge trapping studies is carried out on a number of samples with varied structural configuration. We demonstrate that at low electric fields, trapping of injected carriers dominates, if the coupling between the silicon nanocrystals is strong. In contrast, we show that at higher electric fields, the charge distribution within the films is essentially governed by charge separation within the superlattice. This effect can be well explained by a two-step electric field ionization of silicon nanocrystals that proceeds via defect-assisted band-to-band tunneling of silicon valence electrons to the conduction band and is mediated by silicon surface dangling bonds. The defects are dominating the charge transport even if the defect density is reduced to a minimum by efficient hydrogen passivation.
57 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