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.
Citations
More filters
TL;DR: In this paper, Nanoporous GaN films are prepared by UV assisted electrochemical etching using HF solution as an electrolyte and micro-photoluminescence (PL), micro-Raman scattering, and scanning electron microscopy (SEM) techniques have been employed to assess the optical quality and morphology of these nanoporous films, and an average pore size of about 85-90 nm with a transverse dimension of 70-75 nm.
Abstract: — — Nanoporous GaN films are prepared by UV assisted electrochemical etching using HF solution as an electrolyte. To assess the optical quality and morphology of these nanoporous films, micro-photoluminescence (PL), micro-Raman scattering, scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques have been employed. SEM and AFM measurements revealed an average pore size of about 85-90 nm with a transverse dimension of 70-75 nm. As compared to the as-grown GaN film, the porous layer exhibits a substantial photoluminescence intensity enhancement with a partial relaxation of compressive stress. Such a stress relaxation is further confirmed by the red shifted E 2 (TO) phonon peak in the Raman spectrum of porous GaN.
58 citations
TL;DR: Using both elastic-recoil detection analysis and secondary ion mass spectroscopy, it was concluded that B atoms are not removed from the porous layer as mentioned in this paper, which is not the case for most porous samples.
Abstract: Highly-doped p-type Si is electrochemically etched in an HF-based electrolyte to produce mesoporous surface layers. Using both elastic-recoil detection analysis and secondary ion mass spectroscopy it is concluded that B atoms are not removed from the porous layer. Crystallite size for the most porous samples is related to the average dopant spacing. It is argued that the electrolytic erosion of Si stops when B is in the surface layer and passivated.
58 citations
TL;DR: In this article, the Si-cluster assembled films cannot be simply interpreted on the basis of quantum confinement effects and are rather attributed to the presence of odd-membered rings in the incident-free cluster structure.
Abstract: Nanosize neutral silicon clusters produced using a laser vaporization source were analyzed in the gas phase and deposited on various substrates at room temperature in ultrahigh vacuum. Nanostructured thin films with thickness around 100 nm resulting from this nearly ballistic deposition process were subsequently characterized by several complementary electron spectroscopy techniques to investigate the electronic structure. The film properties are comparable to those of a disordered phase but different from the properties of conventional amorphous or nanoporous silicon. The specific features observed in the Si-cluster assembled films cannot be simply interpreted on the basis of quantum confinement effects and are rather attributed to the presence of odd-membered rings in the incident-free cluster structure. Some Si-cluster geometries in the subnanometric size range are proposed and discussed on the basis of the experimental results and a tight binding scheme.
58 citations
TL;DR: In this paper, the surface chemical composition and the effect of electron-beam irradiation has been investigated through Auger spectroscopy, showing that the Si LVV Auger transition dominates the spectrum, even in aged samples.
Abstract: Light‐emitting porous silicon films have been obtained by anodic etching p‐type Si samples in a HF‐ethanol solution. Porous Si samples efficiently luminesce at room temperature in the visible region. A degradation of the luminescence intensity with time is observed. Micro‐Raman spectroscopy of free‐standing porous silicon layers indicates phonon confinements as well as a strong laser heating effects. The surface chemical composition and the effect of electron‐beam irradiation has been investigated through Auger spectroscopy. The Si LVV Auger transition dominates the spectrum, even in aged samples. The Si line shape gives evidence of a covalent bond between the porous Si surface atoms and some adsorbed species. A prolonged electron irradiation results in a strong variation of the surface chemical composition, with an anomalous carbon accumulation. Gold thin films have been deposited on the porous Si surface to form metal‐semiconductor junctions. Schottky diodes with large rectifying ratio, ideality factor,...
58 citations
TL;DR: In this paper, the selective modification of porous silicon conductometric gas sensors for phosphine detection was discussed, where Tin, nickel, copper and gold were electrolessly deposited onto nanopore covered microporous porous silicon surfaces forming SnOx, NiO, CuxO and AuxO nanostructured centers.
Abstract: We discuss the selective modification of porous silicon (PS) conductometric gas sensors for phosphine detection. Tin, nickel, copper and gold are electrolessly deposited onto nanopore covered microporous porous silicon surfaces forming SnOx, NiO, CuxO and AuxO nanostructured centers. Further studies have also been carried out with nanostructured alumina coated porous silicon. The porous silicon surface is analyzed for the metal oxides considered using XPS measurements. These experiments demonstrate that the indicated metals are deposited to the nanopore covered micropores of the PS interface and are oxidized to form metal oxide sites. The sensitivity change of these modified porous silicon gas sensor surfaces has been measured under 1–5 ppm PH3 exposure. An improved sensitivity, of the order of 5 times that of untreated porous silicon, for 1 ppm exposure is observed. The selection of the nanostructure deposition is based on the hard to soft acid character of the nanostructured deposit and its subsequent effect on the physisorption of PH3, an intermediate base. The observed behavior follows an inverse pattern IHSAB to the hard soft acid–base concept.
58 citations
References
More filters
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