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Journal ArticleDOI

Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers

03 Sep 1990-Applied Physics Letters (American Institute of Physics)-Vol. 57, Iss: 10, pp 1046-1048
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
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Journal ArticleDOI
TL;DR: In this article, the possibility of a new blue light emitting diode (LED) using porous SiC as a luminescent material is described, which is electrochemically formed on a single crystalline 6H-SiC substrate fabricated by the Acheson method.
Abstract: The possibility of a new blue light emitting diode (LED) using porous SiC as a luminescent material is described The porous SiC is electrochemically formed on a single crystalline 6H‐SiC substrate fabricated by the Acheson method The diode structure is a Schottky‐like junction between indium tin oxide (ITO) and porous SiC The ITO/porous SiC junction shows a rectification behavior and a blue electroluminescence (EL) under the forward direction

71 citations

Journal ArticleDOI
TL;DR: In this article, it was shown that the fluoride species may be derived from either HF or acidified NH 4 HF 2. But, a large positive electrochemical potential is not a sufficient condition for efficient porous Si production.
Abstract: Stain etching of silicon provides a spontaneous, self-limiting chemical method to produce nanocrystalline silicon films (porous Si). Whereas the existence of etchants capable of producing porous Si has been known for sometime, little has been known concerning how solution composition influences the efficacy of porous Si production and the properties of the resulting films. We demonstrate that the fluoride species may be derived from either HF or acidified NH 4 HF 2 . A range of oxidants may be used as long as their counterions do not lead to precipitation. However, a large positive electrochemical potential is not a sufficient condition for efficient porous Si production. Bubble production, which is deleterious to film homogeneity and long thought to be inherent to the process, can be avoided by the use of transition metal-containing oxidants. Properties of the film, such as morphology, growth rate, porosity, and the wavelength of the photoluminescence maximum, respond to the etchant composition. We observe a blue shift in photoluminescence, which correlates with an increasingly positive electrochemical potential (Eg) of the oxidant. It is argued that Eg plays a role much like wavelength in photoelectrochemical etching and that smaller nanocrystals are produced with more positive values of E 0 .

71 citations

Journal ArticleDOI
TL;DR: In this paper, the dependence of the amount of Cu deposition on Cu2+ concentration, halogen ion concentration, and immersion time was investigated using chelatometric titration, which revealed that metal deposition occurred simultaneously with the oxidation of silicon to SiO2.
Abstract: Metal deposition into a porous silicon (PS) layer by immersion plating has been studied. Ag and Cu were found to deposit on PS, while Ni was found not to deposit. The dependence of the amount of Cu deposition on Cu2+ concentration, halogen ion concentration, and immersion time was investigated using chelatometric titration. Copper deposition from halide solutions exhibited an unusual behavior; the amount increased with increasing concentration, then decreased, and no copper deposited at high concentration. This is because adsorption of chloride and bromide ions inhibits the copper deposition process. We have also discussed the metal deposition mechanism on the basis of x-ray diffraction, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy measurements. They revealed that metal deposition occurred simultaneously with the oxidation of silicon to SiO2. Copper crystals 30–80 nm in diameter deposited on the oxidized PS surface rather than on the unoxidized PS surface.

70 citations

Journal ArticleDOI
TL;DR: A selection of theoretical efforts and experimental surface engineering approaches are highlighted and recent surface engineering results that have utilized novel plasma-liquid interactions are focused on.
Abstract: Quantum confined silicon nanocrystals (Si-ncs) exhibit intriguing properties due to silicon's indirect bandgap and their highly reactive surfaces. In particular the interplay of quantum confinement with surface effects reveals a complex scenario, which can complicate the interpretation of Si-nc properties and prediction of their corresponding behaviour. At the same time, the complexity and interplay of the different mechanisms in Si-ncs offer great opportunities with characteristics that may not be achievable with other nano-systems. In this context, a variety of carefully surface-engineered Si-ncs are highly desirable both for improving our understanding of Si-nc photo-physics and for their successful integration in application devices. Here we firstly highlight a selection of theoretical efforts and experimental surface engineering approaches and secondly we focus on recent surface engineering results that have utilized novel plasma-liquid interactions.

70 citations

Journal ArticleDOI
TL;DR: The optical properties of porous GaAs formed electrochemically on n-and p-type GaAs in HCl electrolyte are reported in this article, where the porous structure comprises GaAs crystallites ranging in size from micrometers to nanometers.
Abstract: The optical properties of porous GaAs formed electrochemically on n- and p-type GaAs in HCl electrolyte are reported. The porous structure comprises GaAs crystallites ranging in size from micrometers to nanometers and under certain chemical conditions other transparent crystallites of As 2 O 3 and Ga 2 O 3 form. Photoluminescence (PL) measurements at 295 K reveal an “infrared” PL at ∼840 nm and a “green” PL at ∼ 540 nm, which could easily be seen by the naked eye in some samples. The infrared and green PL peak wavelength and intensity varied from sample to sample consistent with an assignment to quantum confinement effects in GaAs micro- and nanocrystallites, respectively.

70 citations

References
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Journal ArticleDOI
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

Journal ArticleDOI
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

Journal ArticleDOI
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

Journal ArticleDOI
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