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 article, the phase separation of the layers into SiNCs and surrounding oxynitride matrix was studied at temperatures of up to 1150°C, and the influence of the annealing temperature on Si-O-Si stretching vibration to higher wave numbers after thermal annaling was investigated by several analytical techniques including variable angle spectroscopic ellipsometry, photoluminescence (PL) spectroscopy, x-ray photoelectron spectrograph, Fourier transform infrared spectrometry (FTIR), and transmission electron microscopy (T
109 citations
TL;DR: In this paper, the authors reported laser oscillation at ∼610 nm in aggregates of ultrasmall elemental Si nanoparticles, which constitutes an important step towards the realization of a laser on a chip, hence optoelectronics integration and optical interconnects.
Abstract: We report laser oscillation at ∼610 nm in aggregates of ultrasmall elemental Si nanoparticles. The particles are ultrabright red emitting, dispersed from bulk Si by electrochemistry. The aggregates are excited by radiation at 550–570 nm from a mercury lamp. Intense directed Gaussian beams, with a threshold, manifest the emission. We observe line narrowing, and speckle patterns, indicating spatial coherence. This microlasing constitutes an important step towards the realization of a laser on a chip, hence optoelectronics integration and optical interconnects.
108 citations
TL;DR: In this paper, the authors reported the preparation of SiO2-embedded silicon nanocrystals (Si-NCs) from the thermal processing of sol−gel polymers derived from trichlorosilane (HSiCl3).
Abstract: We report the preparation of SiO2-embedded silicon nanocrystals (Si-NCs) from the thermal processing of sol−gel polymers derived from trichlorosilane (HSiCl3). Straightforward addition of water to HSiCl3 generates a cross-linked (HSiO1.5)n sol−gel polymer suitable for the generation of bulk quantities of SiO2-embedded Si-NCs. It is shown that structural differences between the present (HSiO1.5)n polymer and hydrogen silsesquioxane (HSQ) result in controllable differences in the resulting oxide-embedded Si-NCs produced from these precursors. A polymer structure/NC size relationship is further delineated through the preparation and evaluation of methyl-modified (HSiO1.5)n(CH3SiO1.5)m (m ≪ n, m + n = 1) sol−gel copolymers, in which a low concentration of methyl groups acts as a polymer network modifier and influences the formation of Si-NCs during thermal processing. Si-NC size is readily tailored by controlled variations to peak processing temperature for (HSiO1.5)n and composition (n and m) for (HSiO1.5)n(...
108 citations
TL;DR: In this article, a survey of the physical processes that determine the linear and nonlinear optical properties of nanocomposite materials is presented, with a focus on the nonlinear susceptibility of composite materials.
Abstract: This paper reviews some of the authors' recent research aimed at obtaining an understanding of the physical processes that determine the linear and nonlinear optical properties of nanocomposite materials. One result of this research is the prediction and experimental verification that under proper conditions two materials can be combined in such a manner that the nonlinear susceptibility of the composite exceeds those of the constituent materials. This paper also presents a survey of the various geometrical structures of composite materials. A common approach to the development of nonlinear optical materials entails searching for materials that possess, at the molecular level, desirable nonlinear optical properties. An alternative approach, which will be explored in this paper, entails combining known materials into a composite material. Under proper conditions, this composite material might combine the more desirable properties of the starting materials, or ideally, might possess properties superior to those of the starting materials. Some of the commonly encountered structures of composite materials are shown in figure 1. The Maxwell Garnett (1) geometry consists of small inclusion particles embedded in a host material. The Bruggeman (2) geometry consists of two intermixed components. These two model geometries are the structures most often encountered in theoretical discussions of composite materials. Two additional structures are that of porous silicon and that of layered materials. Recent research (3) has shown that an electrochemical etching procedure can be used to turn silicon into a porous structure. The resulting structure then contains 'worm holes' which can be modelled as cylindrical columns in which the silicon has been eaten away from the host material. When still more material has been eaten away, the resulting structure can be modelled as cylindrical columns of silicon surrounded by voids. In either case, the voids can be filled with a second material to form a composite structure. These composite materials can be thought of as a two-dimensional version of the Maxwell Garnett structure. Research on porous silicon is still quite new and will not be discussed further in this paper. The final structure illustrated in figure 1 is the layered geometry, consisting of alternating layers of two materials with different linear and nonlinear optical properties. In all of the structures shown in figure 1, we assume that the two materials are intermixed on a distance scale much smaller than an optical wavelength. Under these conditions, the propagation of light can be described by effective values of the optical constants that are obtained by performing a suitable volume average of the local optical response of the material. In fact, performing such an average can be rather subtle for situations involving the nonlinear optical response, because it is the nonlinear polarization that must be averaged, and the nonlinear polarization depends on the spatially inhomogeneous electric field amplitude
108 citations
01 May 1998-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, both elemental and compound semiconductor nanocrystals have been formed in insulators by ion beam synthesis, which give rise to strong optical absorption and intense photoluminescence (PL).
Abstract: Both elemental and compound semiconductor nanocrystals have been formed in insulators by ion beam synthesis. Si nanocrystals in SiO2 give rise to strong optical absorption and intense photoluminescence (PL). The dose dependence of optical absorption provides evidence for size dependent changes in the Si nanocrystal bandgap due to quantum confinement, but the PL results suggest that surface or defect states play an important role in PL. CdS and CdSe nanocrystals have been formed in SiO2 and in Al2O3. Their structure, size, and optical properties are discussed.
108 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