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, an extended photoluminescence (PL) study of porous silicon is presented, where different PL techniques have been used: continuous wave excited (cw) PL, selectively excited PL, excitation spectroscopy of the PL, time decay of PL, and time resolved PL.
Abstract: An extended photoluminescence (PL) study of porous silicon is presented. Different PL techniques have been used: continuous wave excited (cw) PL, selectively excited PL, excitation spectroscopy of the PL, time decay of the PL, and time resolved PL. These measurements have been performed on a set of samples of various porosities and at various temperatures. Strong experimental evidence is found for the influence of disorder and of dispersive motion of excitons on the recombination dynamics. The data are interpreted in the framework of the trap‐controlled hopping mechanism for the dispersive motion of excitons in a disordered array of Si nanocrystals.
147 citations
TL;DR: In this article, a colloid of ultrabright blue luminescent nanoparticles (1 nm in diameter) was reconstituted into films or microcrystallites, and the results were discussed in terms of population inversion, produced by quantum tunneling or/and thermal activation, and stimulated emission in the quantum confinement-engineered Si-Si phase found only on ultrasmall Si nanoparticles.
Abstract: We dispersed electrochemical etched Si into a colloid of ultrabright blue luminescent nanoparticles (1 nm in diameter) and reconstituted it into films or microcrystallites. When the film is excited by a near-infrared two-photon process at 780 nm, the emission exhibits a sharp threshold near 106 W/cm2, rising by many orders of magnitude, beyond which a low power dependence sets in. Under some conditions, spontaneous recrystallization forms crystals of smooth shape from which we observe collimated beam emission, pointing to very large gain coefficients. The results are discussed in terms of population inversion, produced by quantum tunneling or/and thermal activation, and stimulated emission in the quantum confinement-engineered Si–Si phase found only on ultrasmall Si nanoparticles. The Si–Si phase model provides gain coefficients as large as 103–105 cm−1.
146 citations
TL;DR: In this paper, the chemical modification of high surface area, photoluminescent porous silicon (PSi) by reaction at a moderately elevated temperature (<115 °C) with alkenes (RCHCH2) and aldeh...
Abstract: This paper describes the chemical modification of high surface area, photoluminescent porous silicon (PSi) by reaction at a moderately elevated temperature (<115 °C) with alkenes (RCHCH2) and aldeh...
146 citations
TL;DR: In this paper, the fabrication technology and properties of a light-emitting device including a porous pn junction are presented, employing the selective formation of different kinds of porous silicon substructures caused by the doping level and the illumination during anodization.
Abstract: The fabrication technology and the properties of a light‐emitting device including a porous pn junction are presented. We employ the selective formation of different kinds of porous silicon substructures caused by the doping level and the illumination during anodization. The device has a nanoporous light‐emitting n layer between a mesoporous p+‐doped capping layer and the macroporous n substrate. The pn junction formed in this way has strong rectifying characteristics. It shows bright red‐orange light emission under forward bias. Compared to simple metal‐porous silicon devices, the structure has an increased quantum efficiency (factor 10–100).
146 citations
TL;DR: Treatment of anodized or chemically etched silicon ("porous silicon") with dilute nitric acid or persulfate solution results in weak chemiluminescence in the visible region, suggesting that the visible emission seen with porous Si can be attributed to this substance.
Abstract: Treatment of anodized or chemically etched silicon ("porous silicon") with dilute nitric acid or persulfate solution results in weak chemiluminescence in the visible region. Concentrated nitric acid reacts violently with porous Si produced by anodization with a bright flash of light. The fact that similar reactions occur with siloxene (Si6H6O3) prepared from CaSi2 suggests that the visible emission seen with porous Si can be attributed to this substance.
146 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