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 authors proposed to use Si nanocrystallites, nanowires, and alloying with Ge and crystal strain methods to achieve the carrier confinement required to boost radiative recombination efficiency.
Abstract: Research on efficient light emission from silicon devices is moving toward leading-edge advances in components for nano-optoelectronics and related areas. A silicon laser is being eagerly sought and may be at hand soon. A key advantage is in the use of silicon-based materials and processing, thereby using high yield and low-cost fabrication techniques. Anticipated applications include an optical emitter for integrated optical circuits, logic, memory, and interconnects; electro-optic isolators; massively parallel optical interconnects and cross connects for integrated circuit chips; lightwave components; high-power discrete and array emitters; and optoelectronic nanocell arrays for detecting biological and chemical agents. The new technical approaches resolve a basic issue with native interband electro-optical emission from bulk Si, which competes with nonradiative phonon- and defect-mediated pathways for electron-hole recombination. Some of the new ways to enhance optical emission efficiency in Si diode devices rely on carrier confinement, including defect and strain engineering in the bulk material. Others use Si nanocrystallites, nanowires, and alloying with Ge and crystal strain methods to achieve the carrier confinement required to boost radiative recombination efficiency. Another approach draws on the considerable progress that has been made in high-efficiency, solar-cell design and uses the reciprocity between photo- and light-emitting diodes. Important advances are also being made with silicon-oxide materials containing optically active rare-earth impurities.
119 citations
TL;DR: The role of hydrogen in enhancing the photoluminescence (PL) yield observed from Si nanocrystals embedded in SiO{sub 2} has been studied in this paper.
Abstract: The role of hydrogen in enhancing the photoluminescence (PL) yield observed from Si nanocrystals embedded in SiO{sub 2} has been studied. SiO{sub 2} thermal oxides and bulk fused silica samples have been implanted with Si and subsequently annealed in various ambients including hydrogen or deuterium forming gases (Ar+4%H{sub 2} or Ar+4%D{sub 2}) or pure Ar. Results are presented for annealing at temperatures between 200 and 1100 C. Depth and concentration profiles of H and D at various stages of processing have been measured using elastic recoil detection. Hydrogen or deuterium is observed in the bulk after annealing in forming gas but not after high temperature (1100 C) anneals in Ar. The presence of hydrogen dramatically increases the broad PL band centered in the near-infrared after annealing at 1100 C but has almost no effect on the PL spectral distribution. Hydrogen is found to selectively trap in the region where Si nanocrystals are formed, consistent with a model of H passivating surface states at the Si/SiO{sub 2} interface that leads to enhanced PL. The thermal stability of the trapped H and the PL yield observed after a high temperature anneal have been studied. The hydrogen concentration and PL yield are unchanged for subsequent anneals up to 400 C. However, above 400 C the PL decreases and a more complicated H chemistry is evident. Similar concentrations of H or D are trapped after annealing in H{sub 2} or D{sub 2} forming gas; however, no differences in the PL yield or spectral distribution are observed, indicating that the electronic transitions resulting in luminescence are not dependent on the mass of the hydrogen species.
119 citations
TL;DR: In this paper, a sensitive porous silicon (PS) gas sensor which utilizes photoluminescence induced electroless metallization as a means of obtaining a highly efficient electrical contact has been demonstrated for the detection of HCl, NH3, and NO at the 10 ppm level.
Abstract: The development of a sensitive porous silicon (PS) gas sensor which utilizes photoluminescence induced electroless metallization as a means of obtaining a highly efficient electrical contact has been demonstrated for the detection of HCl, NH3, and NO at the 10 ppm level. The problem of spreading resistance (kΩ–MΩ) is overcome as low resistance contacts ∼20–100 Ω are made to the mesoporous PS structure through electroless gold plating. The response of this device, which operates at a bias voltage of 1–10 mV, is rapid and reversible.
118 citations
TL;DR: In this paper, a novel electrical sensor platform containing a porous silicon (PSi) layer on a crystalline silicon substrate has been developed in which the electrical contacts are made exclusively on the backside of the substrate allowing complete exposure of the surface to the sensing molecules.
Abstract: A novel electrical sensor platform containing a porous silicon (PSi) layer on a crystalline silicon substrate has been developed in which the electrical contacts are made exclusively on the backside of the substrate allowing complete exposure of the surface to the sensing molecules. The PSi layers were 20 μm thick with an average pore diameter of 1 μm. Real-time measurements of capacitance (C) and conductance (G) were performed and the response produced by the addition of different organic solvents was evaluated. The observed response is attributed to the combined effect of a change in dielectric constant inside the porous matrix and a modification in the depletion layer width in the crystalline silicon structure. A space charge region modulation model was used to explain the effect induced by molecules of different dipole moments, dielectric constants, polarizabilities and water solubilities.
118 citations
TL;DR: In this paper, the photoluminescence (PL) was quenched upon immersion in ionic solutions of Cu, Ag, and Au, but not noticeably quenchched in other ionic solution.
Abstract: Various metals were deposited on luminescent porous silicon (PS) by immersion in metal ion solutions and by evaporation. The photoluminescence (PL) was quenched upon immersion in ionic solutions of Cu, Ag, and Au but not noticeably quenched in other ionic solutions. Evaporation of 100 A of Cu or 110 A of Au was not observed to quench PL. Auger electron spectroscopy performed on samples quenched and then immediately removed from solution showed a metallic concentration in the PS layer of order 10 at.%, but persisting to a depth of order 3000 A.
118 citations
References
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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