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, a large-scale synthesis of silicon nanowires (SiNWs) using a simple but effective approach was reported, where high purity SiNWs of uniform diameters around 15 nm were obtained by sublimating a hot-pressed silicon powder target at 1200 °C in a flowing carrier gas environment.
Abstract: We report the large-scale synthesis of silicon nanowires (SiNWs) using a simple but effective approach. High purity SiNWs of uniform diameters around 15 nm were obtained by sublimating a hot-pressed silicon powder target at 1200 °C in a flowing carrier gas environment. The SiNWs emit stable blue light which seems unrelated to quantum confinement, but related to an amorphous overcoating layer of silicon oxide. Our approach can be used, in principle, as a general method for synthesis of other one-dimensional semiconducting, or conducting nanowires.
362 citations
TL;DR: In this article, the photoluminescence of the silicon nanocrystals and their yield were measured as a function of their size, and it was found that the photophotonicity follows very closely the quantum-confinement model.
Abstract: Silicon nanocrystals with diameters between 2.5 and 8 nm were prepared by pulsed CO2 laser pyrolysis of silane in a gas flow reactor and expanded through a conical nozzle into a high vacuum. Using a fast-spinning molecular-beam chopper, they were size-selectively deposited on dedicated quartz substrates. Finally, the photoluminescence of the silicon nanocrystals and their yield were measured as a function of their size. It was found that the photoluminescence follows very closely the quantum-confinement model. The yield shows a pronounced maximum for sizes between 3 and 4 nm.
360 citations
TL;DR: In this article, the metal-assisted chemical etching of silicon, a low-cost and versatile method enabling fine control over morphology feature of silicon nanostructures, is summarized.
359 citations
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12 Dec 2011
TL;DR: Porosity, Pore size, and pore size distribution in the x-y plane using physical or virtual masks were measured in this paper, showing that porosity and thickness of porosity can be measured using lift-off films of Porous Silicon.
Abstract: Preface FUNDAMENTALS OF POROUS SILICON PREPARATION Introduction Chemical Reactions Governing the Dissolution of Silicon Experimental Set-up and Terminology for Electrochemical Etching of Porous Silicon Electrochemical Reactions in the Silicon System Density, Porosity, and Pore Size Definitions Mechanisms of Electrochemical Dissolution and Pore Formation Resume of the Properties of Crystalline Silicon Choosing, Characterizing, and Preparing a Silicon Wafer PREPARATION OF MICRO-, MESO-, AND MACRO-POROUS SILICON LAYERS Etch Cell: Materials and Construction Power Supply Other Supplies Safety Precautions and Handling of Waste Preparing HF Electrolyte Solutions Cleaning Wafers Prior to Etching Preparation of Microporous Silicon from a p-Type Wafer Preparation of Mesoporous Silicon from a p++-Type Wafer Preparation of Macroporous, Luminescent Porous Silicon from an n-Type Wafer (Frontside Illumination) Preparation of Macroporous, Luminescent Porous Silicon from an n-Type Wafer (Back Side Illumination) Preparation of Porous Silicon by Stain Etching Preparation of Silicon Nanowire Arrays by Metal-Assisted Etching PREPARATION OF SPATIALLY MODULATED POROUS SILICON LAYERS Time-Programmable Current Source Pore Modulation in the z-Direction: Double Layer Pore Modulation in the z-Direction: Rugate Filter More Complicated Photonic Devices: Bragg Stacks, Microcavities, and Multi-Line Spectral Filters Lateral Pore Gradients (in the x-y Plane) Patterning in the x-y Plane Using Physical or Virtual Masks Other Patterning Methods FREESTANDING POROUS SILICON FILMS AND PARTICLES Freestanding Films of Porous Silicon-"Lift-offs" Micron-Scale Particles of Porous Silicon by Ultrasonication of Lift-off Films Core-Shell (Si/SiO2) Nanoparticles of Luminescent Porous Silicon by Ultrasonication CHARACTERIZATION OF POROUS SILICON Gravimetric Determination of Porosity and Thickness Electron Microscopy and Scanned Probe Imaging Methods Optical Reflectance Measurements Porosity, Pore Size, and Pore Size Distribution by Nitrogen Adsorption Analysis (BET, BJH, and BdB Methods) Measurement of Steady-State Photoluminescence Spectra Time-Resolved Photoluminescence Spectra Infrared Spectroscopy of Porous Silicon CHEMISTRY OF POROUS SILICON Oxide-Forming Reactions of Porous Silicon Biological Implications of the Aqueous Chemistry of Porous Silicon Formation of Silicon-Carbon Bonds Thermal Carbonization Reactions Conjugation of Biomolecules to Modified Porous Silicon Chemical Modification in Tandem with Etching Metallization Reactions of Porous Silicon APPENDIX A1. ETCH CELL ENGINEERING DIAGRAMS AND SCHEMATICS Standard or Small Etch Cell-Complete Standard Etch Cell Top Piece Small Etch Cell Top Piece Etch Cell Base (for Either Standard or Small Etch Cell) Large Etch Cell-Complete Large Etch Cell Top Piece Large Etch Cell Base APPENDIX A2. SAFETY PRECAUTIONS WHEN WORKING WITH HYDROFLUORIC ACID Hydrofluoric Acid Hazards First Aid Measures for HF Contact Note to Physician HF Antidote Gel APPENDIX A3. GAS DOSING CELL ENGINEERING DIAGRAMS AND SCHEMATICS Gas Dosing Cell Top Piece Gas Dosing Cell Middle Piece Gas Dosing Cell Bottom Piece
353 citations
TL;DR: In this article, secondary ion mass spectroscopy (SIMS) analysis is used for the first time to simultaneously monitor all the major impurities on a surface of a Si surface.
Abstract: Microporous and mesoporous Si layers contain a very large surface area that affects both their optical and electrical properties. Secondary ion mass spectroscopy (SIMS) analysis is used for the first time to simultaneously monitor all the major impurities on that surface. SIMS data on a microporous layer demonstrate that its chemical composition changes dramatically with time during ambient air exposure. Similar trends are observed for mesoporous layers. Extended storage in air at room temperature converts the hydride surface of freshly anodized layers to that of a contaminated native oxide. Characterization techniques need to take the metastability of the hydride surface into account since the structural, optical, and electrical properties of porous Si can consequently change with time upon exposure to ambient air. Low‐temperature photoluminescence and spectroscopic ellipsometry data on freshly anodized and ‘‘aged’’ microporous and mesoporous layers are chosen to illustrate typical changes in optical pro...
349 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