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.
Citations
More filters
TL;DR: In this paper, the authors reported optical luminescence in porous silicon and siloxene induced by soft X-rays with energies near the silicon K-edge (1,839 eV).
Abstract: FOLLOWING reports of intense optical luminescence from porous silicon1,2, the opportunity for engineering optoelectronic devices using this material3,4 has attracted considerable attention. At present, however, the question of the origin of the luminescence has not been fully resolved5. The quantum-confinement model6–8 suggests that a quantum size effect gives optical transitions, and hence luminescence, in the visible range—this idea gains support from the wavelength dependence of the luminescence on porosity. An alternative model9,10 attributes the luminescence to siloxene-like compounds11 formed on the silicon surface. A third model, which invokes hydrogenated amorphous silicon as a possible source12,13, seems to be contradicted by X-ray absorption fine structure (XAFS) studies14–16. Here we report optical luminescence in porous silicon and siloxene induced by soft X-rays with energies near the silicon K-edge (1,839 eV). Using the luminescence together with the total electron yield, we can obtain the XAFS spectra for the luminescent sites in both materials. Our results show that the luminescence from porous silicon does not derive from siloxene (either freshly prepared or annealed), and thus suggest that the quantum-confinement model seems to provide the only viable explanation.
175 citations
TL;DR: In this paper, the first direct observation of porous SiC formation from single-crystal SiC wafers has been reported, using TEM reveals pores of sizes 10-30 nm with interpore spacings ranging from roughly 5 to 150 nm.
Abstract: A process for forming porous SiC from single-crystal SiC wafers has been demonstrated. Porous SiC can be fabricated by anodizing n-type 6H-SiC in HF under UV illumination. TEM reveals pores of sizes 10-30 nm with interpore spacings ranging from roughly 5 to 150 nm. This is the first reported direct observation of porous SiC formation.
174 citations
TL;DR: In this article, the size and shape-dependent band gap energy of semiconductor compound nanomaterials (SCNs) is formulated and the model theory is based on the cohesive energy of the nanocrystals compared to the bulk ones.
173 citations
TL;DR: The application of nanomaterials in the field of optical sensors has become a new, growing area of interest in recent years as mentioned in this paper, where the authors mainly focus on the changes of spectral absorbance, photoluminescence (PL) and chemiluminecence (CL) phenomena induced by the interaction between nanommaterials and various analytes.
Abstract: The application of nanomaterials in the field of optical sensors has become a new, growing area of interest in recent years. We review chemical sensors that apply the optical principles of nanomaterials to the determination of chemical and biochemical analytes. We mainly focus on the changes of spectral absorbance, photoluminescence (PL) and chemiluminescence (CL) phenomena induced by the interaction between nanomaterials and various analytes.
173 citations
TL;DR: In this paper, the quenching of photoluminescence by the adsorbates has been quantified and correlation to the electrical conductivity of the porous silicon sample has been studied.
Abstract: Porous silicon (p type) has been exposed to several chemical vapors at various partial pressures. The quenching of the photoluminescence by the adsorbates has been quantified and correlation to the electrical conductivity of the porous silicon sample has been studied. Some gases, e.g., water and benzene, have a small effect on the photoluminescence and on the conductivity, while others, e.g., methanol, reduce the photoluminescence by a factor of 2 and increase the conductivity by four orders of magnitude. This is accompanied with a qualitative change in the current‐voltage characteristics. These changes have been found to be reversible and the temporal behavior of the system has been investigated.
172 citations
References
More filters
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