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 thickness of the Si1−xGex layers with a Ge content x in the range from about 20% to 27% were grown by Si•MBE at temperatures far below 550 °C (325−450 C).
Abstract: Ultrametastable silicon‐germanium (Si1−xGex) layers with a Ge content x in the range from about 20% to 27% were grown by Si‐MBE at temperatures far below 550 °C (325–450 °C). The thicknesses of the layers (up to 500 nm) exceed the equilibrium thickness by a factor of up to 50. We observe in the as‐grown samples without any annealing both the excitonic Si1−xGex band‐edge luminescence and a broad alloy luminescence of unknown origin. The two peaks have an energy difference of ≊144 meV and shift linearly with the Ge content. The alloy band luminescence disappears when strain relaxation sets on upon annealing at around 600 °C.
61 citations
TL;DR: A joint experimental and theoretical study has been carried out to rationalize the photoluminescence properties of SrTiO3 perovskite thin films synthesized through a soft chemical processing.
60 citations
TL;DR: In this paper, the thermal conductivity of porous silicon is measured as prepared and after oxidation using thermal wave propagation in the porous film, and three types of silicon are investigated: Nanoporous p-type silicon, nanoporous n-type and mesoporous P+ type silicon.
Abstract: The thermal conductivity of porous silicon is measured as prepared and after oxidation. The measurement method uses thermal wave propagation in the porous film. We investigate three types of porous silicon: Nanoporous p-type silicon, nanoporous n-type silicon and mesoporous p+-type silicon. The nanoporous material shows a thermal conductivity in the region of 1.2 W/mK to 1.8 W/mK as prepared and after oxidation. This value is close to silicon oxide. The mesoporous material shows a high thermal conductivity of 80 W/mK as prepared which drops to 2.7 W/mK after oxidation.
60 citations
TL;DR: In this paper, room temperature electroluminescence at 1.54 μm is demonstrated in erbium-implanted oxygen-doped silicon (27 at. % O), due to intra−4f transitions of the Er3+.
Abstract: Room‐temperature electroluminescence at 1.54 μm is demonstrated in erbium‐implanted oxygen‐doped silicon (27 at. % O), due to intra‐4f transitions of the Er3+. The luminescence is electrically stimulated by biasing metal‐(Si:O, Er)‐p+ silicon diodes. The 30‐nm‐thick Si:O, Er films are amorphous layers deposited onto silicon substrates by chemical‐vapor deposition of SiH4 and N2O, doped by ion implantation with Er to a concentration up to ≊1.5 at. %, and annealed in a rapid thermal annealing furnace. The most intense electroluminescence is obtained in samples annealed at 400 °C in reverse bias under breakdown conditions and it is attributed to impact excitation of erbium by hot carriers injected from the Si into the Si:O, Er layer. The electrical characteristics of the diode are studied in detail and related to the electroluminescence characteristics. A lower limit for the impact excitation cross section of ≊6×10−16 cm2 is obtained.
60 citations
TL;DR: In this article, a detailed study of nanostructure fabrication and optical characterization of sub-μm-period, one-dimensional, Si grating structures was performed using laser interferometric lithography with anisotropic wetchemical etching (KOH) and thermal oxidation.
Abstract: We report a detailed study of nanostructure fabrication and optical characterization of sub‐μm‐period, one‐dimensional, Si grating structures. Nanoscale wall width structures were fabricated by combining laser interferometric lithography with anisotropic wet‐chemical etching (KOH) and thermal oxidation. Structure wall widths were characterized by Raman scattering (RS) and scanning electron microscopy. Salient features of the RS measurements as a function of wall widths from ∼100 to 10 nm were: (a) large cross‐section enhancements, ∼100×, for linewidths ∼50 nm; (b) asymmetric line shapes with tails extending to smaller Raman shifts for linewidths ∼20 nm; and (c) splitting of the bulk Raman mode, again to lower Raman shifts, for linewidths ∼10 nm. For room temperature photoluminescence (PL) measurements, the grating structures were excited at 257 nm. PL measurements are reported for oxidized and unoxidized grating structures with peaks varying between 380 and 700 nm. PL was only observed for Si structures with dimensions less than about 10 nm. PL intensities and spectral line shapes varied significantly as a result of surface modification treatments such as high temperature anneal in a N2 atmosphere, immersion in boiling H2O, and long‐term exposure to ambient air. The measurements indicate a strong correlation of the visible PL with crystal size (∼5–10 nm); however, it remains unclear if the mechanism responsible is quantum confinement, passivation of the surface by Si:Hx complexes, or optically active surface states.
60 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