Showing papers on "Silicon published in 1992"
TL;DR: In this article, various models describing porous silicon formation are reviewed and the known electrochemical and morphological properties are discussed with the intention of unifying the different models into a comprehensive explanation for the formation of a porous structure in silicon.
Abstract: Recent reports describing photoluminescence in porous silicon have heightened the level of interest in it as a unique electronic material, and have created a need for a more complete understanding of the mechanism of porous silicon formation. The various models describing porous silicon formation are reviewed and the known electrochemical and morphological properties are discussed with the intention of unifying the different models into a comprehensive explanation for the formation of a porous structure in silicon. Because the specific surface dissolution chemistry is critical for a complete understanding of pore formation, some of the more prominent dissolution reactions are also reviewed and their relative importance to pore generation and morphology is discussed. Some aspects of the recently reported quantum effects are also reviewed. Because the mechanism of porous silicon formation involves a wide range of interdisciplinary fields, a considerable number of analogies and examples to related phenomena ...
1,000 citations
TL;DR: In this paper, the authors compared the luminescence and vibrational properties of anodically oxidized (porous) silicon and of chemically synthesized siloxene (Si 6 O 3 H 6 ) and its derivates.
738 citations
TL;DR: In this paper, photoluminescent porous Si (PS) layers exhibit visible electroluminescence (EL) when the forward current density reaches a certain value, stable visible (orange) light is uniformly emitted through a semitransparent electrode.
Abstract: It is demonstrated that photoluminescent porous Si (PS) layers exhibit definitely visible electroluminescence (EL). The PS layers were formed by anodization of single‐crystal nondegenerate p‐type Si wafers in an HF solution. The experimental EL cells are of the form semitransparent metal/PS layer/p‐type Si/Al electrode. These cells show a rectifying junction behavior. When the forward current density reaches a certain value, stable visible (orange) light is uniformly emitted through a semitransparent electrode. A possible explanation of this is the radiative transition due to electron and hole injection into quantized states in PS.
620 citations
TL;DR: In this article, the tetramethyl ammonium hydroxide (TMAH, (CH3)4NOH) was used for silicon anisotropic etching solutions with various concentrations from 5 to 40 wt.% and temperatures from 60 to 90 °C.
Abstract: Detailed characteristics of tetramethyl ammonium hydroxide (TMAH, (CH3)4NOH) as silicon anisotropic etching solutions with various concentrations from 5 to 40 wt.% and temperatures from 60 to 90 °C have been studied. The etch rates of (100) and (110) crystal planes decrease with increasing concentration. The etched (100) planes are covered by pyramidal hillocks below 15 wt.%, but very smooth surfaces are obtained above 22 wt.%. Etch rates of 1.0 μ/min for the (100) plane and 1.4 μ/min for the (110) plane at 90 °C are obtained using a 22 wt.% solution. The etch-rate ratio of (111)/(100) varies from 0.02 to 0.08. The etch rate of thermally oxidized SiO2 is almost four orders of magnitude lower than that for (100) and (110) planes. The etch rates of aluminium are reduced by dissolving silicon in TMAH solution. Etch-stop techniques using a heavily boron-doped layer or p—n junction prove to be applicable to TMAH solutions.
448 citations
TL;DR: A model is proposed to help explain bias-enhanced nucleation on silicon, in hopes that this will improve the understanding of diamond nucleation, in general, and eventually result in the nucleation and growth of better-quality diamond films.
Abstract: An in-depth study has been performed of the nucleation of diamond on silicon by bias-enhanced microwave plasma chemical vapor deposition. Substrates were pretreated by negative biasing in a 2% methane-hydrogen plasma. The bias pretreatment enhanced the nucleation density on unscratched silicon wafers up to ${10}^{11}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ as compared with ${10}^{7}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ on scratched wafers. In vacuo surface analysis including x-ray photoelecton spectroscopy (XPS), Auger electron spectroscopy, and combined XPS and electron-energy-loss spectroscopy were used to study systematically both the initial-nucleation and growth processes. High-resolution cross-sectional transmission electron microscopy (TEM) was used to study the physical and structural characteristics of the diamond-silicon interface as well as to complement and enhance the in vacuo surface-analytical results. Raman spectroscopy confirmed that diamond was actually nucleating during the bias pretreatment. Scanning electron microscopy has shown that once the bias is turned off, and conventional growth is conducted, diamond grows on the existing nuclei and no continued nucleation occurs. If the bias is left on throughout the entire deposition, the resulting film will be of much poorer quality than if the bias had been turned off and conventional growth allowed to begin. Intermittent surface analysis showed that a complete silicon carbide layer developed before diamond could be detected. High-resolution cross-sectional TEM confirmed that the interfacial layer was amorphous and varied in thickness from 10 to 100 \AA{}. A small amount of amorphous carbon is detected on the surface of the silicon carbide and it is believed to play a major role in the nucleation sequence. A model is proposed to help explain bias-enhanced nucleation on silicon, in hopes that this will improve the understanding of diamond nucleation, in general, and eventually result in the nucleation and growth of better-quality diamond films.
448 citations
TL;DR: In this article, the experimentally observed dependence of effective surface recombination velocity Seff at the Si-SiO2 interface on light-induced minority carrier excess concentration is compared with theoretical predictions of an extended Shockley-Read-Hall (SRH) formalism.
Abstract: The experimentally observed dependence of effective surface recombination velocity Seff at the Si‐SiO2 interface on light‐induced minority carrier excess concentration is compared with theoretical predictions of an ‘‘extended Shockley–Read–Hall (SRH) formalism.’’ The calculations of SRH‐recombination rates at the Si‐SiO2 interface are based on the theory of a surface space charge layer under nonequilibrium conditions and take into account the impact of illumination level, gate metal work function, fixed oxide charge density, and the energy dependence of capture cross sections σn, σp and interface state density Dit. Applying this theory to p‐type silicon surfaces covered by high quality thermal oxides, the experimentally observed strong increase of Seff with decreasing minority carrier excess concentration could quantitatively be attributed to the combined effect of the σn/σp ratio of about 1000 at midgap and the presence of a positive fixed oxide charge density Qf of about 1×1011 charges/cm2. Due to the f...
429 citations
TL;DR: In this paper, the stability of the luminescence from porous Si in the presence of a variety of ambient gases (e.g., N2, H2, forming gas, and O2) was studied.
Abstract: We have studied the stability of the luminescence from porous Si in the presence of a variety of ambient gases (e.g., N2, H2, forming gas, and O2). Although the optical properties are fairly stable under most conditions, illumination in the presence of O2 causes a substantial decrease in luminescence efficiency. Infrared measurements show that the surfaces of degraded samples are oxidized. The luminescence lifetime of the degraded material is found to be substantially reduced, and the density of Si dangling bonds increases by more than two orders of magnitude, which suggests that oxidation of the surface introduces nonradiative recombination channels. These observations indicate that the electronic properties at the surface of the porous Si play a key role in obtaining efficient luminescence from this material.
420 citations
TL;DR: In this article, the electronic structure of spherical silicon crystallites containing up to 2058 Si atoms was calculated and a variation of the optical band gap with respect to the size of the crystallites was predicted in very good agreement with available experimental results.
Abstract: We have calculated the electronic structure of spherical silicon crystallites containing up to 2058 Si atoms. We predict a variation of the optical band gap with respect to the size of the crystallites in very good agreement with available experimental results. We also calculate the electron‐hole recombination time which is of the order of 10−4–10−6 s for crystallites with diameters of 2.0–3.0 nm. We conclude that small silicon crystallites can have interesting optical properties in the visible range. These results are applied to porous silicon for which we confirm that a possible origin of the luminescence is the quantum confinement.
419 citations
TL;DR: High-porosity porous silicon, after electrochemical oxidation, is a stable and highly reproducible luminescent material with a luminescence quantum efficiency as high as 3% at room temperature and this tunneling model is used to explain successfully the increase in quantum efficiency with the increase of the level of oxidation.
Abstract: High-porosity porous silicon, after electrochemical oxidation, is a stable and highly reproducible luminescent material with a luminescence quantum efficiency as high as 3% at room temperature. Luminescence decay rates as long as several hundreds of microseconds show that radiative and nonradiative processes both have low efficiencies even at room temperature. This shows that confinement of carriers inside nanometer-sized crystallites does not have a noticeable effect on indirect-band-gap selection rules but restricts strongly the different processes for nonradiative deexcitation. An analysis of the dependence of the nonradiative-decay rates on carrier confinement in terms of the tunneling of carriers through silicon oxide barriers surrounding the confined zone accounts well for our experimental results with an average barrier thickness of 5 nm. This tunneling model is also used to explain successfully the increase in quantum efficiency with the increase of the level of oxidation.
405 citations
TL;DR: The manufacturing techniques used to create the electrode arrays, focusing on the dielectric isolation technique, are described, and the electrical and mechanical characteristics of these arrays are discussed.
Abstract: A new manufacturing technique has been developed for creating silicon-based, penetrating electrode arrays intended for implantation into cerebral cortex. The arrays consist of a 4.2 mm x 4.2 mm glass/silicon composite base, from which project 100 silicon needle-type electrodes in a 10 x 10 array. Each needle is approximately 1,500 microns long, 80 microns in diameter at the base, and tapers to a sharp point at the metalized tip. The technique used to manufacture these arrays differs from our previous method in that a glass dielectric, rather than a p-n-p junction, provides electrical isolation between the individual electrodes in the array. The new electrode arrays exhibit superior electrical properties to those described previously. We have measured interelectrode impedances of at least 10(13) omega, and interelectrode capacitances of approximately 50 fF for the new arrays. In this paper, we describe the manufacturing techniques used to create the arrays, focusing on the dielectric isolation technique, and discuss the electrical and mechanical characteristics of these arrays.
375 citations
TL;DR: Comparison with effective-mass theory shows that the latter is valid for wires wider than 23 A, and first-principles pseudopotential calculations for H-terminated Si wires with thicknesses from 12 to 23 A are performed.
Abstract: We have performed first-principles pseudopotential calculations for H-terminated Si wires with thicknesses from 12 to 23 \AA{}, calculating the band gaps and optical matrix elements. Comparison with effective-mass theory shows that the latter is valid for wires wider than 23 \AA{}. We have used our data to analyze the luminescent properties of highly porous Si fabricated by electrochemical etching of Si wafers in HF-based solutions.
TL;DR: In this article, GaN films have been epitaxially grown onto (001) Si by electron cyclotron resonance microwave-plasma assisted molecular beam epitaxy, using a two-step growth process, in which a GaN buffer is grown at relatively low temperatures and the rest of the film is growing at higher temperatures.
Abstract: GaN films have been epitaxially grown onto (001) Si by electron cyclotron resonance microwave‐plasma‐assisted molecular‐beam epitaxy, using a two‐step growth process, in which a GaN buffer is grown at relatively low temperatures and the rest of the film is grown at higher temperatures. This method of film growth was shown to lead to good single‐crystalline β‐GaN and to promote lateral growth resulting in smooth surface morphology. The full width at half‐maximum of the x‐ray rocking curve in the best case was found to be 60 min. Optical‐absorption measurements indicate that the band gap of β‐GaN is 3.2 eV and the index of the refraction below the absorption edge is 2.5. Conductivity measurements indicate that the films may have a carrier concentration below 1017 cm−3.
TL;DR: In this article, the authors reported the direct transformation of a metallorganic precursor into non-oxide silicon-based ceramics with relative densities of up to 93% without the addition of sintering aids.
Abstract: THE conventional preparation of advanced ceramic parts based on silicon carbide or nitride involves pressureless sintering, hot pressing or hot isostatic pressing of appropriate ceramic starting powders1. Owing to the covalent nature of the Si–C and Si–N bonds and hence the low diffusion coefficients in SiC and Si3N4, high sintering temperatures and the addition of sintering aids are normally used to enhance densification. During densification, the sintering additives form second phases located at grain boundaries, which commonly impair the mechanical and physical properties of the material, especially at higher temperatures. New processing routes that overcome these problems are therefore desirable. Here we report the direct transformation of a metallorganic precursor into non-oxide silicon-based ceramics with relative densities of up to 93%. This process can be used to make ceramic components and matrix composites at unusually low temperatures (1,000 °C) and without the addition of sintering aids.
TL;DR: Porous silicon that strongly emits in the visible was analyzed using Raman scattering and it was shown that the local structure of porous silicon is more like a sphere than a rod and has a characteristic diameter of 2.5-3.0 nm as mentioned in this paper.
Abstract: Porous silicon that strongly emits in the visible was analyzed using Raman scattering. The spectrum peaks near 508 cm−1, has a width of ∼40 cm−1, and is very asymmetric. Using a model of phonon confinement, this suggests that the local structure of porous silicon is more like a sphere than a rod and has a characteristic diameter of 2.5–3.0 nm. Polarization Raman measurements suggest that the structure does not consist of a series of parallel columns.
TL;DR: In this article, a dielectric function model yielding a Gaussian shape of the absorption lines and satisfying Kramers-Kronig relations was suggested for modeling of infrared spectra.
Abstract: For the modeling of infrared spectra it is a common approach to use a dielectric function that treats the vibrational modes as damped harmonic oscillators. This model was found to be rather crude for some applications to amorphous solids. A dielectric function model yielding a Gaussian shape of the absorption lines and satisfying Kramers–Kronig relations is suggested. The model function is constructed by a convolution of a Gaussian function with the dielectric function of the damped harmonic oscillator model. An analytical solution of this integral is given. It is demonstrated that this model describes the spectra of thermally grown ultrathin (1.3 nm) silicon oxide films, plasma‐deposited silicon films, plasma‐deposited silicon nitride films, and amorphous aluminum oxide films very well. The physical motivation of the dielectric function model suggested is the randomness of the vibrational frequencies in an amorphous structure.
IBM1
TL;DR: It is shown that first-principles electronic structure calculations of silicon wires with diameters up to 1.5 nm support the idea that quantum confinement and surface effects are responsible for the luminescence in porous silicon.
Abstract: We show that first-principles electronic structure calculations of silicon wires with diameters up to \ensuremath{\sim}1.5 nm support the idea that quantum confinement and surface effects are responsible for the luminescence in porous silicon. Instead of the indirect gap of crystalline bulk silicon, the band structure of these wires exhibits a direct gap at k=0. The imaginary part of the dielectric function, polarized in the direction of the wire, shows a peak in the visible range. The dependence of this feature on wire size is analyzed and correlated to experimental luminescence spectra.
TL;DR: Extremely well-resolved Si 2p core-level spectra have been obtained and the split of ∼0.55 eV between the two dimer-atom components points to a substantial charge transfer within the dimers.
Abstract: Extremely well-resolved Si 2p core-level spectra have been obtained from the clean Si(001) surface. Spectra from the cold c(4×2) and the RT 2×1 surfaces are very similar, implying that the local structure of the two reconstructions is the same. Shifted components originating from both up and down atoms of asymmetric dimers, as well as second-layer atoms, are identified. The split of ∼0.55 eV between the two dimer-atom components points to a substantial charge transfer within the dimers. We find no support for the recently proposed crystal-field splitting of the surface components
TL;DR: In this article, the effects of silicon surface microroughness on electrical properties of thin-oxide films, such as breakdown electric field intensity (E/sub BD/) and time-dependent dielectric breakdown (Q/subBD/), have been studied, where the MICROUGE of silicon and silicon dioxide surfaces are evaluated by the scanning tunneling microscope (STM) and the atomic force microscope (AFM), respectively.
Abstract: The effects of silicon surface microroughness on electrical properties of thin-oxide films, such as breakdown electric field intensity (E/sub BD/) and time-dependent dielectric breakdown (Q/sub BD/), have been studied, where the microroughnesses of silicon and silicon dioxide surfaces are evaluated by the scanning tunneling microscope (STM) and the atomic force microscope (AFM), respectively. An increase of surface microroughness has been confirmed to severely degrade the E/sub BD/ and Q/sub BD/ characteristics of thin-oxide films with thicknesses of 8-10 nm and to simultaneously decrease channel electron mobility. An increase of surface microroughness has been demonstrated to originate mainly from wet chemical cleaning processing based on the RCA cleaning concept, particularly the ammonium-hydrogen-peroxide cleaning step. In order to keep the surface microroughness at an initial level, the content ratio of NH/sub 4/OH/H/sub 2/O/sub 2//H/sub 2/O solution has been set at 0.05:1:5 and the room-temperature DI water rinsing has been introduced right after the NH/sub 4/OH/H/sub 2/O/sub 2//H/sub 2/O cleaning step in conventional RCA cleaning procedure. >
TL;DR: In this paper, the results on the thermo-optical induced modulation in a silicon etalon at 1.5 µm were reported. But the results were limited to the case where the etalon was used to measure the temperature of the silicon at this wavelength.
Abstract: Experimental results on thermo-optical induced modulation in a silicon etalon at 1.5/m are reported. The measurements have also allowed an accurate determination of the thermooptic effect in silicon at this wavelength.
IBM1
TL;DR: A liquid-solution-phase technique for preparing submicrometer-sized silicon single crystals is presented, based on the reduction of SiCl4 and RSiCl3 by sodium metal in a nonpolar organic solvent at high temperatures and high pressures.
Abstract: A liquid-solution-phase technique for preparing submicrometer-sized silicon single crystals is presented. The synthesis is based on the reduction of SiCl(4) and RSiCl(3) (R = H, octyl) by sodium metal in a nonpolar organic solvent at high temperatures (385 degrees C) and high pressures (> 100 atmospheres). For R = H, the synthesis produces hexagonal-shaped silicon single crystals ranging from 5 to 3000 nanometers in size. For R = octyl, the synthesis also produces hexagonal-shaped silicon single crystals; however, the size range is controlled to 5.5 +/- 2.5 nanometers.
TL;DR: In this paper, the authors reported epitaxial growth of TiN films having low resistivity on (100) silicon substrates using pulsed laser deposition method and showed 10% to 20% channeling yield.
Abstract: We report epitaxial growth of TiN films having low resistivity on (100) silicon substrates using pulsed laser deposition method. The TiN films were characterized using x‐ray diffraction, Rutherford backscattering, four‐point‐probe ac resistivity, high resolution transmission electron microscopy and scanning electron microscopy techniques and epitaxial relationship was found to be 〈100〉 TiN ∥ 〈100〉 Si. TiN films showed 10%–20% channeling yield. In the plane, four unit cells of TiN match with three unit cells of silicon with less than 4.0% misfit. This domain matching epitaxy provides a new mechanism of epitaxial growth in systems with large lattice misfits. Four‐point‐probe measurements show characteristic metallic behavior of these films as a function of temperature with a typical resistivity of about 15 μΩ cm at room temperature. Implications of low‐resistivity epitaxial TiN in silicon device fabrication are discussed.
TL;DR: In this article, the luminescence properties of 3 μm thick, strongly emitting, and highly porous silicon films were studied using a combination of photoluminescence, transmission electron microscopy, and Fourier transform infrared spectroscopy.
Abstract: The luminescence properties of 3 μm thick, strongly emitting, and highly porous silicon films were studied using a combination of photoluminescence, transmission electron microscopy, and Fourier transform infrared spectroscopy. Transmission electron micrographs indicate that these samples have structures of predominantly 6–7 nm size clusters (instead of the postulated columns). In the as‐prepared films, there is a significant concentration of Si—H bonds which is gradually replaced by Si—O bonds during prolonged aging in air. Upon optical excitation these films exhibit strong visible emission peaking at ≊690 nm. The excitation edge is shown to be emission wavelength dependent, revealing the inhomogeneous nature of both the initially photoexcited and luminescing species. The photoluminescence decay profiles observed are highly nonexponential and decrease with increasing emission energy. The 1/e times observed typically range from 1 to 50 μs. The correlation of the spectral and structural information suggest...
TL;DR: In this article, the silicide-mediated phase transformation of amorphous to crystalline silicon was observed in situ in the transmission electron microscope, and a diffusion-controlled mechanism for the enhanced crystallization rate was determined.
Abstract: The silicide‐mediated phase transformation of amorphous to crystalline silicon was observed in situ in the transmission electron microscope. Crystallization of nickel‐implanted amorphous silicon occurred at ∼500 °C. Nickel disilicide precipitates were observed to migrate through an amorphous Si film leaving a trail of crystalline Si. Growth occurred parallel to 〈111〉 directions. High resolution electron microscopy revealed an epitaxial NiSi2/Si(111) interface which was Type A. A diffusion‐controlled mechanism for the enhanced crystallization rate was determined.
TL;DR: In this paper, the correlation energy of crystalline silicon is determined by means of increments obtained in ab initio calculations for localized SiSi bond orbitals and for pairs and triples of such bonds.
TL;DR: In this article, an analytical review of the last five or six years of research and development in SiC is presented, which outlines the major achievements in single crystal growth and device technology.
Abstract: The present paper is an analytical review of the last five or six years of research and development in SiC. It outlines the major achievements in single crystal growth and device technology. Electrical performance of SiC devices designed during these years and some new trends in SiC electronics are also discussed. During the 1980s the studies on sublimation and liquid-phase epitaxial growth of SiC single crystal were continued successfully. At that time, such methods as chemical vapour deposition, thermal oxidation, 'dry' plasma etching and ion implantation which yielded good results with silicon, came into use. As a result of the technological progress, discrete devices appeared, which incorporated the potential advantages of SiC as a wide bandgap material. Among these were high temperature (500-600 degrees C) rectifier diodes and field-effect transistors, high efficiency light-emitting diodes for the short-wave region of the visible spectrum, and detectors of ultraviolet radiation. It should be stressed that the devices were of commercial quality and could be applied in various fields (control systems of automobile engines, aerospace apparatus, geophysical equipment, colour displays in information systems, etc.). The developments in technology and the promising results of research on electrical performance of the devices already available give hope that in the near future SiC may become the basic material for power microwave devices, and for thermo- and radiation-resistant integrated circuits. This process can be stimulated by further perfection of single-crystal substrates of large area, by development of stable high temperature ohmic contacts, micro- and heterostructures.
TL;DR: Transmission electron microscopy analyses show that the Si particles have irregular shapes, with diameters ranging from many micrometers to nanometers, and can be made by the addition of polystyrene to a toluene suspension of the Si nanoparticles and casting of the resulting solution onto a glass slide.
Abstract: A procedure for generating colloidal suspensions of Si that exhibit luminescence, attributed to quantum confinement effects, is described. Samples of n- or p-type Si that have been electrochemically etched to form porous Si can be ultrasonically dispersed into methylene chloride, acetonitrile, methanol, toluene, or water solvents, forming a suspension of fine Si particles that luminesce. Transmission electron microscopy analyses show that the Si particles have irregular shapes, with diameters ranging from many micrometers to nanometers. Luminescent, composite polystyrene/Si films can be made by the addition of polystyrene to a toluene suspension of the Si nanoparticles and casting of the resulting solution onto a glass slide.
TL;DR: In this paper, a correlation of Raman and photoluminescence spectra was found to indicate that the observed luminescence originates from extremely small microstructures.
Abstract: The discovery of luminescence in electrochemically etched porous silicon is an extremely important scientific breakthrough with enormous technological implications. It opens the door for silicon, the most important microelectronic material, as a possible material for optoelectronics applications. Our result, a correlation of Raman and photoluminescence spectra, shows that the observed luminescence is originated from extremely small microstructures. As the luminescent peak increases in photon energy, the Raman feature shifts to lower energy, remaining sharp, and eventually splits, developing into TO and LO modes. No peak at 480 cm−1 is observed, which indicates no substantial contribution from an amorphous region. These data provide strong evidence of the role of microstructures in porous silicon.