Showing papers on "Doping published in 1994"

The Role of Metal Ion Dopants in Quantum-Sized TiO2: Correlation between Photoreactivity and Charge Carrier Recombination Dynamics

Abstract: A systematic study of metal ion doping in quantum (Q)-sized (2-4 nm) TiO_2 colloids is performed by measuring their photoreactivities and the transient charge carrier recombination dynamics. The presence of metal ion dopants in the TiO_2 crystalline matrix significantly influences photoreactivity, charge carrier recombination rates, and interfacial electron-transfer rates. The photoreactivities of 21 metal ion-doped colloids are quantified in terms of both the conduction band electron reduction of an electron acceptor (CCl_4 dechlorination) and the valence band hole oxidation of an electron donor (CHCl_3 degradation). Doping with Fe^(3+), Mo^(5+), Ru^(3+), Os^(3+), Re^(5+), V^(4+), and Rh^(3+) at 0.1-0.5 at.% significantly increases the photoreactivity for both oxidation and reduction while Co^(3+) and Al^(3+) doping decreases the photoreactivity. The transient absorption signals upon laser flash photolysis (λ_(ex) = 355 nm) at λ = 600 nm are extended up to 50 ms for Fe^(3+)-, V^(4+)-, Mo^(5+)-, and Ru^(3+)-doped TiO_2 while the undoped Q-sized TiO_2 shows a complete "blue electron" signal decay within 200 μs. Co^(3+)- and Al^(3+)-doped TiO_2 are characterized by rapid signal decays with a complete loss of absorption signals within 5 μs. The quantum yields obtained during CW photolyses are quantitatively correlated with the measured transient absorption signals of the charge carriers. Photoreactivities are shown to increase with the relative concentration of trapped charge carriers. The photoreactivity of doped TiO_2 appears to be a complex function of the dopant concentration, the energy level of dopants within the TiO_2 lattice, their d electronic configuration, the distribution of dopants, the electron donor concentration, and the light intensity.

Stability and Band Gap Constancy of Boron Nitride Nanotubes

Abstract: Extensive LDA and quasi-particle calculations have been performed on boron nitride (BN) single-wall and multi-wall nanotubes. Strain energies are found to be smaller for BN nanotubes than for carbon nanotubes of the same radius, owing to a buckling effect which stabilizes the BN tubular structure. For tubes larger than 9.5 A in diameter, the lowest conduction band is predicted to be free-electron-like with electronic charge density localized inside the tube. For these tubes, this band is at constant energy above the top of the valence band. Consequently, contrarily to carbon nanotubes, single- and multi-wall BN nanotubes are constant-band-gap materials, independent of their radius and helicity. In addition, we expect them to exhibit remarkable properties under n-type doping.

VLSI fabrication principles : silicon and gallium arsenide

Abstract: Material Properties. Phase Diagrams and Solid Solubility. Crystal Growth and Doping. Diffusion. Epitaxy. Ion Implantation. Native Films. Deposited Films. Etching and Cleaning. Lithographic Processes. Device and Circuit Fabrication. Appendix. Index.

Photoluminescence of AlxGa1−xAs alloys

Abstract: A thorough discussion of the various features of the photoluminescence spectra of undoped, p‐doped and n‐doped AlxGa1−xAs (0≤x≤1) alloys is given. This review covers spectral features in the energy region ranging from the energy band gap down to ≂0.8 eV, doping densities from isolated impurities to strongly interacting impurities (heavy‐doping effects) and lattice temperatures from 2 to 300 K. The relevance of photoluminescence as a simple but very powerful characterization technique is stressed also in comparison with other experimental methods. The most recent determinations of the Al concentration dependence of some physical properties of the alloy (energy gaps, carrier effective masses, dielectric constants, phonon energies, donor and acceptor binding energies, etc.) are given. The main physical mechanisms of the radiative recombination process in semiconductors are summarized with particular emphasis on the experimental data available for AlxGa1−xAs. The effects of the nature of the band gap (direct ...

Site‐competition epitaxy for superior silicon carbide electronics

Abstract: We present and discuss a novel dopant control technique for compound semiconductors, called site‐competition epitaxy, which enables a much wider range of reproducible doping control and affords much higher and lower epilayer doping concentrations than was previously possible. Site‐competition epitaxy is presented for the chemical vapor deposition of 6H‐SiC epilayers on commercially available (0001)SiC silicon‐face substrates. Results from utilizing site‐competition epitaxy include the production of degenerately doped SiC epilayers for ohmic‐as‐deposited (i.e., unannealed) metal contacts as well as very low doped epilayers for electronic devices exhibiting SiC record‐breaking reverse voltages of 300 and 2000 V for 3C‐ and 6H‐SiC p‐n junction diodes, respectively.

Optical and electrical properties of radio frequency sputtered tin oxide films doped with oxygen vacancies, F, Sb, or Mo

Abstract: Tin oxide films doped with oxygen vacancies, F, Sb, or Mo were made by reactive rf magnetron sputtering of Sn, Sn‐Sb, or Sn‐Mo in Ar+O2(+CF4) onto glass heated to a temperature up to 530 °C. Electrical dc resistivity, mobility, free‐electron density, spectral optical properties, and microstructure were investigated as a function of sputtering parameters. Optimized deposition parameters gave SnOx:(Sb,F) films with high luminous transmittance, low luminous absorptance, high infrared reflectance, and dc resistivity down to 9.1×10−4 Ω cm. Refractive index n and extinction coefficient k were evaluated from spectrophotometric transmittance. In the luminous range, the films had 1.90

Physical Properties of Mixed Conductor Solid Oxide Fuel Cell Anodes of Doped CeO2

Abstract: Samples of CeO2 doped with oxides such as CaO and Gd203 were prepared. Their conductivities and expansions on reduction were measured at 1000~ and the thermal expansion coefficients in the range 50 to 1000~ were determined. The ionic and electronic conductivity were derived from curves of total conductivity vs. oxygen partial pressure. For both types of conductivity a dependence on dopant valency was observed. The electronic conductivity was independent of dopant radius in contrast to the ionic which was highly dependent. These measured physical properties are compared with the ideal requirements for solid oxide fuel cell anodes. Not all requirements are fulfilled. Measures to compensate for this are discussed.

P-type conduction in mg-doped gan and al0.08ga0.92n grown by metalorganic vapor phase epitaxy

Abstract: Temperature dependences of the hole concentration and Hall mobility in Mg‐doped GaN and Al0.08Ga0.92N grown by metalorganic vapor phase epitaxy were measured by the van der Pauw method over a wide temperature range from 100 to 500 K. Assuming that the effective mass of holes in Al0.08Ga0.92N is equal to that of GaN, the activation energy of the Mg shallow acceptor in Al0.08Ga0.92N is estimated to be about 35 meV deeper than that in GaN.

Grain Boundary Defect Chemistry of Acceptor‐Doped Titanates: Space Charge Layer Width

Abstract: The grain boundary space charge depletion layers in acceptor-doped SrTiO3 and BaTiO3 ceramics were investigated by impedance spectroscopy in the time and frequency domain. Based on the layer width and its dependence on the acceptor concentration, the temperature, and the oxygen partial pressure during annealing, a suggestion for a refined Schottky model is proposed. The local distribution of the donor-type grain boundary states causing the depletion layer and the resulting band bending are discussed.

Process for fabricating thin film transistor

Abstract: After a pattern is transferred on silicon film crystallized by annealing, the silicon film is annealed by radiation of intense rays for a short time. Especially, in the crystallizing process by annealing, an element which promotes crystallization such as nickel is doped therein. The area not crystallized by annealing is also crystallized by radiation of intense rays and a condensed silicon film is formed. After a metal element which promotes crystallization is doped, annealing by light for a short time is performed by radiating intense rays onto the silicon film crystallized by annealing in an atmosphere containing halide. After the surface of the silicon film is oxidized by heating or by radiating intense rays in a halogenated atmosphere and an oxide film is formed on the silicon film, the oxide film is then etched. As a result, nickel in the silicon film is removed.

Optical-properties of pecvd erbium-doped silicon-rich silica - evidence for energy-transfer between silicon microclusters and erbium ions (vol 6, pg l 319, 1994)

Abstract: We report the fabrication by PECVD of silicon-rich erbium-doped silica films that exhibit both 1535 nm fluorescence and visible photoluminescence. Fluorescence spectra are presented along with absorption spectra that display a strong band edge in the blue, which we ascribe to the presence of Si microclusters. We are unable to observe characteristic Er3+ absorption bands and propose that excitation of the rare earth is via an energy transfer process from Si microclusters.

Optical-properties of pecvd erbium-doped silicon-rich silica - evidence for energy-transfer between silicon microclusters and erbium ions

Abstract: We report the fabrication by PECVD of silicon-rich erbium-doped silica films that exhibit both 1535 nm fluorescence and visible photoluminescence. Fluorescence spectra are presented along with absorption spectra that display a strong band edge in the blue, which we ascribe to the presence of Si microclusters. We are unable to observe characteristic Er3+ absorption bands and propose that excitation of the rare earth is via an energy transfer process from Si microclusters.

Semiconductor electrical heater and method for making same

Abstract: A method is disclosed for mechanically and electrically bonding metallic materials and semiconductor materials. The method according to the invention may be used, for example, in forming a semiconductor electrical heater, particularly for use in electrical smoking articles. A metallic element, such as a copper alloy power supply tab, is laser welded to a semiconductor element, such as a doped silicon resistive heater element. A laser beam is directed through a hole in the copper alloy tab to melt some silicon material, which flows into the hole in the copper tab, reacts and intermixes with the copper and solidifies to form a slug containing copper silicide. A protective material such as nickel may be applied to protect the copper silicide from oxidation if desired. An ohmic, low resistance contact and high strength bond is provided between the parts.

Monolithic array of light emitting diodes for the generation of light at multiple wavelengths and its use for multicolor display applications

Abstract: Disclosed are monolithic multicolor arrays of light emitting diodes and their use for multicolor display applications. A multicolor LED array comprises a conductive substrate (35), a conductive semiconductor layer (36), a compensated semiconductor layer on top of the conductive semiconductor layer (36), and contacts (37; 38.x, x=1, 2, ...) for biasing individual LEDs. The compensated semiconductor layer serves as active layer of the LEDs for the generation of light. The multicolor capability of the active layer is achieved by using impurity related electronic transitions as radiative recombination processes, the energy of these transitions being dependent on the doping conditions, and by introducing a lateral variation of the doping conditions of the active layer. This lateral variation (different doping conditions are denoted by different symbols Di, i=1, 2, ...) is tailored such that a lateral variation of the color of the light generated in the active layer occurs due to the injection of carriers into the active layer, thus leading to LEDs with different emission wavelengths. The use of wide-bandgap semiconductors such as (Ga1-xAlx)1-yInyN for the active layer allows for fabricating monolithic multicolor LED arrays capable of generating different emission lines, all together spanning the entire spectrum between near infrared and ultraviolet.

Encapsulated quantum sized doped semiconductor particles and method of manufacturing same

Abstract: Doped encapsulated semiconductor nanoparticles of a size (<100 Å) which exhibit quantum effects. The nanoparticles are precipitated and coated with a surfactant by precipitation in an organometallic reaction. The luminescence of the particles may be increased by a further UV curing step.

Method of doping metal layers for electromigration resistance

Abstract: A method of doping metal layers on integrated circuits to provide electromigration resistance and integrated circuits having metal alloy interconnects characterized by being resistant to electromigration are provided. The process consists of the steps of (1) depositing a film of a pure first conductive metal upon a semiconductor, (2) patterning and etching the deposited film, (3) subjecting the patterned conductive metal film to metallo-organic chemical vapor deposition in order to deposit upon the first deposited metal and not upon any semiconductive areas present in the patterned conductive metal film a doping amount of a second conductive metal different from the first metal, and (4) heating at a temperature sufficient to uniformly diffuse the second metal through the bulk of the patterned first conductive metal film.

p‐type gallium nitride by reactive ion‐beam molecular beam epitaxy with ion implantation, diffusion, or coevaporation of Mg

Abstract: Gallium nitride is one of the most promising materials for ultraviolet and blue light‐emitting diodes and lasers. The principal technical problem that limits device applications has been achieving controllable p‐type doping. Molecular beam epitaxy assisted by a nitrogen ion beam produced p‐type GaN when doped via ion implantation, diffusion, or coevaporation of Mg. Nearly intrinsic p‐type material was also produced without intentional doping, exhibiting hole carrier concentrations of 5×1011 cm−3 and hole mobilities of over 400 cm2/V/s at 250 K. This value for the hole mobility is an order of magnitude greater than previously reported.

Electrochemical Er doping of porous silicon and its room‐temperature luminescence at ∼1.54 μm

Abstract: We present a new electro‐chemical method for incorporating high concentration Er ions deep into porous silicon layers and its intense photoluminescence at ∼1.54 μm at room temperature. Porous silicon layers prepared by anodic etching of p‐type silicon substrates in HF/H2O are immersed in ErCl3/ethanol solution. Then the negative bias relative to a counter platinum electrode is applied to the samples. Er3+ ions are drawn into fine pores of the porous silicon layers by the electric field. After thermal annealing at ∼1300 °C in an O2/Ar atmosphere, the samples show sharp and intense Er3+‐related photoluminescence at ∼1.54 μm at room temperature upon excitation with an Ar ion laser.

Method for etching boron nitride

Abstract: The subject invention provides a method of enhancing the etch rate of boron nitride which comprises doping a layer of boron nitride with an element from Group IVA of the Periodic Table of the Elements, such as silicon, carbon, or germanium. The doped boron nitride layer can be wet etched at a faster rate with hot phosphoric acid than was possible prior to doping the boron nitride.

A capacitorless dram device on silicon-on-insulator substrate

Abstract: A DRAM device has a first semiconductor region (18) of one conductivity on the silicon film of a silicon-on-insulator substrate (22). A second (16) and a third (14) semiconductor region of the opposite conductivity are formed in the first semiconductor region (18). A fourth semiconductor region (12) of the same conductivity type as the first semiconductor region (18) is formed within the second semiconductor region (16) with higher doping concentration. A insulating layer (11) is formed on the semiconductor surface. On top of the insulating layer (11), a gate electrode (10) is formed and is at least partially overlapped with the first (18), the second (16), the third (14), and the fourth (12) semiconductor region. A storage node (24) is formed in the first semiconductor region (18) between the second (16) and the third (14) semiconductor region where the information is stored. The amount of charge stored in the storage node (24) is controlled by a first transistor including the fourth semiconductor region (12), the second semiconductor region (16), the storage node (24), and the gate electrode (10).

Semiconductor device including a plurality of thin film transistors at least some of which have a crystalline silicon film crystal-grown substantially in parallel to the surface of a substrate for the transistor

Abstract: Nickel is introduced to a predetermined region of a peripheral circuit section, other than a picture element section, on an amorphous silicon film to crystallize from that region. After forming gate electrodes and others, sources, drains and channels are formed by doping impurities, and laser is irradiated to improve the crystallization. After that, electrodes/wires are formed. Thereby an active matrix type liquid crystal display whose thin film transistors (TFT) in the peripheral circuit section are composed of the crystalline silicon film whose crystal is grown in the direction parallel to the flow of carriers and whose TFTs in the picture element section are composed of the amorphous silicon film can be obtained.

Doping of a quantum dot

Abstract: The doping of a quantum dot is an important issue particularly because the luminescence of porous silicon has been attributed to quantum confinement. Since electrochemical etching and possible electroluminescence devices are intimately connected with extrinsic conduction, the quantum size effect on doping, including interactions with induced charges at the dielectric discontinuity, requires investigation.

Hydrogenation of p‐type gallium nitride

Abstract: Hole concentrations of up to 1019 cm−3 have been reported for GaN:Mg films grown by molecular beam epitaxy without any post‐growth treatment. Comparing results from Hall measurements and secondary ion mass spectrometry, we observe doping efficiencies of up to 10% at room temperatures in such p‐type material. By hydrogenating at temperatures above 500 °C, the hole concentration can be reduced by an order of magnitude. A new photoluminescence line at 3.35 eV is observed after this treatment, both in p‐type and unintentionally doped n‐type material, which suggests the introduction of a hydrogen‐related donor level in GaN.

Ultrafast 1.55‐μm photoresponses in low‐temperature‐grown InGaAs/InAlAs quantum wells

Abstract: Doping with Be was found to be very effective for shortening of carrier lifetime in InGaAs/InAlAs multiple quantum wells (MQWs) grown at low temperature by molecular beam epitaxy. The MQW materials have carrier lifetimes controllable from a few tens of picoseconds to 1 ps in the 1.55‐μm wavelength region, coupled with a large optical nonlinearity due to an excitonic feature, implying applicability to ultrafast optical devices in the fiber‐optic communication. The carrier lifetime was measured by a time‐resolved pump‐probe method using an optical source based on a 1.535‐μm semiconductor laser. We also investigated the resistivity, carrier density, and Hall mobility in the MQWs.

Structural and FTIR spectroscopic studies of gel-xerogel-oxide transitions of SnO 2 and SnO 2 : Sb powders and dip-coated films prepared via inorganic sol-gel route

Abstract: Sb doped and undoped SnO2 thin solid coatings were prepared by the dip-coating technique via the sol-gel route. Aqueous gels of undoped compound were made by using a SnCl4 precursor and doping was achieved through the addition of SbCl3 in the concentration range 1–10 mol%. Fourier transform infrared (FTIR), ATR and near normal reflectance spectroscopic techniques were utilized to determine the vibrational spectra of aqueous gels, xerogels and oxides of Sb doped and undoped compounds. Analysis of the corresponding FTIR spectra revealed the existence of Sb-O modes at 770 cm−1. The drying of both types of gel was accompanied by the formation of hydrogen bonds of medium strength wit the OH-O length about 2.7–2.8 A. Some properties of pure and Sb doped oxide powders formed in the temperature range ≤1000°C were measured by the thermogravimetry, X-ray diffraction and FTIR spectroscopic techniques. The doping brought about a broadening of the X-ray diffraction peaks. The reflectivity of the samples increased in the spectral range 4000-600 cm−1 up to 60%, due to the formation of plasma modes. Thin solids films were made by the dip-coating method. The efficiency of the dip-coating process was 0.02–0.1 μm per dipping, depending on the viscosity of the gel. The electrical resistivity of the doped SnO2 coatings was about 1.2 × 10−2 ω cm and thus comparable to the electrical resistivity of the alkoxide derived Sb doped SnO2. Doping decreased visible transmittance ∼5% but infrared reflectance increased up to 40%, depending on the film thickness.