Showing papers on "Doping published in 1993"

Effects of altervalent cation doping of titania on its performance as a photocatalyst for water cleavage

Abstract: The influence of altervalent cation doping of TiO[sub 2] on its performance as a photocatalyst in water cleavage is investigated. It is shown that under illumination in the near-UV region (250--400 nm), platinized anatase TiO[sub 2] exhibits H[sub 2] production rates which are significantly higher than those of the rutile form. Photocatalytic efficiency is shown to be independent of the specific surface area of the semiconductor Incorporation of cations of valence higher than that of the parent cation (W[sup 6+], Ta[sup 5+], Nb[sup 5+]) into the crystal matrix of TiO[sub 2] results in enhanced rates of water cleavage while the opposite is observed upon doping with cations of lower valence (In[sup 3+], Zn[sup 2+], Li[sup +]). The enhancement or reduction of photocatalytic activity is found to be dependent on the concentration and valence of the doping cations. These results do not correlate with observed alterations in the light-absorption capacity of the doped semiconductor. They are explained in term of alteration of the bulk electronic structure of the semiconductor, which influences its electron-hole generation and separation capacity, under illumination. 28 refs., 7 figs., 2 tabs.

Light-emitting gallium nitride-based compound semiconductor device

Abstract: A light-emitting gallium nitride-based compound semiconductor device of a double-heterostructure. The double-heterostructure includes a light-emitting layer formed of a low-resistivity In x Ga 1-x N (0

Transparent conductive electrodes for electrochromic devices: A review

Abstract: This paper reviews the optical and electrical performance of thin films that are useful as transparent electrodes in electrochromic devices. The properties of certain heavily doped wide-bandgap semiconductor oxides (especially In2O3:Sn) and of certain coinage metal films are discussed.

Doping in III-V Semiconductors

Abstract: Doping of III-V semiconductors is an essential part of growth and processing technology for optoelectronic and high speed electronic devices. This review covers several recent developments in III-V doping including (i) the high-concentration regime for p-type dopants in InP and GaAs, (ii) the sensitivity of doping incorporation on the crystal orientation, (iii) compensation mechanisms in Si-doped GaAs, and (iv) p-type carbon doping in GaAs and AlxGa1-xAs.

Doping in III-V Semiconductors

Abstract: Doping of III-V semiconductors is an essential part of growth and processing technology for optoelectronic and high speed electronic devices. This review covers several recent developments in III-V doping including (i) the high-concentration regime for p-type dopants in InP and GaAs, (ii) the sensitivity of doping incorporation on the crystal orientation, (iii) compensation mechanisms in Si-doped GaAs, and (iv) p-type carbon doping in GaAs and AlxGa1-xAs.

First-principles calculations of solubilities and doping limits: Li, Na, and N in ZnSe.

Abstract: We present a comprehensive theoretical approach to determine concentrations of dopant impurities in semiconductors. The formalism is applied to the problem of acceptor doping in ZnSe. Formation energies and concentrations of impurities and native defects are expressed as a function of chemical potentials, for which experimentally accessible ranges are calculated. We show that limitations in the achievable hole concentrations can be explained by two mechanisms: one is the competition between various substitutional and interstitial configurations (compensation), the other is the solubility limit imposed by formation of other phases. Nitrogen is most promising among the dopants examined.

Photochemical switching of polarization in ferroelectric liquid-crystal films

Abstract: LIQUID crystals have been used extensively as active media in display devices such as full-colour television screens These devices are generally based on changes in the arrangement of the liquidcrystal molecules induced by electric fields, which change their optical properties1 Ferroelectric liquid crystals2,3 exhibit spontaneous polarization and therefore show a faster response to changes in the applied field Switching of this field causes a reversal in the direction of polarization2–;5 Here we report polarization switching in ferroelectric liquid crystals driven by a photochemical process The liquid-crystal films are doped with a photochromic compound which undergoes trans–cis isomerization on irradiation Photoisomerization induces a change in the switching potential of the host liquid-crystal film, and thereby causes switching at the irradiated sites The process is fast, stable, reversible and repeatable, and should be exploitable in device applications

Silicides for integrated circuits: TiSi2 CoSi2

Abstract: Silicides have been a topic of intensive research for more than a decade. The driving force for these investigations has certainly been the interesting materials aspects of the silicides and their applications in integrated circuits. The advantages of easy formability and low resistivity for both CoSi2 and TiSi2 have led to an intensive use of these silicides in self-aligned processes for simultaneous silicidation of source, drain and gate. The fundamental investigations of these silicides include thermodynamic and kinetic aspects of phase formation, interactions with doped Si and related defect generation, and the interaction with oxide and metals. Specific issues related to the technological implementation of silicides in a full process will be discussed in view of the trend to scale the silicided area both in the vertical and in the lateral dimensions.

Properties of Lattice-Matched and Strained Indium Gallium Arsenide

Abstract: The semiconductor InGaAs (indium gallium arsenide) plays a pivotal role in the study of quantum systems which provide promising applications in the fields of microelectronics and optoelectronics. This reference explores recent developments with InGaAs. Leading researchers from the USA, Europe and Japan cover such issues as structural, thermal, mechanical and vibrational properties, the band structure of lattice-matched and strained alloys, transport and surface properties, radiative and non-radiative recombinations, expitaxial growth, doping, etching of InGaAs and related heterostructures, photodetectors, FETs, double heterostructure and quantum well lasers.

High-efficiency pyrromethene doped solid-state dye lasers

Abstract: Successful laser oscillation of various pyrromethene dyes doped in a modified acrylic plastic has been achieved. Pumped with a frequency doubled Nd:YAG laser at 532 nm, a slope efficiency of 85% has been obtained from one of the dyes in plastic, with an output beam energy of 128 mJ. A useful lifetime of greater than 20 000 shots at 3.33 Hz with output energies above 30 mJ has been demonstrated, with only a 34% loss in the available output energy.

Gallium antimonide device related properties

Abstract: The physical properties of GaSb are briefly presented and the device implications reviewed. GaSb is a direct gap semiconductor (0.72 eV) capable of being doped either p or n type with good mobilities and it has significant electro-optical potential in the near IR range. As a substrate, or active layer, GaSb can be employed in conjunction with many semiconductors such as (AlGa)Sb or In(AsSb) and has interesting heterojunction potential for detectors and lasers and quantum well structures.

Schottky barrier photodetector based on Mg‐doped p‐type GaN films

Abstract: In this letter we report the fabrication and characterization of Schottky barrier photodetectors on p‐type GaN films. These films were grown over basal plane sapphire substrates using low pressure metalorganic chemical vapor deposition and magnesium as the p‐type dopant. The current‐voltage and capacitance‐voltage characteristics were measured for Ti/Au Schottky barriers for a film with a p doping of 7×1017 cm−3. We measured a 1.5 V forward turn on and a 3 V reverse breakdown. The zero bias responsivity of a detector with 1 mm2 area was measured to be 0.13 A/W. For these photovoltaic detectors, the photoresponse was nearly constant from 200 to 365 nm and fell sharply by several orders of magnitude for wavelengths above 365 nm.

Study of the effect of Sn doping on the electronic transport properties of thin film indium oxide

Abstract: High quality, low resistivity (2.6×10−4 Ω cm), 0.32‐μm‐thick amorphous and polycrystalline, pure and Sn‐doped, In2O3 films prepared by high density plasma‐assisted electron beam evaporation were used to investigate the effect of Sn doping on the electronic transport properties of this material. Amorphous films with high carrier density in the as‐deposited state showed no effect of Sn doping on resistivity (ρ), Hall mobility (μ), or carrier density (n) over the range 0 to 5.3 wt % Sn. After recrystallization by annealing in air at 180 or 250 °C for 20 min, n, μ, and ρ were seen to be strongly dependent on Sn concentration in the range 0 to 1.5 wt % with a decreasing effect of Sn doping in the range 1.5 to 5.3 wt %. The data presented in this study were analyzed based on charged and neutral impurity scattering models and suggest that increasing Sn concentration leads to the formation of defect complexes which act as scattering centers but which do not contribute carriers to the material.

Semiconductor quantum dot light emitting/detecting devices

Abstract: A semiconductor light emitting/detecting device has a first doped silicon layer, an intrinsic silicon epitaxial layer formed on the first doped silicon layer, at least one quantum dot embedded within the intrinsic silicon epitaxial layer, and a second doped silicon layer formed on the second intrinsic silicon epitaxial layer.

Toward a unified magnetic phase diagram of the cuprate superconductors.

Abstract: We propose a unified magnetic phase diagram of the cuprate superconductors. A new feature of this phase diagram is a broad intermediate doping region of quantum-critical, z=1, behavior, characterized by temperature independent ${\mathit{T}}_{1}$T/${\mathit{T}}_{2\mathit{G}}$ and linear ${\mathit{T}}_{1}$T, where the high energy spin waves are not overdamped. The spin gap in the moderately doped materials is related to the suppression of the spectral weight for frequencies smaller than ${\mathrm{\ensuremath{\Delta}}}_{\ensuremath{\xi}}$=c/\ensuremath{\xi} in the quantum disordered, z=1, regime. The crossover to the z=2 regime, where ${\mathit{T}}_{1}$T/${\mathit{T}}_{2\mathit{G}}^{2}$\ensuremath{\simeq}const, occurs only in the fully doped materials.

Accurate measurements of the silicon intrinsic carrier density from 78 to 340 K

Abstract: The intrinsic carrier density in silicon has been measured by a novel technique based on low‐frequency capacitance measurements of a p+‐i‐n+ diode biased in high injection. The major advantage of the method is its insensitivity to uncertainties regarding the exact values of the carrier mobilities, the recombination parameters, and the doping density. The intrinsic carrier density was measured in the temperature range from 78 to 340 K. At 300 K the value of ni was found to be (9.7±0.1)×109 cm−3.

Role of photoinduced defects in amorphous GexSe1−x photoconductivity

Abstract: The spectral dependence of photoconductivity of amorphous pure Se and GeSe alloys (4 and 8 at.% Ge) evaporated thin films was measured for a spectral range between 250 and 800 nm. A comparison of the Se and GeSe spectra shows that the magnitude of photocurrent decreases as the Ge content increases. This result indicates a correlation between the magnitude of the photocurrent and the density of photoinduced defects. The contribution of these defects to the enhancement of photoconductivity in a specific region of the spectrum as well as the influence of temperature on their density are also discussed.

Growth of doped semiconductor monolayers

Abstract: A cycle of alternately or cyclically introducing external gases containing molecules of component elements of a compound semiconductor to be formed on a substrate is repeated while appropriately controlling the pressure, substrate temperature and gas introduction rate in a crystal growth vessel, so that a monocrystal which is dimensionally as precise as a single monolayer can grow on the substrate by making use of chemical reactions on the heated substrate surface. Doped molecular layer epitaxy of a compound semiconductor comprising individual steps of introducing and evacuating a first source gas, introducing and evacuating a second source gas, and introducing and evacuating an impurity gas which contains an impurity element. The doped impurity concentration varies almost linearly with the pressure during doping in a wide range.

Study of superconductivity in the Hg-Ba-Ca-Cu-O system

Abstract: The high temperature superconducting Hg-Ba-Ca-Cu-O (HBCCO) compound system reported by Schilling et al. has been reproduced with an onset transition-temperature ( T c0 ) up to ≁140 K and a main transition at ≁135 K, after proper heat-treatment. We found a positive pressure-effect on T c with a rate of 0.17 to 0.18 K/kbar and an irreversibility line at temperatures higher than that in the double Bi and Tl layered high temperature superconductors (HTS's). The observation suggests that the compounds synthesized by us are underdoped and further T c enhancement (although not drastic) is possible by proper doping, and the HBCCO system appears to be a better candidate than the double Bi and Tl layered HTS's for applications based on the higher irreversibility line.

Method for forming an insulated gate field effect transistor

Abstract: In an inverted stagger type thin-film transistor, the preparing process thereof can be simplified, and the unevenness of the thin film transistor prepared thereby can be reduced That is, disclosed is a preparing method which comprises selectively doping a semiconductor on a gate insulating film with an impurity to form source, drain, and channel forming regions, and conducting a laser annealing to them, or a preparing method which comprises selectively doping the semiconductor region with an impurity by a laser doping method

Solid-state absorption spectroscopy of alkyl-substituted oligothiophenes

Abstract: We have investigated the absorption spectra of thin solid films of alkyl-substituted oligothiophenes in both the neutral and doped states over a photon energy range of 0.05-5.0 eV. In the neutral state these oligomers display the π-π * transition bands in the near-UV to visible region with fine structures on the low-energy side. We found two different oxidized states for the doped species; the lower state is characterized by two subgap bands in the near-IR region that are induced upon doping and the higher state by only one band. In the two oxidized species, the π-π * band exhibits increasing intensity on the lower energy side at increasing doping levels and, finally, the absorption maximum is shifted to a low-energy region at the highest doping levels