Showing papers on "Doping published in 1995"

Polymer Light-Emitting Electrochemical Cells

Abstract: A device configuration for light emission from electroactive polymers is described. In these light-emitting electrochemical cells, a p-n junction diode is created in situ through simultaneous p-type and n-type electrochemical doping on opposite sides of a thin film of conjugated polymer that contains added electrolyte to provide the necessary counterions for doping. Light-emitting devices based on conjugated polymers have been fabricated that operate by the proposed electrochemical oxidation-reduction mechanism. Blue, green, and orange emission have been obtained with turn-on voltages close to the band gap of the emissive material.

Metal oxide semiconductor device forming a pn junction with a thin film transistor of metal oxide semiconductor of copper suboxide and manufacture thereof

Abstract: PURPOSE: To obtain an excellent PN junction by doping controlled metal oxide semiconductor with impurities, by controlling defects by introducing hydrogen or the like in the defects due to the excessive oxygen in a part of metal oxide semiconductor of copper suboxide or the like, and controlling the carrier density and the conductivity type. CONSTITUTION: A metal oxide semiconductor 25 is metal semiconductor obtained by oxidizing metal films 24, 24'. An insulating protective film is formed on the surfaces of an insulating film 26 and the metal oxide semiconductor 25. By leading out electrodes connected with source drain electrodes 24, 24', a transistor having a gate electrode 22 is formed. The carrier density and the conductivity type are controlled by eliminating oxygen defects. The P-type conductivity or the N-type conductivity, and the resistivity can be controlled by impurity doping. In these cases, ion implantation method or the like can be applied. Thereby a thin film transistor of high mobility can be formed in a large area by low temperature treatment.

A critical review of ohmic and rectifying contacts for silicon carbide

Abstract: For more than three decades, SiC has been investigated as a wide band gap semiconductor. This paper reviews ohmic and rectifying metal contacts on n- and p-type α- and β-SiC reported throughout that time period. Electrical characteristics, Schottky barrier heights (SBHs), thermal stability, and chemical reactions are discussed. Most metals formed very good rectifying contacts in the as-deposited condition on both n- and p-type 6H-SiC with Schottky barrier heights ⪖ 1 eV. Low ideality factors (n 1100 V) have been displayed in this material. The electrical properties of contacts on 3C-SiC have been more dependent on the quality of the 3C-SiC films, which have been plagued by higher defect densities than 6H-SiC. In general, a partial pinning of the Fermi level has been evidenced by positive correlations, which are less than 1 (≈ 0.2–0.6), between the SBHs and the metal work functions. Ohmic contacts with low contact resistivities (⪕ 10−5 Ω cm2), especially important for high power applications, on any of the SiC polytypes have been exceptionally difficult to achieve. Most of the ohmic contacts have relied on high doping concentrations in combination with annealing at temperatures between 800 and 1300 °C. Annealed Ni and Al have primarily been used in ohmic contact metallizations for n- and p-type SiC, respectively. The tendency of SiC to react with metals to form carbides and/or silicides at potential device operating temperatures ( ∼ 600 °C) can be a problem for potential long term applications at high temperature. These critical issues are discussed along with future perspectives for research approaches.

Lattice Parameters and Densities of Rare‐Earth Oxide Doped Ceria Electrolytes

Abstract: Lattice parameters and densities of various rare-earth oxide doped ceria were measured. For the calculation of lattice parameters, the concept of the oxygen vacancy radius was introduced. The estimated oxygen vacancy radius was 1.164 {angstrom} for trivalent, rare-earth oxide doped ceria and 0.993 {angstrom} for zirconia. The modeling of the lattice parameter and density based on the oxygen vacancy radius generally agreed with experimental results. The density measurements illustrate that oxygen vacancy formation is the predominant defect reaction. Evidence of some interstitial contribution was also noted for smaller-sized dopant cations such as Yb{sup 3+} and Er{sup 3+}.

Green luminescence from copper doped zinc sulphide quantum particles

Abstract: Free‐standing powder of zinc sulphide quantum particles has been synthesized using a chemical route. X‐ray diffraction analysis shows that the diameter of the particles is ∼21±2 A which is smaller than the Bohr exciton diameter for zinc sulphide. UV absorption shows an excitonic peak centered at ∼300 nm corresponding to an energy gap of 4.1±0.1 eV. These particles show a luminescence band at ∼424 nm. The quantum particles could be doped with copper during synthesis without altering the UV absorption or x‐ray diffraction pattern. However, doping shifted the luminescence to 480 nm, green wavelength in the visible region.

Zinc‐indium‐oxide: A high conductivity transparent conducting oxide

Abstract: We report the fabrication and characterization of zinc‐indium‐oxide films with similar electrical conductivity and better transparency in both the visible and infrared compared with indium–tin–oxide, a widely used transparent conductor in many technological applications. Dramatically superior transmission properties in the 1–1.5 μm range in particular make zinc–indium–oxide attractive for use in infrared devices, where transparent electrodes are required. Resisitivities as low as 400 μΩ cm result from doping with small quantities of Sn; Al, Ga, and Ge are also effective dopants. Deposition on glass and quartz substrates as amorphous films by pulsed laser deposition and dc reactive sputtering is described.

Gallium nitride group compound semiconductor laser diode

Abstract: A gallium nitride group compound semiconductor laser diode includes at least one pn junction layer disposed between an n-type layer and a p-type layer. The n-type layer is formed from a gallium nitride group compound semiconductor material defined by the composition equation (Alx Ga1-x)y In1-y N (where 0≦x≦1 and 0≦y≦1). The p-type layer, doped with an acceptor impurity, is obtained by electron beam irradiating a gallium nitride group compound semiconductor material defined by the composition equation (Alx' Ga1-x')y' In1-y' N (where 0≦x'≦1, 0≦y'≦1, x=x' or x≠x', and, y=y' or y≠y'). The improved gallium nitride group semiconductor laser diode of the present invention is found to emit light in the visible short wavelength spectrum of light which includes the blue, violet and ultraviolet regions.

The roles played by Ag and Al dopants in controlling the electrical properties of ZnO varistors

Abstract: Four sets of ZnO‐based ceramic varistors (reference samples‐ZNR; doped with aluminium‐AL; doped with silver‐AG; doped with aluminium and silver‐AA) have been prepared by the conventional mixed oxide route. The current‐voltage (I‐V) characteristics, determined at current densities up to 1 mA/cm2, yielded nonlinear coefficients (α) of 38, 60, 22 and 56, respectively. Dc and ac degradation tests were performed at 115 °C. Ac impedance analysis was used to determine grain (rg) and grain boundary (Rb) resistances; capacitance‐voltage analysis enabled the donor density (Nd) and the barrier height (φ) to be determined. Doping the varistors with Al increased Nd, reduced rg, and improved the I‐V characteristics, but caused an increase in Zn interstitials which degraded the stability. In contrast, Ag acts as an amphoteric dopant in ZnO causing a decrease in Nd, an increase in rg and Rb, and a reduction in α ; Ag located in the interstitial sites is able to block the formation and migration of new Zn interstitials, ...

Two‐dimensional surface dopant profiling in silicon using scanning Kelvin probe microscopy

Abstract: A simultaneous combination of scanning Kelvin probe microscopy and scanning atomic force microscopy has been applied to the problem of profiling dopant concentrations in two dimensions in silicon microstructures. By measuring the electrochemical potential difference which minimizes the electrostatic force between probe tip and sample surface, the work‐function difference between the tip and surface is estimated. To the extent that this work‐function difference is a consequence of the dopant concentration at or near the sample surface, doping profiles are inferred from the measurement. Structures examined and presented here include contact holes, and the technologically significant lightly doped drain of a metal–oxide–silicon field‐effect transistor. Using this methodology, one can distinguish relative changes in dopant concentration with lateral resolution less than 100 nm. Sample preparation is minimal, and measurement time is fast compared to other techniques. The measurements have been compared to predictions based on two‐ and three‐dimensional process and device simulation tools. The comparisons show that the technique is sensitive to changes in dopant concentration, from ≊1015 to 1020 cm−3, of less than 10% at these size scales. Suggestions to resolve absolute dopant concentration are made.

Electron field emission from ion‐implanted diamond

Abstract: Diamond films and islands grown by chemical vapor deposition were implanted with boron, sodium, and carbon ions at doses of 1014–1015/cm2. This structural modification at the subsurface resulted in a significant reduction of the electric field required for electron emission. The threshold field for producing a current density of 10 mA/cm2 can be as low as 42 V/μm for the as‐implanted diamond compared to 164 V/μm for the high quality p‐type diamond. When the ion‐implanted samples were annealed at high temperatures in order to anneal out the implantation‐induced defects, the low‐field electron emission capability of diamond disappeared. These results further confirm our earlier findings about the role of defects in the electron emission from undoped or p‐type doped diamond and indicate that the improved emission characteristics of as‐implanted diamond is due to the defects created by the ion implantation process.

Glass matrix doped with activated luminescent nanocrystalline particles

Abstract: A luminescent glass includes nanocrystalline semiconductor particles, such as ZnS nanocrystals, and an activator, such as copper, for the particles. The glass is made by depositing the nanocrystalline semiconductor particles and the activator within a porous glass matrix, such as 7930 VycorTM and then thermally activating the glass. The porous glass matrix may be at least partially consolidated or may be allowed to remain porous. The nanometer particle size permits the luminescent glasses of the present invention to be transparent to its luminescent emsissions.

How can sensitive and selective semiconductor gas sensors be made

Abstract: In this paper the theoretical and practical background of the realization of highly sensitive and selective semiconductor gas sensors is discussed. This discussion is based on the literature and some earlier published experimental results. The most important items are the quality of the semiconductor surface, the role of additives (catalytically active materials), the size of crystals or the layer thickness compared to the Debye length of the semiconductor, the quality of the interface between semiconductor crystals and the interface between the semiconductor and the grain of doping material (potential barriers). All of the listed factors depend on the technology; some of them depend on the temperature, as well as the characteristics of the realized sensor or sensor system.

Semi‐insulating 6H–SiC grown by physical vapor transport

Abstract: Semi‐insulating 6H–SiC crystals have been achieved by using controlled doping with deep‐level vanadium impurities. High resistivity undoped and semi‐insulating vanadium‐doped single‐crystals with diameters up to 50 mm were grown by physical vapor transport using an induction‐heated, cold‐wall system in which high purity graphite materials constituted the hot zone of the furnace. Undoped crystals were p‐type due to the presence of residual acceptor impurities, mainly boron, and exhibited resistivities ranging up to 3000 Ω cm. The semi‐insulating behavior of the vanadium‐doped crystals is attributed to compensation of residual acceptors by the deep‐level vanadium V4+(3d1) donor located near the middle of the band gap.

Transistor and process for fabricating the same

Abstract: A process for fabricating a thin film transistor, which comprises crystallizing an amorphous silicon film, forming thereon a gate insulating film and a gate electrode, implanting impurities in a self-aligned manner, adhering a coating containing a catalyst element which accelerates the crystallization of the silicon film, and annealing the resulting structure at a temperature lower than the deformation temperature of the substrate to activate the doped impurities. Otherwise, the catalyst element can be incorporated into the structure by introducing it into the impurity region by means of ion implantation and the like. Also a process for fabricating a thin film transistor, which comprises forming a gate electrode, a gate insulating film, and an amorphous silicon film on a substrate, implanting impurities into the amorphous silicon film to form source and drain regions as the impurity regions, introducing a catalyst element into the impurity region by adhering a coating containing the catalyst element of by means of ion doping and the like, and annealing the resulting structure at a temperature lower than the deformation temperature of the substrate to activate the doped impurities.

Manganese doped zinc sulphide nanoparticles by aqueous method

Abstract: Zinc sulphide nanoparticles in the size range ∼10–40 A diameter have been synthesized using the aqueous chemical method. Scanning tunneling microscopy showed that particles are indeed nanosize particles. The size dependent band gap could be varied from a bulk value of 3.68 to 4.5 eV. X‐ray diffraction indicated that nanoparticles are crystalline except for those with band gap ∼4.5±0.1 eV. Nanoparticles with particle size ∼21×2 A diameter or energy gap 4.1×0.1 eV were doped with manganese. The photoluminescence peak at ∼600 nm corresponding to yellow light emission was observed. Atomic absorption studies show that maximum luminescence intensity is achievable with 0.12 at. wt % of Mn doping.

Absence of superconductivity in the doped antiferromagnetic spin-ladder compound (La,Sr)CuO2.5

Abstract: A SPIN-½ Heisenberg antiferromagnetic ladder is a model system comprising parallel chains of interacting elemental spins. Spin ladders having an even number of chains have been predicted1a¤-6 to exhibit interesting dynamics, including superconductivity, when unoccupied spin sites are introduced along the chain (that is, when the chains are doped with holes). Spin-ladder models thus provide a novel potential mechanism for high-temperature superconductivity in real materials. But unfortunately materials with spin-ladder structure are quite rare4a-10, and the few known compounds have not previously been doped successfully with holes. Here we report the high-pressure synthesis of a new hole-doped two-chain ladder compound, La1a¤-xSrxCuO2.5. We have observed a marked insulator-to-metal transition in this compound with increased doping, but no superconducting transition down to 5 K. The absence of superconductivity in this material must be reconciled with theoretical predictions based on ideal hole-doped spin-ladder models.

Electronic structure of antimony-doped tin oxide.

Abstract: The electronic structure and associated properties of antimony-doped tin (IV) oxide have been studied using both the self-consistent-field scattered-wave molecular-orbital cluster approach and the augment- ed-spherical-wave supercell band-structure approach. The calculated molecular-orbital energy eigenvalues and wave functions have been used to interpret several interesting optoelectronic properties of this defect semiconductor. The nature and origin of the energy gap from optical-absorption studies and the valence-band structure from ultraviolet photoelectron spectroscopy (UPS) have been satisfactorily explained using the band structure of pure and antimony-doped tin oxide. It is observed that the antimony ion leads to an impurity band in the band gap and increases the forbidden gap of the host material. This partially filled free-electron-like band is the origin of the UPS peak near the band edge whose intensity grows with the dopant concentration.

Photoconductive ultraviolet sensor using Mg‐doped GaN on Si(111)

Abstract: This work characterizes a GaN:Mg on silicon ultraviolet photodetector with a cutoff at 3.3 eV and a responsivity of 12 A/W at 4 V bias for optical intensities on the order of 1 W/m2 and below. A weak photovoltaic response is also reported. The photocurrent is nearly linear versus optical intensity for up to 10 W/m2. The responsivity increases nearly linearly with applied voltage up to 8 V, then the increase slows toward saturation. To explain this high responsivity in a direct gap semiconductor, it is hypothesized that holes are captured at either compensated Mg deep acceptor sites or Mg‐related trap/recombination centers, resulting in a greatly prolonged electron free‐carrier lifetime.

Semiconductor Optoelectronics: Physics and Technology

Abstract: Semiconductors - crystal structure properties of semiconductors - electronic doping and carrier transport optical propetries of semiconductors excitonic effects and modulation semiconductor junction theory optoelectronic detectors noise and the photoreceiver the light emitting diode laser diode - static properties semiconductor lasers - dynamic properties modulation and switching devices optical communication systems list of symbols important properties of semiconductors important quantum mechanics concepts bipolar transistor action optical waves in waveguides and crystals.

CCl4 doping of GaN grown by metalorganic molecular beam epitaxy

Abstract: Hole concentrations up to 1017 cm−3 are achieved in GaN doped with C from a CCl4 source during metalorganic molecular beam epitaxy at 700 °C. The hole mobility under these conditions is 103 cm2 V−1 s−1 at 300 K. The deposition rate of the GaN is reduced by addition of CCl4 to the growth chemistry even at low flow rates and net etching is observed for a halocarbon flow above 1.1 sccm under our conditions. Annealing up to 800 °C did not increase the hole concentration indicating that residual hydrogen passivation of the acceptors is not significant when employing a He carrier gas for transporting the group III metalorganic precursor (triethylgallium).

Nanometer‐scale field‐induced oxidation of Si(111):H by a conducting‐probe scanning force microscope: Doping dependence and kinetics

Abstract: Hydrogen‐terminated Si(111) was patterned on the nanometer scale by field‐induced oxidation using a biased conducting‐probe scanning force microscope. The kinetics of oxide growth as well as its dependence on doping are investigated. Field‐induced oxidation is observed for voltages exceeding a doping dependent threshold above which oxidation kinetics follows a power law.

Electroluminescence from single layer molecularly doped polymer films

Abstract: Light emission from single layer thin film devices comprised of a hole transport polymer, poly(N-vinylcarbazole) (PVK) doped with 2-(4-biphenyl)-5-(t.-butylphenyll1,3,4-oxadiazole (Bu-PBD) and variety of emitter molecules is described. The single layer nature and the use of soluble materials simplifies the fabrication of devices by common solution coating techniques. The color of the emitted light can be tuned across the visible spectrum by using appropriate dyes. Evidence is presented that the luminance from any given device increases linearly with the current density and that the luminance observed from different devices is independent of the hole mobility. This shows that the critical determinant of the light output is the quality of the injecting contact or the number of injected carriers and not the speed with which the carriers migrate. Some criteria for tuning the emission color are presented.

Transistor device employing crystallization catalyst

Abstract: A thin film transistor includes a crystallized amorphous silicon film having a gate insulating film and a gate electrode formed thereon. The device includes impurities implanted in a self-aligned manner and a catalyst that accelerates the crystallization of the silicon film. The catalyst is introduced in the silicon film by adhering a coating containing the catalyst element and annealing the resulting structure at a temperature lower than the deformation temperature of the substrate to activate the doped impurities. The catalyst element can also be incorporated into the silicon film by means of ion implantation and the like. Also disclosed is a thin film transistor, which comprises a gate electrode, a gate insulating film, an amorphous silicon film having impurities implanted therein to form source and drain regions as the impurity regions, and a catalyst element introduced into the impurity regions by adhering a coating containing the catalyst element or by means of ion doping and the like, wherein the resulting structure is annealed at a temperature lower than the deformation temperature of the substrate to activate the doped impurities.

Study of defect states in GaN films by photoconductivity measurement

Abstract: Optical absorption by defect states in gallium nitride (GaN) films was studied by photoconductivity (PC) spectroscopy at room temperature. A number of undoped n‐type and Mg‐doped p‐type samples were employed in the present study. The PC response per absorbed photon decreased by more than four orders of magnitude as GaN became p‐type conducting. Furthermore, all the samples exhibit PC response at photon energies far below the band gap energy of GaN. The optical absorption increases with photon energy hν from 1.5 to 3.0 eV approximately as exp(hν/E0). The parameter E0 ranges from 180 to 280 meV, and is considerably smaller for the insulating p‐type sample. For a p‐type conducting sample, the PC response is flat between 0.7 and 1.4 eV. A model for the density of states distribution in the forbidden gap of GaN and the effect of Mg doping is proposed.