Showing papers on "Organic semiconductor published in 1994"

Organic conductors : fundamentals and applications

Abstract: Organic Conductors: An Overview. Basic Physical Concepts of Organic Conductors. Molecular Design of Organic Conductors. Chemical Synthesis and Crystal Growth Techniques. Organic Conductors: The Crystallographic Approach. Optical Properties. Magnetic, ESR, and NMR Properties. Organic Semiconductors. Organic Metals. Organic Superconductors: From (TMTSF)2PF6 to Fullerenes. Introduction to Conjugated and Conducting Polymers. Undoped (Semiconducting) Conjugated Polymers - From Structure and Electronic Properties to Applications. Doped Conjugated Polymers: Conducting Polymers. Related Topics I: Charge-Transfer Complexes in Biological Systems. Related Topics II: Thallium-Based High-T, Superconducting Oxides: A Summary. Applications of Organic Conductors: Molecular Electronics. Organic Photoconductors and Photovoltaics.

Color variation with electroluminescent organic semiconductors in multimode resonant cavities

Abstract: The range of possibilities in controlling the color of an organic semiconductor based light emitter diode (LED) by incorporating the active layers in a multimode Fabry–Perot cavity is demonstrated. The combination of carefully designed multimode microcavities and electroluminescent organic semiconductors makes possible the realization of mixed colors such as white, purple, etc. with a single LED. The parameters affecting the color include the total optical thickness of the device and the position of the electromagnetic‐field antinodes with respect to the location of the emitting dipoles. The electrical characteristics and quantum efficiency of such devices are also reported.

Microcavity effects in organic semiconductors

Abstract: Microcavity structures containing hydroxyquinoline aluminum and diamine layers commonly used in electroluminescent devices are described. We show that it is possible to obtain emission at red, green, and blue wavelengths by changing the thickness of a polyimide filler layer in the cavity. The angular dependence of the emission wavelength and linewidth are reported and the implications for organic electroluminescent color displays are discussed.

Observation of degradation processes of Al electrodes in organic electroluminescence devices by electroluminescence microscopy, atomic force microscopy, scanning electron microscopy, and Auger electron spectroscopy

Abstract: Degradation of top electrodes is one of the most important factors to determine the lifetimes of organic electroluminescence (EL) devices. An organic EL device [indium thin oxide (ITO)/N,N’‐diphenyl‐N,N’‐bis(3‐methylphenyl)‐(1,1’‐biphenyl)‐4, 4’‐diamine (TPD)/tris(8‐hydroxy‐ quinoline)aluminum (Alq3)/Al] was prepared and a morphological change of the Al top electrode was observed during and/or after applying voltage by atomic force microscopy and scanning electron microscopy (SEM). The change in the electrode surface, i.e., the increase in surface roughness was observed during the current flow. The degradation process started from faint dark core parts and propagated into disks with different rates depending on the magnitude of applied voltage. Degraded sites of the Al electrode, which were analyzed as aluminum oxide by Auger electron spectroscopy, protruded into the air on the organic layers. In SEM images of a life‐end electrode, discontinuities due to crevasse formation in the organic layers sandwiched...

Band lineup at an organic-inorganic semiconductor heterointerface : perylenetetracarboxylic dianhydride/gaas(100)

Abstract: We present a photoemission study of the electronic properties of an interface between the organic semiconductor; 3, 4, 9,10 perylenetetracarboxylic dianhydride (PTCDA) and n‐type GaAs(100) We examine the evolution of the interface electron distribution as a function of PTCDA overlayer thickness The highest occupied molecular orbital level of PTCDA is measured at 07±01 eV below the GaAs valence band maximum The PTCDA ionization potential is measured at 64±015 eV The discrepancy between the band alignment deduced from photoemission and transport measurement suggests that interface states or polarization effects play a role in determining the transport properties of the organic‐inorganic heterojunction diodes

Electroluminescence from organic semiconductors in patterned microcavities

Abstract: The authors have fabricated light-emitting diodes with emission peaks from 490 to 630 nm using planar microcavity tailored luminescence from a single organic semiconductor. The optical thickness of the microcavities is controlled with a patterned inert filler. This approach obviates the need to integrate three separate emissive materials in the manufacture of full colour electroluminescent displays.

Structural and electronic properties of an organic/inorganic semiconductor interface: PTCDA/GaAs(100)

Abstract: A study of the formation of an interface between the archetype organic semiconductor, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA), and GaAs(100) is presented. We examine the growth of thin (few monolayers) and thick (up to 3000 A) organic layers are examined at room and low temperature, and conclude that bonding across the PTCDA/GaAs interface is stronger than the PTCDA van der Waals intermolecular bond. Although the molecular stacking distance of 3.21 A is clearly seen in x‐ray diffraction, the films are polycrystalline, and no interface molecular ordering is detected. The interface electronic structure and the energy band lineup are studied with photoelectron spectroscopy. The highest occupied molecular orbital in PTCDA is found at 0.7 eV below the top of the GaAs valence band, in agreement with a vacuum level alignment a this interface.

Organic quantum semiconductor and quantum semiconductor device

Abstract: An organic semiconductor including an organic semiconductor layer, which layer is formed by epitaxially depositing molecules of a compound selected from phthalocyanines to form a super-thin film configuration including one-dimensional columns of stacked molecules in the form of quantum wires separated respectively from each other.

Heterostructures of Crystalline Organic and Inorganic Semiconductors for Applications in Optoelectronic Integrated Circuits

Abstract: Heterostructures of crystalline organic and inorganic semiconductors based on the aromatic compound PTCDA (3, 4, 9, 10-perylenetetracarboxylic dianhydride, C24O6H8) are investigated. Crystal growth by organic molecular beam deposition (OMBD) on different substrates and optical characterization are discussed. Homogeneous crystalline films are attained at low growth rates and substrate temperatures from T=77 K to T=350 K. With regard to applications in optoelectronic integrated circuits (OEICs) waveguide structures, photodetectors and a concept for the integration of these two devices are presented. Due to the low process temperatures optoelectronic devices can be prepared on already processed III-V and silicon wafers.

Photovoltaic conversion efficiency in copper-phthalocyanine/ perylenetetracarboxylic acid benzimidazole heterojunction solar cells

Abstract: Summary form only given. Recently relatively high photovoltaic energy conversion efficiencies of about 1% in heterojunction-type organic solar cells have been reported. No report, however, has appeared that evidenced the possibility of increasing the efficiency exceeding 2%. The origins which prevent further increase of the efficiency in organic heterojunction solar cells have been ascribed to low photon collection efficiency, low quantum efficiency of charge carder generation, high resistivity of organic semiconductors, and so on. Very little quantitative discussion examining the possible origins of depressing the efficiency has been given, except for some earlier analyses on metal-organic semiconductor Schottky-type solar cells. In this report, we will show one of the possible ways to analyze the conversion efficiency of heterojunction solar cells quantitatively using our experimental data on copper phthalocyanine/perylenetetracarboxylic acid benzimidazole haterojunction cells. Our conclusion is that low photon collection efficiency and low open-circuit voltage are the major origins of low conversion efficiency in organic haterojunction-type solar cells. When proper combinations of heterojunciton dyes are carefully selected and thicknesses of organic layers are thin enough, neither quantum efficiency of charge separation nor resistivity of dye layers causes lowering of conversion efficiency.

Production of conductive organic material oriented film and production of organic electronic element with the same

Abstract: PURPOSE:To obtain an organic electronic element large in a carrier transfer degree and excellent in characteristics as a FET element by enhancing the orientation property of a conductive organic compound and using the oriented film of the conductive organic compound. CONSTITUTION:A polytetrafluoroethylene rod 13 is slid on a gate-insulating layer 12 formed on a silicon substrate 11 at a speed of 1mm/sec with a pressure of 1kg/cm in a direction to form a PTFF oriented film 14. The film 14 is covered with a mask for forming a comb type electrode used as an electric source and a drain electrode 15 thereon, and subsequently subjected to the deposition of chromium and gold under a vacuum of 1X10 Torr. While the electrode 15 is partially covered with an aluminum foil, 5,5'- dimethylsesquithiophene (DMSxT) for forming an organic semiconductor layer is vacuum-deposited. The element formation-free side of the substrate is rubbed to use the silicon substrate itself as a gate electrode.

Electrical and photoconductive properties of orientation‐controlled chloroaluminumphthalocyanine thin films

Abstract: Structure dependence of electrical properties was investigated for amorphous and epitaxial thin films of chloroaluminumphthalocyanine vacuum deposited on both glass and KCl. The extrinsic conductivity in the dark was improved by elevating substrate temperatures, depending on the morphological change from granular, discontinuous films deposited at a substrate temperature of 25 °C to uniform, continuous ones at 250 °C. The photocurrents under monochromatic light illumination increased in proportion to the amount of adsorbed O2 in the amorphous films on glass. A regular doping form of O2 in the epitaxial film on KCl could enhance photocarrier generation. The granular, discontinuous morphology in the films caused a frequent charge‐carrier recombination at the grain boundaries and defect sites. In the intrinsic region the amorphous films exhibited a higher dark conductivity due to the π‐electron interaction between the randomly arranged molecules and gave a moderate activation energy for conduction. The epitaxial film with a regular orientation exhibited a significantly higher activation energy for intrinsic dark conduction because of a weak molecular interaction between the standing molecular columns.

Electronic and electrochemical properties of octakis-substituted metallophthalocyanines with donor or acceptor groups

Abstract: Matallophthalocyanine derivatives with octakis-substituents of donor or acceptor groups were synthesized and their electric or electrochemical properties were investigated. These phthalocyanine derivatives gave electric conductivity of 10 −0 ∼10 −4 S/cm and distinct reversible electrochemistry.

Organic/semiconductor superlattices as an attractive perspective

Abstract: Organic/amorphous semiconductor superlattices are built up by means of alternating application of two different methods for thin film formation. Organic sublayers of cadmium arachidate are deposited by means of the Langmuir-Blodgett technique, and inorganic sublayers of amorphous CdSe are grown via the thermal vacuum evaporation method. The details of the superlattice preparation providing deposition of smooth and homogeneous sublayers are described. The periodicity of the structures obtained is evidenced by means of the small-angle X-ray diffraction method. The experimental realization of this new type artificial periodic structures opens a number of possibilities for the combination of the advantages of superthin ordered organic and the semiconductor films. The areas of application of such superlattices are outlined.

Introduction of impurity atom

Abstract: PURPOSE:To provide a method of introducing impurity atoms into diamond or BN or SiC or organic semiconductor CONSTITUTION:Impurity particles are accelerated, energized and are applied to diamond or BN or SiC or organic semiconductor material Diamond or BN or SiC or the organic semiconductor material is exposed to the atmosphere that contains hydrogen radicals or hydrogen ions after irradiated with the accelerated particles

Semiconductor gas sensor

Abstract: PURPOSE:To reduce the thickness and weight of a gas sensor by forming a semiconductor metal oxide film on a thin alumina substrate with a specific thickness. CONSTITUTION:A highly pure alumina substrate 21 whose thickness is 0.03mm or more and 0.4mm or less is manufactured using the sol-gel method using a metal alkoxide. A semiconductor metal oxide film 22 is formed on the substrate 21. The oxide film 22 is composed of an n-type metal oxide or organic semiconductor, preferably of tin oxide. A nichrome resistor film 25 for heating the thin film 22 is formed on a surface which opposes the thin film 22 of the substrate 21. It is desirable that the resistor film 25 should be covered with an insulation material. It is desirable that an electrode 23 formed at both edge parts of the thin film 22 should be gold, platinum, or platinum metal or an alloy of these metals. When ethanol gas is adsorbed by the thin film 22, electrical conductivity of the thin film 22 changes, thus measuring the concentration of ethanol. By heating the thin film 22 with the resistor film 25, the response speed and sensitivity of a gas sensor 20 can be improved.

Manufacture of organic thin-film switching-memory composite element and organic thin-film switching-memory composite element

Abstract: PURPOSE: To provide the manufacture of an organic thin-film switching-memory composite element, in which the dispersion, reproducibility, stability, etc, of switching characteristics are improved and which can also be applied to a large number of organic thin-film elements CONSTITUTION: An element having the structure 2, 3, 4 of a metal/an organic semiconductor thin-film/a metal is exposed in a gas and the gas of the element is discharged, and switching characteristics are improved while stability is increased An organic thin-film switching memory composite element is manufactured, and the protective film of a fluororesin 5 is formed on the surface of the element, thus realizing the excellent organic thin-film switching-memory composite element stably conducting element operation in atmospheric air COPYRIGHT: (C)1996,JPO

Properties of junctions of crystalline networks of complex TCNQ salts in polymer matrix with silicon

Abstract: The properties of junctions formed by conductive organic polymer composites with networks of two complex tetracyanoquinodimethane (TCNQ) salts (of N-n-butyl-isoquinolinium and of diethyl methyl sulphonium cations) with silicon were studied. We show that it is possible to prepare junctions with quite good rectifying properties, comparable to those using other organic semiconductors. The observed current-voltage characteristics can be satisfactorily fitted using the modified Schottky equation. C-V characteristics show that the transport mechanism, especially in the case of p-Si junctions is more complicated and probably tunnelling between localized levels plays an important role.

Linear and Nonlinear Optical Properties of Polymer Waveguides

Abstract: Experimental evidence that organic semiconductors show some of the highest figures of merit among all the nonlinear optical materials of χ(3) type has increased the interest in these materials during the last few years1. Due to charge conjugation along the polymer backbone or to the presence of side chains constituted of organic molecules with high hyperpolarizabilities, the third order nonlinear response can be strongly enhanced.

Nonlinear Electrophysical Properties of Thin Films of Dibenzotetraazaannulenelapplication of Percolation Model

Abstract: The results obtained demonstrate the appll-caointy of nonlinear percolation theory for the description of charge-transfer processes In thin films of organic semiconductors, with the model object being a polycrystal with a system of Intercrystalllne barriers with large dispersion In heights. It was shown that the appearance of non-linear phenomena In electrophyslcal properties of such samples (long-time current relaxations, nonlinear VAC) Is caused by changing of barrier heights distribution under the Influence of external electric field on the filling of structural (defects) or Impurity (adsorbed O2) states.

A New Type of Organic Semiconductor

Abstract: As one of the new type of organic semiconductors, we report the physico-chemical properties of BTQBT [(bis (1,2,5-thiadiazolo) -p-quinobis (1,3-dithiole)]; the electrical conduction, the ionization energy and the angle-resolved photoemission spectra.

Solid-State Oxygen and Hydrogen Sensing Devices Based on Copper Dicyanoanthraquinone Diimines

Abstract: Substituted dicyanoanthraqumone diimines (DCNAQI) and their related copper complexes, Cu(DCNAQI), have been synthesized and characterized. Most Cu(DCNAQI) complexes possess an activation energy 80–400 meV and strongly absorb in the IR range. Electrochemical investigations with polycrystailine electrodes as thin films reveal that Cu(DCNAQI) behaves as an n-type semiconductor. Under bandgap excitation (4000 cm−1), the photoconductance measured with these Cu(DCNAQI) electrodes was greatly promoted under nitrogen, but very sensitive to O2 or H2. When the conductance difference, Δσ/σdark = (σlight - σ dark)σ dark, was plotted vs the partial pressure of the target molecule, a nearly linear relationship was observed. Among Cu(DCNAQI), Cu(β-methyl-DCNAQI) gave the greatest senstivity for detection of hydrogen, but Cu(α,α′-dichloro-DCNAQI) appeared most sensitive toward oxygen. This remarkable relationship is likely due to retardation of the mobility of electron or hole by interaction with oxygen or hydrogen at the Cu(DCNAQI) electrode surface; a solid-state oxygen/hydrogen sensing device based on these organic semiconductors is proposed.

Physics and applications of low-dimensional organic thin-film transistors

Abstract: We describe the electrical characteristics of thin film transistors with active layers made with /spl alpha/-hexathienylene. The on-conductance in these transistors is two-dimensional. The mobility of field induced carriers and the shape of the current-voltage characteristics depend on the channel length. With interdigitated source-drain regions we have achieved on/off ratios of more than 10/sup 5/. >