Organic semiconductors, ii- properties, synthesis, and application
Organic semiconductors - conductivity and semiconductivity, photo conductivity, excited states, and dielectric effects
SEMICONDUCTOR↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Conduction mechanism in organic semiconductors
Charge carrier mobility in organic semiconductors, described using molecular orbital theory
MOLECULAR ORBIT↗
Studies on organic semiconductors. 15: Effects of the substituents on the photoconductivities of substituted anthracenes
The photocurrents of the substituted anthracenes, 1,5-diacetylanthracene (2), 1-acetylanthracene (3), 9-acetylanthracene (4), 1,5-dichloroanthracene (5), 1,5-diethylanthracene (6), 1,5-dimethoxyanthracene (7), 9-cyanoanthracene (8), and anthracene (1) were measured by using their surface type cells in nitrogen. The compounds of (1), (5), (6), (7), and (8) showed the photocurrent spectra which corresponded to the absorption spectra of their evaporated films. In the cases of (2) and (3), however, the anomalous photocurrent appeared in the threshold region of their absorption spectra. The appearance of the anomalous photocurrent was characteristic of anthracenes having the acetyl group at 1- and/or 5-position. The magnitude of the photocurrents of the 1,5-disubstituted anthracenes was similar to that of (1). The photocurrents of the monosubstituted anthracenes were smaller than that of (1). Among the monosubstituted anthracenes, the compound (4) showed no photocurrent under the same conditions. Contrary to the results obtained in the cases of phenazines, the photoconductivities of the anthracene derivatives became better in air.
Sugimoto, A.↗
The effect of surface conditions on the work function of insulators and semiconductors
Ionization energies of organic semiconductors were determined using single crystals of the material. The theory of the method is essentially that of Millikan's oil drop experiment. The technique employed in the experiment is based on the electrostatic method of balancing a charged particle in an electric field against the force of gravity for different excitation energies above the threshold value, and from an estimate of the balancing voltages, read off the ionization energy from the intercept of the energy axis in a plot wavelength corresponding to the balancing potential for the incident radiation of wavelength. In the modified technique which is adopted in the present experimental investigation, a small single crystal is suspended by a fine quartz fiber between two vertical capacitor plates to which a suitable high voltage is applied.
George, A.↗
Wholly Aromatic Ether-Imides as n-Type Semiconductors
Some wholly aromatic ether-imides consisting of rod-shaped, relatively-low-mass molecules that can form liquid crystals have been investigated for potential utility as electron-donor-type (ntype) organic semiconductors. It is envisioned that after further research to improve understanding of their physical and chemical properties, compounds of this type would be used to make thin film semiconductor devices (e.g., photovoltaic cells and field-effect transistors) on flexible electronic-circuit substrates. This investigation was inspired by several prior developments: Poly(ether-imides) [PEIs] are a class of engineering plastics that have been used extensively in the form of films in a variety of electronic applications, including insulating layers, circuit boards, and low-permittivity coatings. Wholly aromatic PEIs containing naphthalene and perylene moieties have been shown to be useful as electrochromic polymers. More recently, low-molecular-weight imides comprising naphthalene-based molecules with terminal fluorinated tails were shown to be useful as n-type organic semiconductors in such devices as field-effect transistors and Schottky diodes. Poly(etherimide)s as structural resins have been extensively investigated at NASA Langley Research Center for over 30 years. More recently, the need for multi-functional materials has become increasingly important. This n-type semiconductor illustrates the scope of current work towards new families of PEIs that not only can be used as structural resins for carbon-fiber reinforced composites, but also can function as sensors. Such a multi-functional material would permit so-called in-situ health monitoring of composite structures during service. The work presented here demonstrates that parts of the PEI backbone can be used as an n-type semiconductor with such materials being sensitive to damage, temperature, stress, and pressure. In the near future, multi-functional or "smart" composite structures are envisioned to be able to communicate such important parameters to the flight crew and provide vital information with respect to the operational status of their aircraft.
Weiser, Erik↗
An electrostatic suspension method for determining photoionization energies of solids.
A sample is suspended on a quartz fibre in an electrostatic condenser and the onset of ionization with photon energy is determined through the potential required to restore zero deflection. Results for a few organic semiconductors are given.
George, A.↗
Photoacoustic spectroscopy of condensed matter
Photoacoustic spectroscopy is a new analytical tool that provides a simple nondestructive technique for obtaining information about the electronic absorption spectrum of samples such as powders, semisolids, gels, and liquids. It can also be applied to samples which cannot be examined by conventional optical methods. Numerous applications of this technique in the field of inorganic and organic semiconductors, biology, and catalysis have been described. Among the advantages of photoacoustic spectroscopy, the signal is almost insensitive to light scattering by the sample and information can be obtained about nonradiative deactivation processes. Signal saturation, which can modify the intensity of individual absorption bands in special cases, is a drawback of the method.
Somoano, R. B.↗
Solar cells of metal-free phthalocyanine dispersed in polyvinyl carbazole. 1: Effects of the recrystallization of H2PC on cell characteristics
The development of an organic semiconductor solar cell and the effects of the recrystallization of metal free phthalocyanine (H2PC) on the characteristics of NESA/H2PC-PVK/Au sandwich cells were investigated. Alfa-H2PC sandwich cells showed photovoltage and photocurrent in a two direction opposite to that shown y as supplied H2PC cells, which consists mainly of beta-H2PC. Some difference was observed in the response times of the two cells. It is suggested that photocharacteristics change with the specific resistance of the H2PC, which is related to its crystal forms. In the cells with low resistance H2PC carriers are generated in H2PC by illumination, while in high resistance H2PC cells, carriers are generated in PVK which is sensitized with H2PC.
Shimura, M.↗
International Conference on Vacuum Ultraviolet Radiation Physics, 8th, Lunds Universitet, Sweden, Aug. 4-8, 1986, Proceedings
The interactions of VUV radiation with solids are explored in reviews and reports of recent theoretical and experimental investigations from the fields of atomic and molecular physics, solid-state physics, and VUV instrumentation. Topics examined include photoabsorption and photoionization, multiphoton processes, plasma physics, VUV lasers, time-resolved spectroscopy, synchrotron radiation centers, solid-state spectroscopy, and dynamical processes involving localized levels. Consideration is given to the fundamental principles of photoemission, spin-polarized photoemission, inverse photoemission, semiconductors, organic materials, and adsorbates.
Nilsson, Per-Olof↗
Heteroepitaxial growth of 3-5 semiconductor compounds by metal-organic chemical vapor deposition for device applications
The purpose of this research is to design, install and operate a metal-organic chemical vapor deposition system which is to be used for the epitaxial growth of 3-5 semiconductor binary compounds, and ternary and quaternary alloys. The long-term goal is to utilize this vapor phase deposition in conjunction with existing current controlled liquid phase epitaxy facilities to perform hybrid growth sequences for fabricating integrated optoelectronic devices.
Collis, Ward J.↗
Innovations in microelectronics and solid state at North Carolina Agricultural and Technical State University
Research in the following areas is described: (1) Characterization and applications of metallic oxide devices; (2) Electronic properties and energy conversion in organic amorphous semiconductors; (3) Material growth and characterization directed toward improving 3-5 heterojunction solar cells.
Williams, L., Jr.↗
Improving engineering effectiveness
Methodologies to improve engineering productivity were investigated. The rocky road to improving engineering effectiveness is reviewed utilizing a specific semiconductor engineering organization as a case study. The organization had a performance problem regarding new product introductions. With the help of this consultant as a change agent the engineering team used a systems approach to through variables that were effecting their output significantly. Critical factors for improving this engineering organization's effectiveness and the roles/responsibilities of management, the individual engineers and the internal consultant are discussed.
Fiero, J. D.↗
High-performance field effect transistors with self-assembled nanodielectrics
Field effect transistor devices comprising III-V semiconductors and organic gate dielectric materials, such dielectric materials as can afford flexibility in device design and fabrication.
Marks, Tobin J.↗
Ellipsometric study of metal-organic chemically vapor deposited III-V semiconductor structures
An ellipsometric study of MOCVD-grown layers of AlGaAs and InGaAs in thick films and strained layer complex structures is presented. It is concluded that the ternary composition of thick nonstrained layers can be accurately determined to within experimental errors using numerical algorithms. In the case of complex structures, thickness of all layers and the alloy composition of nonstrained layers can be determined simultaneously, provided that the correlations between parameters is no higher than 0.9.
Alterovitz, Samuel A.↗
Growing Organic Crystals By The Czochralski Method
Apparatus grows high-quality single crystals of organic compounds by Czochralski method. In Czochralski process, growing crystal lifted from middle of molten material without touching walls. Because of low melting temperatures of organic crystals, glass vessels usable. Traditional method for inorganic semiconductors adapted to optically nonlinear organic materials.
Shields, Angela↗
Photoreflectance for in-situ characterization of MOCVD growth of semiconductors under micro-gravity conditions
A contactless electromodulation technique of photoreflectance (PR) was developed for in-situ monitoring of metal-organic chemical vapor deposition (MOCVD) semiconductor growth for micro-gravity applications. PR can be employed in a real MOCVD reactor including rotating substrate (approximately 500 rev/min) in flowing gases and through a diffuser plate. Measurements on GaAs and Ga(0.82)Al(0.18)As were made up to 690 C. The direct band gaps of In(x)Ga(1-x)As (x = 0.07 and 0.16) were evaluated up to 600 C. In order to address the question of real time measurement, the spectra of the direct gap of GaAs at 650 C was obtained in 30 seconds and 15 seconds seems feasible.
Pollak, Fred H.↗
The Mars oxidant experiment (MOx) for Mars '96
The MOx instrument was developed to characterize the reactive nature of the martian soil. The objectives of MOx were: (1) to measure the rate of degradation of organics in the martian environment; (2) to determine if the reactions seen by the Viking biology experiments were caused by a soil oxidant and measure the reactivity of the soil and atmosphere: (3) to monitor the degradation, when exposed to the martian environment, of materials of potential use in future missions; and, finally, (4) to develop technologies and approaches that can be part of future soil analysis instrumentation. The basic approach taken in the MOx instrument was to place a variety of materials composed as thin films in contact with the soil and monitor the physical and chemical changes that result. The optical reflectance of the thin films was the primary sensing-mode. Thin films of organic materials, metals, and semiconductors were prepared. Laboratory simulations demonstrated the response of thin films to active oxidants.
Flight Experiment↗
Reed Solomon codes for error control in byte organized computer memory systems
A problem in designing semiconductor memories is to provide some measure of error control without requiring excessive coding overhead or decoding time. In LSI and VLSI technology, memories are often organized on a multiple bit (or byte) per chip basis. For example, some 256K-bit DRAM's are organized in 32Kx8 bit-bytes. Byte oriented codes such as Reed Solomon (RS) codes can provide efficient low overhead error control for such memories. However, the standard iterative algorithm for decoding RS codes is too slow for these applications. Some special decoding techniques for extended single-and-double-error-correcting RS codes which are capable of high speed operation are presented. These techniques are designed to find the error locations and the error values directly from the syndrome without having to use the iterative algorithm to find the error locator polynomial.
Lin, S.↗