We report the first organic light-emitting field-effect transistor. The device structure comprises interdigitated gold source and drain electrodes on a Si/SiO(2) substrate. A polycrystalline tetracene thin film is vacuum sublimated on the substrate forming the active layer of the device. Both holes and electrons are injected from the gold contacts into this layer leading to electroluminescence from the tetracene. The output characteristics, transfer characteristics, and the optical emission properties of the device are reported. A possible mechanism for electron injection is suggested.
In this study, the optical properties of nanocrystalline europium doped yttria, Y2O3:Eu3+ were investigated in dependence on different caging hosts such as porous MCM-41, porous silica, and porous alumina with pore sizes ranging between 2.7 to 80 nm. These results were compared to nanopowders measured in air and aqueous solution whose particle sizes were 5 nm and 8 nm, respectively. All these results were compared to a commercial lamp phosphor powder with a grain size of about 5 μm. The structural properties of the samples were determined by x-ray diffraction and transmission electron microscopy. Investigated optical properties are the photoluminescence emission spectra, the excitation spectra, the lifetimes, and the quantum efficiencies. A heavy dependence of the charge transfer process on the surrounding will be reported and discussed.
An ambipolar pentacene transistor with top-gold and top-calcium contacts has been realized by utilizing a parallactic shadow mask effect during vapor deposition. The pentacene deposited on top of a silicon dioxide gate insulator is doped by Ca at the pentacene/SiO2 interface in order to compensate electron traps. An equivalent circuit model based on a resistor-capacitor network has been developed to describe the basic electrical properties of the transistor. Shockley-like analytical expressions for the output and transfer characteristic, as well as an analytical expression for the potential and charge-carrier distribution in the channel, are derived under the assumption of a high electron-hole recombination probability. The model has been fitted to our experimental results and yields comparable mobilities for both holes and electrons in the order of 0.1cm2∕Vs. The increasing threshold voltages, with an increase in gate voltage, are discussed as an indication for trapped charge carriers within the insulator (SiO2).
A detailed approach to the complex hopping transport in organic semiconductors is presented and used to describe experimental data from Maennig et al. [Phys. Rev. B 64, 195208 (2001)] on the effect of doping on conductivity, mobility and thermopower. In this approach, the energetic distribution of the charge carriers in a Gaussian shaped density of states (DOS) is calculated under thermal equilibrium conditions and compared to the energetic distribution of the current. The description is based on the Miller–Abraham model for hopping in a disordered material and utilizes the so-called transport energy concept. To include also the case of higher electron concentrations in the tail states of the DOS the Fermi distribution was taken into account. Furthermore, additional trap states in the gap are considered to describe the experimental data at low doping concentration more correctly. In the framework of the model there is no indication of a thermally activated ionization of the dopants. In contrast to other descriptions, the position of the Fermi energy and transport energy are calculated from the model. It is demonstrated that the principal behavior of the transport parameter can be well explained in terms of classical semiconductor physics.
Control over spatial positioning of CdSe quantum dots(QDs) is a very important criterion for device fabrication. These authors utilize the ordered array of pores provided by the mesoporous material MCM‐41 to achieve this. TEM of a single CdSe@MCM‐41 particle (see Figure) shows that the hexagonally ordered mesostructure of MCM‐41 is still intact after the growth of CdSe nanoparticles inside the mesopores.
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