Publications on the project |
001 Dependence of Meyer-Neldel Energy on Energetic Disorder in Organic Field Effect Transistors |
Authors: | Mujeeb Ullah, I.I. Fishchuk, A. Kadashchuk, P. Stadler, A. Pivrikas, C. Simbruner, V. N. Poroshin, N. S. Sariciftci and H.Sitter | |
Summary: | Meyer–Neldel rule for charge carrier mobility was studied in C60-based organic field effect
transistors _OFETs_ fabricated at different growth conditions which changed the degree of disorder in the films. The energetic disorder in the films was found to correlate with a shift in the Meyer–Neldel energy, which is in excellent agreement with the predictions of a hopping-transport model for the temperature dependent OFET mobility in organic semiconductors with a Gaussian density-of-states _DOS_. Using this model the width of the DOS was evaluated and it was found to decrease from 88 meV for the films grown at room temperature to 54 meV for films grown at
250 °C.
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Edition: | Appl. Phys. Lett., 96 | | | 2010,
213306-213313,English |
001 Electric field dependence of charge-carrier hopping transport within the random energy landscape in an organic field effect transistor |
Authors: | I. I. Fishchuk, A. Kadashchuk, Mujeeb Ullah, H. Sitter, A. Pivrikas, J. Genoe and H. Bässler | |
Summary: | We extended our analytical effective medium theory [Phys. Rev. B 81, 045202 (2010)] to describe the temperature-dependent hopping charge carrier mobility at arbitrary electric fields in the large carrier density regime. Special emphasis was made to analyze the influence of the lateral electric field on the Meyer–Neldel (MN) phenomenon observed when studying the charge mobilities in thin-film organic field-effect transistors (OFET).Our calculations are based on the average hopping transition time approach, generalized for large carrier concentration limit finite fields, and taking into account also spatial energy correlations. The calculated electric field dependences of the hopping mobility at large carrier concentrations are in good agreement with previous computer simulations data. The shift of the MN temperature in an OFET upon applied electric field is shown to be a consequence of the spatial energy correlation in the organic semiconductor film. Our calculations show that the phenomenological Gill equation is clearly inappropriate for describing conventional charge carrier transport at low carrier concentrations. On the other hand a Gill-type behavior has been observed in a temperature range relevantformeasurementsofthechargecarriermobilityinOFETstructures.Sincethepresentmodelisnotlimited to zero-field mobility, it allows a more accurate evaluation of important material parameters from experimental data measured at a given electric field. In particular, we showed that both the MN and Gill temperature can be used for estimating the width of the density of states distribution. | |
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Edition: | Phys. Rev. B., 86 | | | 2012,
045207-045212,English |
001 Photosensitivity of top gate C60 based OFETs: Potential applications for high efficiency organic photodetector |
Authors: | . R. Ahmed, A. Kadashchuk, C. Simbrunner, G. Schwabegger, M. Havlicek, E. Głowacki, N. S. Sariciftci, M. A. Baig, and H. Sitter | |
Summary: | The comparison of light-induced effects in bottom-gate and top-gate organic field effect transistors (OFETs) provide a clear indication, that the nature of interface between the active layer and the gate dielectric plays a major role in the observed light-induced threshold voltage shift. The nature of interface was also analyzed by electron spin resonance (ESR) experiments, which provides a direct evidence for the creation of free radical species when parylene is deposited on the top of the C60 semiconductor layer. The rate of change of light-induced threshold voltage shift strongly depends on the wavelength and intensity of the incident light, and transverse electric field at the interface. The observed effects provide a strong base for the realization of high efficiency organic photodetectors and optical memory devices. The responsivity of organic photodetector was measured up to 1047 A/W. | |
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Edition: | Org. Electr., 15, Issue 1 | | | 2014,
175 -181 ,English |
001 Electric field and grain size dependence of Meyer-Neldel energy in C60 films |
Authors: | M.Ullah, A. Pivrikas, I. I. Fishchuk, A. Kadashchuk, P. Stadler, C. Simbrunner, N. S. Sariciftci, and H. Sitter | |
Summary: | Meyer–Neldel rule for charge carrier mobility measured in C60-based organic field-effect transistors (OFETs) at different applied source drain voltages and at different morphologies of semiconducting fullerene films was systematically studied. A decrease in the Meyer–Neldel energy EMN from 36 meV to 32 meV was observed with changing electric field in the channel. Concomitantly a decrease from 34 meV to 21 meV was observed too by increasing the grain size and the crystallinity of the active C60 layer in the device. These empiric findings are in agreement with the hopping-transport model for the temperaturedependent charge carrier mobility in organic semiconductors with a Gaussian density of states (DOS). Experimental results along with theoretical descriptions are presented. | |
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Edition: | Synth. Met., 161, | | | 2011,
1987 -1990 ,English |
The events in the framework of the project |
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001 Executant:Institute of Physics, Department of Physics and Astronomy, Section Physical, Engineering and Mathematics 1.1. Nanophysics: fundamental problems Purpose:The Goal of the project is investigation of features of the physical processes in the nanoscale objects of different nature – carbon nanotubes, nanoparticles and nano-layers of metals, semiconductors and insulators which are placed on surfaces or surrounded by different media: insulators, non-organic and organic semiconductors. The various physical properties of these systems will be studied: optical, electric, absorption, magnetic, transport, luminescent. Expected results:Issue of new types of products: methods, theories Stage 1:Investigation of the filamentation phenomenon of the femtosecond radiation in transparent matrices and composites based on the nanoparticles of metals, semiconductors, new allotropic carbon forms. Studies of the laser properties of the 1D, 2D photonic crystals. Stage 2:Investigation of influence of irradiation by the 1 MeV electrons and the 60Co gamma-quanta on the electric conductivity of the carbon nanotubes. Investigation of the lateral electric transport and hot electron radiation in the structures with the single quantum wells and different kind of doping by shallow impurity. Stage 3:Investigation of the electric and magneto-transport in the nano-dimensional structures of different nature. Stage 4:Investigation of the optical and non-linear optical properties of the metallic and semiconductor particles and clusters with the nanometer dimensions. Stage 5:Optical mechanics of the nanoparticles, nano-colloids, atomic and molecular clusters, atomic systems.
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