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- Determination of deep and shallow levels in conjugated polymers by electrical methodsPublication . Stallinga, Peter; Gomes, Henrique L.; Rost, H.; Holmes, A. B.; Harrison, M. G.; Friend, R. H.; Biscarini, F.; Taliani, C.; Jones, G. W.; Taylor, D. M.Conjugated organic semiconductors have been submitted to various electrical measurement techniques in order to reveal information about shallow levels and deep traps in the forbidden gap. The materials consisted of poly[2-methoxy, 5 ethyl (2' hexyloxy) paraphenylenevinylene] (MEH-PPV), poly(3-methylthiophene) (PMeT), and alpha-sexithienyl (alpha T6) and the employed techniques were IV, CV, admittance spectroscopy, TSC, capacitance and current transients. (C) 1999 Elsevier Science B.V. All rights reserved.
- Influence of the metal center on the morphology of coordination compounds thin filmsPublication . Toffolo, F.; Brinkmann, M.; Greco, O.; Biscarini, F.; Taliani, C.; Gomes, Henrique L.; Aiello, I.; Ghedini, M.Thin film morphology of tris-(8-hydroxyquinolate) aluminium (III) (Alq3) and bis-(8-hydroxyquinolate) oxovanadium (IV) (VOq2) are compared. Alq3 films deposited onto mica at 300K look almost featureless, but dendrimers or randomly distributed needle-shaped crystallites appear as a consequence of crystallization in time. We show that a possible origin of this process is exposure to solvent vapors. On the other hand, VOq2 films retain their textured morphology as thickness increases because of stabilizing intermolecular interactions between vanadyl groups.
- Electrical characterization of organic based transistors: stability issuesPublication . Gomes, Henrique L.; Stallinga, Peter; Dinelli, F.; Murgia, M.; Biscarini, F.; De Leeuw, D. M.; Muccini, M.; Mullen, K.An investigation into the stability of metal insulator semiconductor (MIS) transistors based on alpha-sexithiophene is reported. In particular the kinetics of the threshold voltage shift upon application of a gate bias has been determined. The kinetics follow a stretched-hyperbola type behavior, in agreement with the formalism developed to explain metastability in amorphous-silicon thin film transistors. Using this model, quantification of device stability is possible. Temperature-dependent measurements show that there are two processes involved in the threshold voltage shift, one occurring at T approximate to 220 K and the other at T approximate to 300 K. The latter process is found to be sample dependent. This suggests a relation between device stability and alpha-sexithiophene deposition parameters. Copyright (c) 2005 John Wiley A Sons, Ltd.
- Electrical instabilities in organic semiconductors caused by trapped supercooled waterPublication . Gomes, Henrique L.; Stallinga, Peter; Colle, M.; De Leeuw, D. M.; Biscarini, F.It is reported that the electrical instability known as bias stress is caused by the presence of trapped water in the organic layer. Experimental evidence as provided by the observation of an anomaly occurring systematically at around 200 K. This anomaly is observed in a variety of materials, independent of the deposition techniques and remarkably coincides with a known phase transition of supercooled water. Confined water does not crystallize at 273 K but forms a metastable liquid. This metastable water behaves electrically as a charge trap, which causes the instability. Below 200 K the water finally solidifies and the electrical traps disappear. (c) 2006 American Institute of Physics.
- Electronic transport in field-effect transistors of sexithiophenePublication . Stallinga, Peter; Gomes, Henrique L.; Biscarini, F.; Murgia, M.; De Leeuw, D. M.The electronic conduction of thin-film field-effect-transistors (FETs) of sexithiophene was studied. In most cases the transfer curves deviate from standard FET theory; they are not linear, but follow a power law instead. These results are compared to conduction models of "variable-range hopping" and "multi-trap-and-release". The accompanying IV curves follow a Poole-Frenkel (exponential) dependence on the drain voltage. The results are explained assuming a huge density of traps. Below 200 K, the activation energy for conduction was found to be ca. 0.17 eV. The activation energies of the mobility follow the Meyer-Neldel rule. A sharp transition is seen in the behavior of the devices at around 200 K. The difference in behavior of a micro-FET and a submicron FET is shown. (C) 2004 American Institute of Physics.
- Bias-induced threshold voltages shifts in thin-film organic transistorsPublication . Gomes, Henrique L.; Stallinga, Peter; Dinelli, F.; Murgia, M.; Biscarini, F.; De Leeuw, D. M.; Muck, T.; Geurts, J.; Molenkamp, L. W.; Wagner, V.An investigation into the stability of metal-insulator-semiconductor (MIS) transistors based on alpha-sexithiophene is reported. In particular, the kinetics of the threshold voltage shift upon application of a gate bias has been determined. The kinetics follow stretched-hyperbola-type behavior, in agreement with the formalism developed to explain metastability in amorphous-silicon thin-film transistors. Using this model, quantification of device stability is possible. Temperature-dependent measurements show that there are two processes involved in the threshold voltage shift, one occurring at Tapproximate to220 K and the other at Tapproximate to300 K. The latter process is found to be sample dependent. This suggests a relation between device stability and processing parameters. (C) 2004 American Institute of Physics.
- The effect of water related traps on the reliability of organic based transistorsPublication . Gomes, Henrique L.; Stallinga, Peter; Colle, M.; Biscarini, F.; De Leeuw, D. M.The electrical stability of metal-insulator semiconductor (MIS) capacitors and field-effect transistor structures based in organic semiconductors were investigated. The device characteristics were studied using steady state measurements AC admittance measurements as well as techniques for addressing trap states. Temperature-dependent measurements show clear evidence that an electrical instability occurs above 200 K and is caused by an electronic trapping process. Experimental results show that water is responsible for the trapping mechanism. (c) 2006 Elsevier B.V. All rights reserved.