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Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 25: Organic films II

O 25.11: Talk

Tuesday, March 28, 2006, 18:15–18:30, PHY C213

In-situ electrical investigations of the growth of dihexyl-oligothiophenes in organic field effect transistors — •Torsten Balster, Tobias Muck, Arne Hoppe, Jörg Seekamp, and Veit Wagner — International University Bremen, Bremen, Germany

Optimized contact properties are essential for applications of thin film organic field effect transistors (OFET) enabling higher current level and switching frequencies. We have grown thin films of dihexyl-oligothiophene with 4 to 7 thiophene rings (DHnT) on Ti/Au bottom contact transistor templates in ultrahigh vacuum, because the energetic difference between the HOMO and the Fermi energy of the Au contact is varied by the number of chromophores in oligothiophenes. The channel width of the transistors ranges from 100 down to 5 µm.
The in-situ electrically characterized samples of these thiophene derivatives demonstrates oscillatory behaviour of the charge carrier mobilities during growth indicating layer-by-layer mode. The onset of the current could be found in excess of 2/3 of a monolayer, whereas saturation after more than 2 monolayers is observed. Furthermore, higher mobilities (up to 10−1Vs/cm2 for DH7T) could be found for increasing number of thiophene rings at optimized growth temperatures (190C) of the sample.
The voltage drops at the source and drain electrode are independently determined by means of 4-point measurements using additional, screened electrodes within the organic channel showing a major drop up to 1 V for DH6T at the source electrode.

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