Dresden 2006 – wissenschaftliches Programm
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O: Oberflächenphysik
O 25: Organic films II
O 25.11: Vortrag
Dienstag, 28. März 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 (190∘C) 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.