Examination of Au, Cu, and Al contacts in organic field-effect transistors via displacement current measurements

Yan Liang, Hsiu Chuang Chang, P. Paul Ruden, C. Daniel Frisbie

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28 Scopus citations


Displacement current measurements (DCM) on long-channel capacitors (LCCs) were used to examine carrier injection and extraction processes in organic field-effect transistors (OFETs). An LCC can be seen as an OFET with one channel contact removed and the conducting channel elongated to millimeter range. While carrier injection and extraction processes occur simultaneously in OFETs during traditional DC measurements, these two processes can be examined separately with LCCs and DCMs. In addition, the numbers of injected, extracted, and trapped carriers can be determined by integrating the displacement current with respect to time. Pentacene LCCs with Au, Cu, and Al contacts were fabricated. Surprisingly, it was found that more carriers were trapped in the Au devices than in the Cu devices even though the pentacene film and dielectric layers were essentially identical. We propose that carrier trapping in the long channel of the Au devices is indirectly caused by the deep trap states at the pentacene-dielectric interface in the contact region generated by Au penetration. In addition, ambipolar injection and transport were observed in an LCC with an Al contact and a PMMA buffer layer between pentacene and SiO 2.

Original languageEnglish (US)
Article number064514
JournalJournal of Applied Physics
Issue number6
StatePublished - Sep 15 2011

Bibliographical note

Funding Information:
This work was partially supported by the MRSEC Program of the National Science Foundation under Award Number DMR-0819885. Additional support was provided by the Department of Energy, Basic Energy Sciences. Access to the facilities of the Minnesota Supercomputing Institute for Advanced Computational Research is gratefully acknowledged. YL thanks Salil Bapat for help with preparing ambipolar devices.


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