Prepare with Care: Low Contact Resistance of Pentacene Field-Effect Transistors with Clean and Oxidized Gold Electrodes – Publication by A2 (Witte)

In a new publication in Organic Electronics, project A2 (Witte) reports on the establishment of a complete high vacuum-based manufacturing and electronic characterization of organic field effect transistors (OFET).

A4 OFET 2021

Photograph and force microscopy image of the vacuum-processed OFETs, which enables their electrical characterization without exposing the devices to air (Image: Y. Radiev).

The electronic coupling between OSC and metallic electrodes is of key importance for the efficiency of charge carrier injection in organic electronic devices, such as OFETs or photovoltaic cells, as it determines their idle power. Surface science-based model studies have mainly focused on the energy level alignment at such metal-organic interfaces without measuring real contact resistances, while device studies are typically performed without any microscopic structural and electronic interface characterization. In the present work, the authors introduced a high vacuum-based manufacturing of bottom contact OFETs that enables cleaning and controlled modification of metal contacts before the organic film deposition. This approach not only excludes any exposure to air, it also allows to examine the influence of controlled exposure to air on the device characteristics.

Using the example of the prototypical OSC pentacene it is demonstrated that FET structures with thoroughly cleaned gold electrodes reveal a remarkably low contact resistance. This can be further improved if the electrodes are O2 plasma treated before the pentacene film growth, which results in a thin gold oxide layer and yields one of the lowest contact resistances ever reported for this system. It is shown that this not only causes an improved energy level alignment at the metal-organic interface but also suppresses a pronounced dewetting. In addition, it was demonstrated that controlled exposure to air – even for a short time – significantly affects the device performance.

The present study is an important milestone as it enables detailed electronic transport measurements through metal-OSC interfaces with poly- and single crystal organic semiconductors. This work paves the way for a knowledge transfer about the properties of idealized model interfaces to real electronic devices applications.

Publication                                     

Yurii Radiev, Felix Widdascheck, Michael Göbel, Alrun Aline Hauke and Gregor Witte,
Prepare with Care: Low Contact Resistance of Pentacene Field-Effect Transistors with Clean and Oxidized Gold Electrodes
Org. Electron. 89 (2021) 106030 DOI:10.1016/j.orgel.2020.106030

Contact

Prof. Dr. Gregor Witte
Philipps-Universität Marburg
SFB 1083, project A2
Tel.: 06421 28-21384
EMAIL

Prof. Dr. F.S. Tautz won a price at „Falling Walls – The World Science Summit“

At „Falling Walls – The World Science Summit“ during the Berlin Science Week, Prof. Dr. F.S. Tautz, PI of SFB project A12 (Tautz/Bocquet/Kumpf), was declared the winner in the category „Engineering and Technology“ with his contribution „Breakting the Wall of Building with Molecules“.

Tautz Portait

„Falling Walls“ is an event that brings together some of the best researchers of the world, discussing and celebrating the latest breakthroughs in science and society since over 10 years. The breakthroughs represent significant advances, groundbreaking developments and innovative ideas stretching over ten different categories.

 

Falling Walls

Falling Walls 2020 during the Berlin Science Week

Prof. Tautz (SFB project A12) submitted his 5-min long nomination film (link see below) in the category “Engineering and Technology” titled “Breaking the Wall of Building with Molecules”. In this video, Prof. Tautz gives a short insight into his research. Although manipulating atoms on surfaces is already performed for several years, researchers are struggling with moving and arranging molecules. He explains how an artificial intelligence was trained by reinforcement learning in reality and in model systems at the same time. Consequently, the agent got highly adaptive and become able to successfully manipulate molecules.

With this technique, targeted fabrication of molecular machines can be achieved giving rise to new promising technologies with high-level functionalities. Winning this price is not only a great honor for Prof. Tautz, but also represents the high importance and appreciation of the SFB’s research.

For further details, see the nomination film.

 

Contact

Prof. Dr. Stefan Tautz
FZ Jülich, SFB project A12
PGI, Experimental Physics
Tel.: +49 (0)2461 61-4561
EMAIL

Super-resolution lightwave tomography of electronic bands in quantum materials – Publication by B4

The researchers developed a method, which was published in Science, to reconstruct the band structure of quantum materials with very high precision

Science B4

A light flash (yellow) induces the movement of electrons in the band structure (red curve) resulting in the formation of localized electronic interference combs (peaks). The emitted radiation (red) enables the analysis of the electronic band structure. © Markus Borsch, University of Michigan, USA

Stacking of two-dimensional (2D) materials yield promising properties for the development of new devices with outstanding functionality. However, detailed knowledge of the electronic structure is necessary to tailor their properties. Within the cooperation of Prof. Huber (Uni Regensburg), Prof. Kira (Uni Michigan) and Prof. Koch (Uni Marburg, project B4), a new method was developed enabling the reconstruction of the band structure of 2D materials.

The quantum material WSe2 was simultaneously excited by two laser pulses in the visible range and in the THz spectral range. The resonant excitation of the weak optical pulse and simultaneous irradiation with a strong THz pulse result in harmonic sideband generation (HSG) in the transmitted spectrum. Due to the wave-particle dualism of electrons, electronic interference combs evolve in momentum space (cf. Figure on the left). By analyzing multiple sideband spectra at different THz frequencies and intensities, it is possible to reconstruct the band structure with super-resolution.

This concept offers an all-optical and practical approach for a three-dimensional tomography of the electronic structure of small quantum materials as shown for WSe2. This work is a great extend to the research in the SFB as it provides the possibility to examine the electronic band structure of 2D materials, such as TMDCs, even under ambient conditions.

Publication

M. Borsch, C.P. Schmid, L. Weigl, S. Schlauderer, N. Hofmann, C. Lange, J.T. Steiner, S.W. Koch, R. Huber, M. Kira
Super-resolution lightwave tomography of electronic bands in quantum materials
Science 370 (2020) 1204 DOI:10.1126/science.abe2112

Contact

Prof. Dr. Stephan W. Koch
Philipps-Universität Marburg
Department of Physics, Theoretical Semiconductor Physics
Renthof 5, 35032 Marburg
Tel.: 06421 28-21336
EMAIL