Anisotropic Strain Effect on Electron Transport in C 60 Organic Field Effect transistors
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Anisotropic Strain Effect on Electron Transport in C60 Organic Field Effect transistors Akash Nigam,1,2,3*, Günther Schwabegger,4, Mujeeb Ullah,4, Rizwan Ahmed,4,5, Ivan I. Fishchuk,6, Andrey Kadashchuk,6,7, Clemens Simbrunner,4, Helmut Sitter,4, Malin Premaratne,1,2, and V.Ramgopal Rao,1,3 1
IITB-Monash Research Academy, IIT Bombay, Mumbai 400076, India Department of Electrical and Computer Systems Engineering, Monash University, Clayton, Victoria 3800, Australia 3 Department of Electrical Engineering, Center of Excellence in Nanoelectronics, IIT Bombay, Mumbai, 400076, India 4 Institute of Semiconductor and Solid State Physics, Johannes Kepler University, A-4040 Linz, Austria 5 National Center for Physics, Quaid-e-Azam University Campus, Islamabad, Pakistan 6 Institute of Physics, National Academy of Sciences of Ukraine, 03028 Kyiv, Ukraine 7 IMEC, Kapeldreef 75, B-3001 Leuven, Belgium Email:[email protected] 2
ABSTRACT Mechanical flexibility is one of the key advantages of organic semiconducting films in applications such as wearable-electronics or flexible displays. The present study is aimed at gaining deeper insight into the effect of strain on charge transport properties of the organic semiconductor films. We have fabricated high performance C60 top gate organic field effect transistors (OFET) on flexible substrates and characterized the devices by curling the substrates in concave and convex manner, to apply varying values of compressive and tensile strain, respectively. Electron mobility is found to increase with compressive strain and decrease with tensile strain. The observed strain effect is found to be strongly anisotropic with respect to the direction of flow of current. This observation on mobility is quantified using an Extended Gaussian Disorder Model (EGDM) for the hopping charge transport. We suggest that the observed strain dependence of the electron transport is dominated by a change in the effective charge hopping distance over the grain boundaries in polycrystalline C60 films. INTRODUCTION Mechanical flexibility is one the key advantages of organic semiconductors [1-3]. Performance reliability of organic devices on rolling, twisting and curling is of utmost importance for the success of niche applications like wearable electronics and large area displays. Curling of flexible substrates has been known to introduce strain in organic devices [2, 4]. Besides the reliability issues associated with strain, the potential use of strain to improve the charge mobility in organic semiconductors (OSC) has also been recently demonstrated by Giri et al [5]. Consequently, it is important to understand the impact of strain on organic semiconductors. In inorganic devices, strain is often used to improve the charge mobility and understand the details
of charge transport [6]. In silicon, the effect of strain on p-type and n-type devices is complementary. Under compressive strain the hole mobility increases in p-doped silicon, whereas the electron mobility decreases for n-type devices and, vice versa for te
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