Electron Irradiation of Graphene Field Effect Transistor Devices
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Electron Irradiation of Graphene Field Effect Transistor Devices Sung Oh Woo1 and Winfried Teizer1, 2 1 Department of Physics and Astronomy, Texas A&M University, College Station, TX 778434242, U.S.A. 2 WPI-Advanced Institute for Materials Research, Tohoku University, Sendai, Japan.
ABSTRACT We report the effects of electron irradiation on graphene Field Effect Transistor (FET) devices. We irradiated the graphene devices with 30keV electrons and measured the electrical transport properties in high vacuum in-situ. Upon electron irradiation, a Raman ‘D’ band appears. In addition, we observed that the doping behavior of the graphene devices changed from P to N type as a result of the irradiation. We also observed a shift of the Dirac point while the graphene FET device stays in vacuum and after it interacted with environmental molecules under ambient conditions.
INTRODUCTION Graphene, a single layer of carbon atoms, has attracted a great amount of attention not only due to scientific interest but also due to potential applications such as high speed electronic devices [1], molecular sensors [2], and molecule storage media [3]. In particular, graphene is considered a potential material for the post silicon era due to its extraordinary electronic properties. Because Scanning Electron Microscopy (SEM) and Electron Beam Lithography (EBL) are important tools in nanofabrication and characterization, Graphene Field Effect Transistor (GFET) devices might be routinely exposed to energetic electron beams. Therefore, it is important to study the effect of electron irradiation on graphene. We present the effects of electron irradiation on graphene FET devices, focusing specifically on its electronic transport properties.
EXPERIMENT Graphene FET devices for electronic transport measurements were fabricated by the mechanical exfoliation technique. Graphene flakes were cleaved from ‘YGA’ grade highly oriented pyrolytic graphite and transferred onto substrates. Consisting of 285nm-think oxide layers grown on silicon wafers, these were selected in order to maximize contrast of the graphene flakes [4]. Single layer graphene flakes were then selected by optical microscopy and confirmed by Raman spectroscopy [5]. The electrodes for electronic transport measurements were patterned by EBL, and Cr(3nm)/Au(50nm) electrodes were deposited by thermal evaporation. The GFET
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molecules. Furthermore, the P-type doping behavior changes to N-type when annealing, which is in agreement with our observations. In this sense, both the vacuum and the annealing processes force some physically adsorbed air molecules or adatoms to desorb from the graphene surface. As a result, it is typically seen that adatoms contribute to the P-type doping behavior of graphene. After the electron irradiation of the graphene, the Raman ‘D’ band, which is measured after transport measurements, appeared, as shown in Figure 2 (b). This is an indication of defect creation. The Raman ‘defect’ signature appears when the symmetry of the A1g mode, a lateral vibration of
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