Effects of Long-Time Current Annealing to the Hysteresis in CVD Graphene on SiO 2
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.366
Effects of Long-Time Current Annealing to the Hysteresis in CVD Graphene on SiO2 U. Kushan Wijewardena, Tharanga Nanayakkara, Rasanga Samaraweera, Sajith Withanage, Annika Kriisa, Ramesh G. Mani Department of Physics & Astronomy, Georgia State University, Atlanta, GA 30303, USA
ABSTRACT
Graphene specimens produced by chemical vapor deposition usually show p-type characteristics and significant hysteresis in ambient conditions. Among many methods, current annealing appears to be a better way of cleaning the sample due to the possibility of in-situ annealing in the measurement setup. However, long-time current annealing could increase defects in the underlying substrate. Studying the hysteresis with different anneal currents in a graphene device is, therefore, a topic of interest. In this experimental work, we investigate electron/hole transport in a graphene sample in the form of a Hall bar device with a back gate, where the graphene was prepared using chemical vapor deposition on copper foils. We study the hysteresis before and after current annealing the sample by cooling down to a temperature of 35 K from room temperature with a back-gate bias in a closed cycle refrigerator.
INTRODUCTION Graphene is one of the most popular 2D materials [1-7]. It is semimetallic and, has charge carriers that behave like Dirac fermions (zero effective mass) [1]. Graphene also shows high mobilities up to 200,000 cm2V-1s-1 [2], and many other extraordinary effects. Half-integer quantum Hall effect [4] and ballistic transport properties at room temperature [3] are a few examples. Production of high-frequency electronic devices [5] and transparent low resistance conductors [7] will be feasible due to high carrier mobility and lower visible light absorption of graphene. Obtaining disorder free graphene is essential and investigating the obstacles for doing that is crucial for the future of nanotechnology. The highest quality graphene with minimum structural defects is achieved by mechanical exfoliation of pyrolytic graphite [8]. However, the exfoliation method cannot be utilized in creating large-area monolayer graphene. Therefore, a method that can fabricate uniform monolayer graphene in large scale is required. Chemical Vapor Deposition (CVD) of graphene was demonstrated as a
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method of growing single-layer graphene [9]. It has been shown that large area of singlecrystal, monolayer graphene (0.5 mm on a side) can be grown with good control, on copper foils [10-11]. The problem with CVD graphene is the process-induced impurities and defects. Such defects would make our samples inhomogeneous, causing the transport properties to deviate from what we expect theoretically for ideal graphene. Since graphene is zero bandgap s
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