Quality assessment of graphene: Continuity, uniformity, and accuracy of mobility measurements
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With the increasing availability of large-area graphene, the ability to rapidly and accurately assess the quality of the electrical properties has become critically important. For practical applications, spatial variability in carrier density and carrier mobility must be controlled and minimized. We present a simple framework for assessing the quality and homogeneity of large-area graphene devices. The field effect in both exfoliated graphene devices encapsulated in hexagonal boron nitride and chemical vapor-deposited (CVD) devices was measured in dual current–voltage configurations and used to derive a single, gate-dependent effective shape factor, β, for each device. β is a sensitive indicator of spatial homogeneity that can be obtained from samples of arbitrary shape. All 50 devices investigated in this study show a variation (up to tenfold) in β as a function of the gate bias. Finite element simulations suggest that spatial doping inhomogeneity, rather than mobility inhomogeneity, is the primary cause of the gate dependence of β, and that measurable variations of β can be caused by doping variations as small as 1010 cm−2. Our results suggest that local variations in the position of the Dirac point alter the current flow and thus the effective sample shape as a function of the gate bias. We also found that such variations lead to systematic errors in carrier mobility calculations, which can be revealed by inspecting the corresponding β factor.
KeywordsCVD graphene doping inhomogeneity electrical measurements van der Pauw hBN-encapsulated graphene finite element simulations Raman mapping
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We would like to thank the Nanocarbon group at DTU Nanotech for valuable discussions as well as the staff at DTU Danchip for technical and fabrication advice. For funding we would like to acknowledge DNRF103 CNG, HC Ørsteds foundation, Villum Fonden project (No.VKR023117), the DA-GATE project (No. 12-131827), and EC Graphene FET Flagship contract number 604391 as well as H2020 European projects (Nos. 692527 and 688225).
- Wang, R. Z.; Whelan, P. R.; Braeuninger-Weimer, P.; Tappertzhofen, S.; Alexander-Webber, J. A.; Van Veldhoven, Z. A.; Kidambi, P. R.; Jessen, B. S.; Booth, T.; Bøggild, P. et al. Catalyst interface engineering for improved 2D film lift-off and transfer. ACS Appl. Mater. Interfaces 2016, 8, 33072–33082.CrossRefGoogle Scholar
- van der Pauw, L. J. A method of measuring the resistivity and Hall coefficient on lamellae of arbitrary shape. Philips Tech. Rev. 1958, 20, 220–224.Google Scholar
- Lotz, M. R.; Boll, M.; Østerberg, F. W.; Hansen, O.; Petersen, D. H. Mesoscopic current transport in two-dimensional materials with grain boundaries: Four-point probe resistance and Hall effect. Appl. Phys. Lett. 2016, 120, 134303.Google Scholar