Speaker
Description
Working with 2D materials, major limitations are imposed by device reproducibility and yield. The complexity in the fabrication gives rise to an immense number of parameters that have to be controlled. In bilayer graphene devices, the mastery of this parameter space is, to some extent, reflected by the opening of a uniform band-gap under the application of an electric field perpendicular to the bilayer sheet. This gap is theoretically expected and routinely achieved in experiments, but its leanliness as measured by the in-gap resistance is of varying quality and strongly depends on the fabrication details. Clean gaps allow for separating the device from insulating regions by electrostatically gating the Fermi level into the bandgap instead of etching away the material. In the latter approach, the resulting device edges are highly disordered [1], and even though electrostatic device definition has allowed for measurements of clean quantum point contacts [2] and quantum dots [3,4], the device edges themselves have remained less explored. In addition, little attention has been paid to the natural flake edges, which may still provide some conducting paths in typical gate-defined geometries.
In our attempt to increase device yield and reproducibility, we have conceived a new design of dual-gated bilayer graphene devices. Taking into consideration concerns about Cr and Ti sticking layers [5] and following recent trends in the field [6,7], we move away from metal as top-gate electrode, but instead rely on graphite layers. Our devices are designed in a way that keeps the active area unaffected from exposure to polymers or high-voltage electron beams used in typical lithography processes. Importantly, the active area is fully isolated from the natural flake edges. We characterize our device architecture by performing magnetotransport measurements on different device geometries, including field-effect transistors, a Hall bar, and an Aharonov-Bohm ring. We assess the general device quality by extracting band-gap resistance and uniformity, mobility, and coherence length. In addition, we perform detailed analyses on the scattering effects at the device boundaries and discuss the parameter regimes in which nano-scale devices like quantum dots are preferably operated.
References
[1] D. Bischoff, P. Simonet, A. Varlet, H. C. Overweg, M. Eich, T. Ihn, and K. Ensslin, Phys. Status Solidi RRL 10, 68 (2016).
[2] H. Overweg, H. Eggimann, X. Chen, S. Slizovskiy, M. Eich, R. Pisoni, Y. Lee, P. Rickhaus, K. Watanabe, T. Taniguchi, V. Fal’ko, T. Ihn, and K. Ensslin, Nano Lett. 18, 553 (2018).
[3] M. Eich, R. Pisoni, A. Pally, H. Overweg, A. Kurzmann, Y. Lee, P. Rickhaus, K. Watanabe, T. Taniguchi, K. Ensslin, and T. Ihn, Nano Lett. 18, 5042 (2018).
[4] L. Banszerus, B. Frohn, A. Epping, D. Neumaier, K. Watanabe, T. Taniguchi, and C. Stampfer, Nano Lett. 18, 4785 (2018).
[5] W. Zheng, K. Zhu, S. Pazos, Y. Shen, Y. Yuan, O. Alharbi, Y. Ping, and M. Lanza, Appl. Surf. Sci. Adv. 29, 100820 (2025)
[6] A. A. Zibrov, C. Kometter, H. Zhou, E. M. Spanton, T. Taniguchi, K. Watanabe, M. P. Zaletel, and A. F. Young, Nature 549, 360 (2017).
[7] E. Icking, D. Emmerich, K. Watanabe, T. Taniguchi, B. Beschoten, M. C. Lemme, J. Knoch, and C. Stampfer, Nano Lett. 24, 11454 (2024).