Atypical quantized resistances in millimeter-scale epitaxial graphene p-n junctions

Dinesh Patel^1,2*, Martina Marzano^1,3,4, Mattias Kruskopf^1,5,6, Hanbyul Jin^1,5, David B. Newell¹, Chi-Te Liang², Randolph E. Elmquist¹, Albert F. Rigosi¹

¹Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland, USA
²Department of Physics, National Taiwan University, Taipei, Taiwan
³Department of Electronics and Telecommunications, Politecnico di Torino, Torino, Italy
⁴Istituto Nazionale di Ricerca Metrologica, Torino, Italy
⁵Joint Quantum Institute, University of Maryland, College Park, Maryland, USA
⁶Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany

* Presenter:Dinesh Patel, email:dkpjnp@gmail.com

Graphene has been extensively studied because of its unique electrical and optical properties. Epitaxial graphene (EG) on silicon carbide (SiC), which grows on hexagonal SiC at high temperatures, can be nearly defect-free on the centimeter scale and exhibits properties that make it suitable for large-scale and high-current applications (1). We have demonstrated the millimeter-scale fabrication of monolayer epitaxial graphene p-n junction devices using simple ultraviolet photolithography, thereby significantly reducing device processing time compared with electron beam lithography typically used for obtaining sharp junctions. This work presents the resulting variety of experimental data obtained from these devices, introducing multiple current inputs with several different configurations. Furthermore, we use the LTspice circuit simulator (2) to examine the various rearrangements of the electric potential in the device when injecting current at up to three independent sites. These measurements yield nonconventional, fractional multiples of the typical quantized Hall resistance at the ν=2 plateau (R_H=h ⁄ (2e²)), where R_H is the Hall resistance, h is the Planck constant and e is the electron charge) that take the form: (a/b) R_H. Here, a and b have been observed to take on values such as 1, 2, 3, and 5 to form various coefficients of R_H. These results support the potential for drastically simplifying p-n junction device processing time and it is useful in resistance metrology for the scaling to different decade values of the electrical resistance measured in ohm.

References:
[1] Kruskopf, M., et al., 2D Mater. 3, 041002 (2016).
[2] Ortolano, M., et al., Meas. Sci. Technol. 26, 085018 (2015).

Keywords: Graphene, Quantum Hall Effect, Ultraviolet Photo-Lithography, p-n junction, LTspice circuit simulator