We find that for realizing Veselago focusing, it is crucial to minimize lateral interface roughness which only natural graphite gates achieve and to reduce junction width, in which both devices under investigation underperform. We quantify the geometric roughness and doping profiles of junctions experimentally and use these parameters in non-equilibrium Green's function-based simulations of focusing and collimation in these realistic junctions. We show that the geometry of the junction can be improved by using the cleaved edge of van der Waals metals such as graphite to define the junction. We find that realistic junctions exhibit non-ideality both in their geometry as well as in the doping profile across the junction. Using spectroscopic imaging, we characterize the local doping profile across and along the p-n junctions.
Here, we use four-probe scanning tunneling microscopy and spectroscopy (STM/STS) to characterize two state-of-the-art graphene p-n junction geometries at the atomic scale, one with CMOS polySi gates and another with naturally cleaved graphite gates. The ability of p-n junctions to control electron trajectories depends crucially on the doping profile and roughness of the junction. Graphene p-n junctions offer a potentially powerful approach toward controlling electron trajectories via collimation and focusing in ballistic solid-state devices. 9 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.8 Department of Physics, University of Virginia, Charlottesville, Virginia 22904, United States.7 College of Nanoscale Science and Engineering, The State University of New York at Albany, Albany, New York 12203, United States.6 Microsystems Technology Laboratories, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.5 Intel Corporation, Santa Clara, California 95054, United States.4 Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, Virginia 22904, United States.3 Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai 200438, P.R.Watson Research Center, Yorktown Heights, New York 10598, United States. 1 Department of Physics, Columbia University, New York, New York 10027, United States.
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