Atomic-Scale Characterization of Graphene p-n Junctions for Electron-Optical Applications

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Graphene p-n junctions are explored for ballistic solid-state devices, enabling electron trajectory control via collimation and focusing.
• The performance of these junctions critically depends on their doping profile and interface roughness.

Purpose of the Study:

• To atomically characterize graphene p-n junction geometries and doping profiles.
• To evaluate the impact of junction quality on electron focusing and collimation.
• To provide guidance for optimizing graphene p-n junction fabrication.

Main Methods:

• Utilized four-probe scanning tunneling microscopy and spectroscopy (STM/S) to analyze two graphene p-n junction types.
• Performed spectroscopic imaging to map local doping profiles.
• Employed non-equilibrium Green's function (NEGF) simulations incorporating experimental data.

Main Results:

• Identified non-idealities in both geometry and doping profiles of realistic graphene p-n junctions.
• Demonstrated that natural graphite gates improve junction geometry compared to CMOS polySi gates.
• Quantified roughness and doping profiles, finding that minimizing lateral interface roughness and junction width is crucial for Veselago focusing.

Conclusions:

• Natural graphite gates offer superior geometry for graphene p-n junctions.
• Achieving efficient electron focusing and collimation requires minimizing interface roughness and junction width.
• Non-linearity in doping profiles currently limits carrier collimation performance.