Charge transfers and charged defects in WSe₂/graphene-SiC interfaces

Area of Science:

• Materials Science
• Condensed Matter Physics
• Surface Science

Background:

• Vertical heterojunctions are crucial for advanced electronic devices.
• Understanding charge transfer at interfaces is key to optimizing device performance.
• Tungsten diselenide (WSe2) and graphene are promising 2D materials for such applications.

Purpose of the Study:

• To investigate charge transfer mechanisms in WSe2/graphene vertical heterojunctions.
• To determine the origin of interface dipoles.
• To validate the applicability of the Schottky-Mott model.

Main Methods:

• Kelvin probe force microscopy (KPFM) for experimental surface potential measurements.
• Density functional theory (DFT) for atomic-level simulations of electronic structure and charge distribution.
• Fabrication of WSe2/graphene heterojunctions on silicon carbide substrates.

Main Results:

• Experimental evidence of an interface dipole was observed.
• DFT confirmed electron transfer from n-doped graphene to the WSe2 layer, neutralizing the doping.
• KPFM showed a constant vacuum level shift with varying graphene layers, supporting the Schottky-Mott model.
• DFT indicated that the first WSe2 layer captures most excess charge, with minimal influence from subsequent layers.
• Charged defects at WSe2 edges impact the electrostatic landscape.

Conclusions:

• Charge transfer is the dominant mechanism governing the electronic properties of WSe2/graphene heterojunctions.
• The Schottky-Mott model accurately describes these interfaces when considering charge transfer.
• Interface dipole formation is primarily driven by the initial WSe2 layer and graphene doping levels.