Highly effective gating of graphene on GaN

By using four-layered graphene/gallium nitride (GaN) Schottky diodes with an undoped GaN spacer, we demonstrate highly effective gating of graphene at low bias rendering this type of structure very promising for potential applications. An observed Raman G band position shift larger than 8.5 cm-1 corresponds to an increase in carrier concentration of about 1.2.1013 cm-2. The presence of a distinct G band splitting together with a narrow symmetric 2D band indicates turbostratic layer stacking and suggests the presence of a high potential gradient near the Schottky junction even at zero bias. An analysis based on electroreflectance measurements and a modified Richardson equation confirmed that graphene on n-GaN separated by an undoped GaN spacer behaves like a capacitor at reverse bias. At least 60% of G subband position shifts occur at forward bias, which is related to a rapid reduction of electric field near the Schottky junction. Our studies demonstrate the usefulness of few layer turbostratic graphene deposited on GaN for tracing electron-phonon coupling in graphene. Multilayer graphene also provides uniform and stable electric contacts. Moreover, the observed bias sensitive G band splitting can be used as an indicator of charge transfer in sensor applications in the low bias regime.

Automated summary

The study demonstrates effective gating of graphene at low bias using four-layered graphene/gallium nitride (GaN) Schottky diodes and undoped GaN spacer, suggesting their potential for applications. The observed Raman G band position shift and splitting indicate turbostratic layer stacking and high potential gradient near the Schottky junction. Analysis based on electroreflectance measurements and a modified Richardson equation confirms graphene behavior as a capacitor at reverse bias on n-GaN separated by an undoped GaN spacer.