# Edge states and ballistic transport in zig-zag graphene ribbons: the role of SiC polytypes

## TL;DR

This study reveals that the ballistic transport in zig-zag graphene ribbons grown on SiC substrates depends critically on the SiC polytype, with only 6H-SiC supporting ballistic edge states, unlike 4H-SiC.

## Contribution

It demonstrates that SiC polytype influences the electronic properties and ballistic nature of graphene ribbons, highlighting the importance of substrate choice in graphene device fabrication.

## Key findings

- Ballistic graphene ribbons only grow on 6H-SiC.
- 4H-SiC ribbons are diffusive and lack edge states.
- H2 passivation restores metallicity but not edge states.

## Abstract

Zig-zag edge graphene ribbons grown on 6H-SiC facets are ballistic conductors. It has been assumed that zig-zag graphene ribbons grown on 4H-SiC would also be ballistic. However, in this work we show that SiC polytype matters; ballistic graphene ribbons only grow on 6H SiC. 4H and 4H-passivated ribbons are diffusive conductors. Detailed photoemmision and microscopy studies show that 6H-SiC sidewalls zig-zag ribbons are metallic with a pair of n-doped edge states associated with asymmetric edge terminations, In contrast, 4H-SiC zig-zag ribbons are strongly bonded to the SiC; severely distorting the ribbon's $\pi$-bands. $\text{H}_2$-passivation of the 4H ribbons returns them to a metallic state but show no evidence of edge states.