Impact of oxygen adsorption on the electronic properties and contact type of a defective epitaxial graphene-SiC interface

Abstract

Adsorption and dissociation of molecular oxygen on a defective graphene buffer layer (BL) grown on Si-terminated SiC(0001) are herein studied by means of periodic DFT calculations coupled with the nudged elastic band method. We considered a single vacancy (SV) and a divacancy (DV) defective BL on SiC, with or without the uppermost epitaxial monolayer graphene (EG). The adsorption energy of O2 on SV and DV surfaces, producing SV-O and DV-O oxidized systems, is between 2 and 3 times as strong as that on a defect-free BL surface and lacks an energy barrier. In addition, we demonstrate that the n-doping measured in the EG layer of SiC-BL-EG systems, which stems from the charge transfer in the SiC-BL interface, can be fully compensated by oxidizing the DV defective BL. The DV-O-EG interface forms a p-type Schottky contact with a small Schottky barrier height. Instead, a p-type Ohmic contact was measured at the SV-O-EG interface.