A novel phase of germagraphene — Quasi-direct bandgap and anisotropic carrier mobility with potential optoelectronic response

Abstract

The experimental feasibility of implanting germanium into single-layer graphene (ACS Nano 12 2018 4641) motivates us to propose a new phase of monolayer rectangular germa-graphene (R-GeC${}_3$) using first-principles calculations. In this article, we predict and critically explore a novel formation of germa-graphene monolayer with all its structural intricacies, underlying electronic nature, carrier mobility and relaxation time scales added with the subsequent optical response. This novel monolayer exhibits a semiconducting electronic nature with a quasi-direct bandgap of 0.40 eV at a non-high-symmetry location in the Brillouin zone. Lower deformation potential values indicate relatively weaker electron–phonon scattering, facilitating ultrahigh carrier mobility and picosecond order relaxation times. Tiny and anisotropic carrier effective masses suggest rapid carrier transport properties and increase the efficiency of photogenerated electron–hole separation. The optical signatures of this proposed rectangular germa-graphene have been compared with the well-established form of rhombohedral GeC${}_3$. The real part of the dielectric function indicates the presence of plasma frequency in the parallel polarization direction, signifying a transition from metallic to dielectric behavior. Both the proposed R-GeC${}_3$ and its rhombohedral variants are observed to absorb excitations all over the visible, infrared and near-infrared regimes with detectable birefringence. Such exotic features are key indicative of this R-GeC${}_3$ being one of the better choices for transport and optoelectronic sectors.