Tunable Doping and Optoelectronic Modulation in Graphene-Covered 4H-SiC Surfaces.

Semiconducting graphene is pivotal for the advancement of nanoelectronics due to its unique electronic properties. In this context, silicon carbide (SiC) surfaces have been proposed as ideal supports for inducing semiconducting characteristics in graphene. Here, we employ many-body perturbation theory to investigate the electronic structure and optical properties of graphene-covered 4H-SiC surfaces. Our analysis reveals that pristine 4H-SiC surfaces with dangling bonds exhibit a reduced transport gap and enhanced optically active states within the visible spectrum compared to bulk 4H-SiC. Strong interfacial interactions resulting from the adsorption of a single graphene layer (GL) significantly alter graphene's dispersion, yielding a semiconducting interface with modified optoelectronic properties. While the addition of a second GL restores Dirac dispersion, the two polar faces of the underlying 4H-SiC induce either metallic n-type doping or behavior similar to that of freestanding graphene. Furthermore, we investigate the adsorption of a molecular electron acceptor on SiC covered with one and two GLs. Our findings reveal notable renormalization of the molecular energy levels upon adsorption, resulting in the emergence of distinct new optically excited states. Additionally, a shift in the Fermi level, attributed to partial charge transfer, indicates effective p-type doping. The tunable doping characteristics and optical profiles across various energy ranges highlight the potential of graphene-covered 4H-SiC surfaces as versatile materials for a wide range of technological applications.