  The electronic properties of aluminum-doped graphenes enriched by
multi-orbital hybridizations are investigated using first-principles
calculations. The feature-rich electronic structures exhibit the quasi-rigid
red shifts of the carbon-created energy bands, the Al-dominated valence and
conduction bands, and many free electrons in the conduction Dirac cone. These
are directly reflected in the special structures of density of states (DOS).
The Al- and alkali-induced high free carrier densities are almost the same.
There exist certain important differences among the Al-, alkali- and
halogen-doped grapehenes, such as, the buckled or planar graphene, the
preserved or seriously distorted Dirac cone, the existence of the
adatom-dominated valence bands, the free electrons or holes, the degenerate or
splitting spin-related states, and the simple or complicated peaks in DOS. The
similarities and differences mainly come from the diverse orbital
hybridizations in adatom-C bonds, as indicated from the atom-dominated bands,
the spatial charge distributions and the orbital-projected DOS.
