Electronic structure of two-dimensional germanene crystals

Two-dimensional (2D) germanene crystals, the counterpart of graphene with honeycomb structure, will be an alternative semiconductor material for the next-generation nanoelectronic applications. In this study, we calculated the electronic structure, energy band gap and electron density of germanene using the tight-binding approach and analysed the results of the calculation. First, we developed the model based on the tight-binding theory, and then calculated the electronic structure of germanene. We obtained the 3D energy band structure in the first Brillouin zone for germanene, which has an open energy gap up to 128 meV at the Dirac points K and K′. This open gap shows that germanene is a non-metallic insulator. The first Brillouin zone is almost three times larger than that of graphene because germanene has a larger lattice constant (3·95 Å). The electron density quickly decreases with radial direction, while the density is larger in the center of the Brillouin zone in the angular direction.