Effect of stacking mode on electronic structure and optical properties of bilayer germanene

The electronic structure and optical properties of germanene and three type of bilayer germanene have been studied by first-principles calculation method. The results show that the stable germanene exhibits warped structure. Monolayer germanene exhibits massless Dirac Fermion near K-point, while bilayer germanene exhibits anisotropy Dirac bands. Meanwhile, in order to control the energy band structure, the band gap of bilayer germanene is adjusted by changing the interlayer distance and stacking mode. At the optimal layer spacing, the band gap of bilayer germanene appears at the K-point with 0.417eV, and the phase transition from semiconductor to metal can be realized by further changing the stacking mode. In terms of optical properties, bilayer germanene has better optical response. The results show that the band gap of bilayer germanene can be modulated successfully using stacking mode. These findings are of great significance to the modulation of electronic structure of germanene and the application of germanene in the field of Dirac band materials.