Tuning the electronic structure of silicene and germanene by biaxial strain and electric field

Abstract

We present a first-principles study of effects of small biaxial strain $(|\ensuremath{\varepsilon}|\ensuremath{\le}5%)$ and perpendicular electric field $(E$-field) on the electronic and phonon properties of low-buckled silicene and germanene. With an increase of the biaxial strain, the conduction bands at the high-symmetric $\mathrm{\ensuremath{\Gamma}}$ and $M$ points of the first Brillouin zone shift significantly towards the Fermi level in both silicene and germanene. In contrast, the $E$-field changes the band dispersions near the $\mathrm{\ensuremath{\Gamma}}$ and open a small band gap at the $K$ point in silicene. We found that the field-induced gap opening in silicene could be enhanced by a compressive strain while mitigated by a tensile strain. This result highlights the tunability of the electronic structure of silicene by combining mechanical strain and electric field.