Tunable band gap in germanene by surface adsorption

• A band gap is opened at the Dirac point in alkali metal atoms-covered germanene.
• The band gap is induced by the sublattice/bond symmetry breaking of germanene.
• The largest global band gap we obtain is 0.26 eV.
• The effective masses of charge carriers near the Dirac point are very small.
• Germanene can be a candidate of effective transistors channel upon adsorption.

Opening a sizable band gap in the zero-gap germanene without heavy loss of carrier mobility is a key issue for its application in nanoelectronic devices such as high-performance field effect transistors (FETs) operating at room temperature. Using the first-principles calculations, we find a band gap is opened at the Dirac point in germanene by single-side adsorption of alkali metal (AM) atoms. This band gap is tunable by varying the coverage and the species of AM atoms, ranging from 0.02 to 0.31 eV, and the maximum global band gap is 0.26 eV. Since the effective masses of electrons and holes in germanene near the Dirac point after surface adsorption (ranging from 0.005 to 0.106me) are small, the carrier mobility is expected not to degrade much. Therefore germanene is a potential candidate of effective FET channel operating at room temperature upon surface adsorption.