Crystal Structures and Electronic Properties of Single-Layer, Few-Layer, and Multilayer GeH

Abstract

Single-layer germanane (GeH) structures have been explored using evolutionary algorithms combined with first-principles methods. The chair GeH is the most stable structure among all uncovered single-layer GeH structures, which is similar to what is found in graphane. Multilayer and few-layer GeH structures with 2–6 layers in their unit cells are constructed from the chair GeH in various possible stacking sequences. Many isoenergetic multilayer GeH structures are found using the semiempirical dispersion correction of DFT-D3. It is shown that the experimentally synthesized bulk GeH [Bianco ACS Nano 2013, 7, 4414] assumes the tr6 structure, not the previously claimed 2H structure. Band structure calculations reveal that the location of the direct band gap of multilayer GeH structures oscillates between the Γ and A point in their first Brillouin zone depending on whether the unit cell contains an odd or even number of layers. The band gaps of multilayer and few-layer chair GeH structures are calculated to lie between 1.47 and 1.66 eV using the hybrid HSE06 functional, and they are dependent on the stacking sequences and interlayer distances.