Strain-induced Energy Band-gap Opening of Silicene.

Inspired by the success of graphene, various two dimensional (2D) structures on different substrates have been proposed. Among others, an allotropic form of silicon, coined "silicene" was shown to exhibit similar properties with graphene of a zero band gap and a Dirac cone shape at the K point in the Brillouin zone. Similar to its counterpart graphene, one of the main obstacles to applying silicene in modern electronics is the lack of an energy band gap. In this work, a systematic study was presented on the structural and electronic properties of single and bi-layered silicon films under various in-plane biaxial strains. The modeling was performed using density functional theory. The atomic structure of the 2D silicon films was optimized and verified by using both the local-density approximations and generalized gradient approximations. Energy band diagram, electron transmission efficiency, and the charge transport property were calculated. It turns out that single free-standing 2D silicon film, i.e. silicene, does not present any energy band gap opening under biaxial tensile/compressive in-plane strain/stress, while bi-layered silicon film exhibits an energy band gap as the applied in-plane tensile strain reaches above 10.7%. In addition, the energy band gap of the bi-layered silicon film shows a linear dependency on the applied in-plane strain and reaches a maximum of about 168.0 meV as the in-plane tensile strain reaches ~ 14.3%. Single and bi-layered silicon films grown on various common semiconductor substrates have been modeled. By choosing the proper substrate, an energy band gap can be opened for the bi-layered silicon film. This will provide an opportunity for applying 2D silicon structure in the mainstream IC industry.