A comparative computational study of the electronic properties of planar and buckled silicene

TL;DR

This study compares the electronic properties of planar and buckled silicene using density functional calculations, revealing a direct band gap in buckled silicene and its potential for silicon-based nano-electronics.

Contribution

It is the first to report a direct band gap in silicene, highlighting its compatibility with existing silicon technology and potential applications.

Findings

Planar silicene is gapless with mass-less Dirac fermions.

Buckled silicene has a small direct band gap of about 25 meV.

Dirac fermions in silicene have about half the Fermi velocity of graphene.

Abstract

Using full potential density functional calculations within local density approximation (LDA), we report our investigation of the structural electronic properties of silicene (the graphene analogue of silicon), the strips of which has been synthesized recently on Ag(110) and Ag(100) surfaces. An assumed planar and an optimized buckled two dimensional (2D) hexagonal structures have been considered for comparisons of their electronic properties. Planar silicene shows a gapless band structure analogous to the band structure of graphene with charge carriers behaving like mass-less Dirac fermions, while the structurally optimized buckled silicene shows a small direct energy band gap of about 25 meV (at the K point of the hexagonal Brillouin zone) in its electronic structure and the charge carriers in this case behave like massive Dirac fermions. The actual band gap would be larger than this as LDA is known to underestimate the gap. The average Fermi velocity of the Dirac fermions in silicene was estimated at about half the value experimentally measured in graphene. These properties of silicene are attractive for some of the applications one envisages for graphene. Our finding of a direct band gap in silicene is something new. The results, if verified by experiments, are expected to have huge industrial impact in the silicon-based nano-electronics and nano-optics because of the possible compatibility silicene with current silicon-based micro-/nano technology.