Isoelectronically substituted group-III based monolayers: An ab initio study

Abstract

Using density functional theory based electronic structure calculations, we carry out detailed investigation on geometric and electronic properties of group-III atom (B, Al, and Ga) based monolayers, namely borophene, aluminene, and gallinene, in ${\ensuremath{\beta}}_{12}$ configuration which is one of the stable structures for borophene. The results of our calculations indicate that all these monolayers form energetically stable systems and these are all metallic in nature since they possess finite density of states at the Fermi level. Analysis of optimized geometric structures reveals that while borophene in ${\ensuremath{\beta}}_{12}$ structure stabilizes in planar structure, the geometries of the remaining monolayers are nonplanar. In the case of borophene, there is a signature of crossing of two linear bands (which form Dirac cones) at about 2 eV and 0.5 eV above the Fermi level. Similar features have also been observed in electronic band structures of both aluminene and gallinene. Interestingly, one of the Dirac cones in these monolayers lies much closer to the Fermi level compared to the borophene case. The Fermi velocities around these Dirac cones are also higher and comparable to that in graphene. We further study the effect of isoelectronic substitution at one of the inequivalent sites (C site) of the ${\ensuremath{\beta}}_{12}$ configuration for these three monolayers. Our results show that borophene still retains its planar geometry following the substitution. Interestingly, in all these cases, crossing of linearly dispersing bands (Dirac cones) is observed nearer to the Fermi level compared to the pristine systems. Our study suggests that isoelectronic substitutions may be useful in tuning the electronic properties, in particular linear dispersion, of monolayer systems.