Doping effects on metallic and semiconductor single wall carbon nanotubes

Francesco Buonocore (1)

1 STMicroelectronics

In this paper we investigate nitrogen and boron doped zig-zag and armchair single wall carbon nanotubes (SWNTs) with theoretical models based on the density functional theory. We take into account nitrogen and boron doping for two isomers in which substitutive atoms are on opposite sides of the tube, but only in one isomer the impurity sites are symmetrical with respect to the diameter. The band structures show a strong hybridization with impurity orbitals that change the original band structure. Although the two isomers of armchair SWNT exhibit the same formation energy, their band structures are different. Indeed asymmetrical isomers are gapless and exhibit a crossing of valence and conduction bands at k=π/a, leading to metallic SWNTs. Band structures of symmetrical isomers, on the other hand, exhibit an energy gap of 0.4 eV between completely filled valence band and empty conduction band. We use density of charge in order to understand this difference. In zig-zag SWNT an impurity band is introduced in the energy gap and for N doping this band is just partially occupied in such a way that the electronic behaviour is reversed from semiconductor to metallic. While for a given isomer armchair SWNT shows similar behaviours of N and B doped structures, B doped zig-zag SWNTs present different band structure and occupation compared to the N doped case.

Mots clés: Physical Sciences

Francesco Buonocore. Doping effects on metallic and semiconductor single wall carbon nanotubes. Philosophical Magazine, 2007, 87 (07), pp.1097-1105. ⟨10.1080/14786430601032352⟩. ⟨hal-00513792⟩