Effects of carbon doping on the electronic properties of boron nitride nanotubes: Tight binding calculation

Highlights: • The energy gap is reduced by C-doping due to redistribution of the HOMO and LUMO. • The band gap reduction is sensitive to the number of dopants. • The gap reduction is identical for armchair and zigzag C-doped BNNTs in the electric field. • For C-doped BNNTs, the electronic properties are periodic in the electric field direction. • The band gap decreases linearly for $C_{\mathrm{BN}}^4$ and it is constant at first then decreases for $C_{\mathrm{BN}}^2$. The electronic properties of pure and carbon doped zigzag and armchair Boron Nitride Nanotubes (BNNTs) have been investigated based on tight binding formalism. It was found that the band gap is reduced due to substitution of Boron or Nitrogen atoms by carbon atoms and the doping effects of B- and N-substituted BNNTs are different. The applied electric field converts the carbon doped BNNTs from semiconductor to metal. The gap energy reduction shows an identical dependence to electric field and doping for both armchair and zigzag carbon doped BNNTs. Our results indicate that the band gap of carbon doped BNNTs is a function of the Impurity concentration, electric field strength and the direction between the electric field and dopant location. The band gap for C-doped BNNTs with four carbon atoms decreases linearly but for two carbon atoms, it is constant at first then decreases linearly.