Abstract
The quasiparticle band gaps of semiconducting carbon nanotubes (CNTs) supported on a weakly-interacting hexagonal boron nitride (h-BN) substrate are computed using density functional theory and the GW Approximation. We find that the direct band gaps of the (7,0), (8,0) and (10,0) carbon nanotubes are renormalized to smaller values in the presence of the dielectric h-BN substrate. The decrease in the band gap is the result of a polarization-induced screening effect, which alters the correlation energy of the frontier CNT orbitals and stabilizes valence band maximum and conduction band minimum. The value of the band gap renormalization is on the order of 0.25 to 0.5 eV in each case. Accounting for polarization-induced band gap changes is crucial in comparing computed values with experiment, since nanotubes are almost always grown on substrates.
Highlights
The quasiparticle band gaps of semiconducting carbon nanotubes (CNTs) supported on a weakly-interacting hexagonal boron nitride (h-BN) substrate are computed using density functional theory and the GW Approximation
We have first calculated the electronic band structure according to the local density approximation (LDA) for the isolated (8,0) nanotube, as well as the (8,0) nanotube supported on a monolayer of h-BN
At the density functional theory (DFT) level, the only effect of adding the h-BN substrate in the LDA is the appearance of addition bands well below and above the Fermi level
Summary
The quasiparticle band gaps of semiconducting carbon nanotubes (CNTs) supported on a weakly-interacting hexagonal boron nitride (h-BN) substrate are computed using density functional theory and the GW Approximation. Accounting for polarization-induced band gap changes is crucial in comparing computed values with experiment, since nanotubes are almost always grown on substrates. Since their discovery[1], carbon nanotubes and their unique electronic properties have been an area of great research interest. In the case of semiconducting carbon nanotubes, tight-binding methods[5] and ~k:~p theory[6] predict that the magnitude of the band gap is inversely proportional to the nanotube diameter. This band gap reduction is significant and must be taken into account comparing theoretical values with experimentally measured band gaps of nanotubes grown on substrates
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