Band gap unification of partially Si-substituted single wall carbon nanotubes

TL;DR

This study investigates how silicon substitution in single wall carbon nanotubes affects their electronic properties, revealing band gap unification and enhanced optical transitions, with potential implications for nanoelectronic applications.

Contribution

It provides a detailed analysis of the electronic structure changes due to Si substitution in various SWCNTs using band structure calculations, highlighting the unification of band gap characteristics.

Findings

Si substitution opens and unifies band gaps across different SWCNT types.

Silicon substitution significantly increases optical transition probabilities in the near infrared.

Regular Si atom distribution is energetically more favorable than random distribution.

Abstract

The atomic and electronic structure of a set of pristine single wall SiC nanotubes as well as Si-substituted carbon nanotubes and a SiC sheet was studied by the LDA plane wave band structure calculations. Consecutive substitution of carbon atoms by Si leads to a gap opening in the energetic spectrum of the metallic (8,8) SWCNT with approximately quadratic dependence of the band gap upon the Si concentration. The same substitution for the semiconductor (10,0) SWCNT results in a band gap minimum (0.27 eV) at ~25% of Si concentration. In the Si concentration region of 12-18%, both types of nanotubes have less than 0.5 eV direct band gaps at the Gamma-Gamma point. The calculation of the chiral (8,2) SWSi_0.15C_0.85NT system gives a similar (0.6 eV) direct band gap. The regular distribution of Si atoms in the atomic lattice is by ~0.1 eV/atom energetically preferable in comparison with a random distribution. Time dependent DFT calculations showed that the silicon substitution sufficiently increases (roughly by one order of magnitude) the total probability of optical transitions in the near infrared region, which is caused by the opening of the direct band gap in metallic SWCNTs, the unification of the nature and energy of band gaps of all SWCNT species, the large values of <Si3p|r|Si3s> radial integrals and participation of Si3d states in chemical bonding in both valence and conductance bands.