First principles study of Si-doped BC2N nanotubes

Spin polarized density functional theory is used to investigate the incorporation of substitutional Si atoms in the zigzag (5,0) and in the armchair (3,3) BC2N nanotubes (NTs). Our results show that the Si impurities in BC2N NTs have lower formation energy when compared to Si in carbon and boron nitride NTs. In neutral charge state, Si in the boron site (Si-B) presents a spin split with two electronic levels within the NT band gap and it gives rise to a net spin magnetic moment net of 1 mu(B). Si in the nitrogen site (Si-N) introduces electronic levels near the top of the valence band that lead the system to exhibit acceptor properties, which suggest the formation of defect-induced type-p BC2N NTs. The defective levels for Si in the two nonequivalent carbon atom sites (Si-CI and Si-CII) are resonant with the valence and conduction bands, respectively. The calculations of formation energy in charge state show that for all the available values of the electronic chemical potential, Si-CI and Si-CII have lower formation energy in neutral charge state, while Si-B and Si-N present lower formation energy in neutral or single negative charge state depending on the position of the electronic chemical potential.