Disordered carbon nanotube alloys in the effective-medium supercell approximation

We investigate a disordered single-walled carbon nanotube (SWCNT) in an effective-medium supercell approximation (EMSCA). The first type of disorder that we consider is the presence of vacancies. Our results show that the vacancies induce some bound states on their neighbor host sites, leading to the creation of a band around the Fermi energy in the SWCNT average density of states. The second type of disorder considered is a substitutional BcbNcnC1-cb-cn alloy due to its applications in hetrojunctions. We found that for a fixed boron (nitrogen) concentration, by increasing the nitrogen (boron) concentration the averaged semiconducting gap E-g decreases and disappears at a critical concentration. A consequence of our results for nanoelectronic devices is that by changing the boron (nitrogen) concentration, one can make a semiconductor SWCNT with a predetermined energy gap.