  We investigate a disordered single-walled carbon nanotube (SWCNT) in an
effective medium super cell approximation (EMSCA).
  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.Second type of disorder considered is a
substitutional $B_{cb}N_{cn}C_{1-cb-cn}$ alloy due to it's 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 at a critical concentration it disappears. A consequence
of our results for nano electronic devices is that by changing the
boron(nitrogen) concentration, one can make a semiconductor SWCNT with a
pre-determined energy gap.
