Band structure of the carbon doped zigzag boron nitride nanotubes (BNNTs) is calculated by a simple tight-binding model. It was found that the doping effect of B-substituted and N-substituted BNNT is different and carbon substitution for either boron or nitrogen in BNNTs reduces the band gap. Investigations show the dependence of band gap to the axial magnetic and transverse electric fields for C-doped BNNTs. The applied high electric field causes transition from semiconductor to conductor in C-doped BNNTs. The band gap of C-doped BNNTs oscillates as a function of magnetic flux with period |1 in the magnetic fields. Influence of C-doping on the absorption spectrum is also discussed in this paper.

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