Polysilane-Wrapped Carbon and Boron-Nitride Nanotubes: Effects of B or P Doping on Electron Transport

We perform a comprehensive study of effects of wrapping either undoped or doped polysilane (PSi) around the outer surface of a carbon nanotube (CNT) or a boron-nitride nanotube (BNNT) using density functional theory and nonequilibrium Green's function calculations. For CNT, because the wrapping of either undoped PSi or B-doped PSi has little effect on the electronic band structure near the Fermi surface E_f, the conductivity of the wrapped CNT is still dominated by the CNT π state. This behavior is also confirmed by using the two-probe device model system with a unit cell of undoped or B-doped PSi-wrapped CNT sandwiched between two Au electrodes. For P-doped PSi/CNT, the P dopant can introduce electron donor state in the valence band. However, such a P-dopant effect is still suppressed and the conductivity is still controlled by the CNT π state based on the two-probe device computation. Contrary to CNT, the PSi-wrapped BNNT can markedly influence the band structure of the BNNT. The wrapping of either undoped or doped PSi can significantly increase the conductivity. For undoped PSi/BNNT, the valence band stems from the BNNT π state while the conduction band stems from the PSi σ state. For B-doped PSi/BNNT, B atoms introduce an electron-acceptor band just above the E_f, whereas in the P-doped PSi/BNNT, P atoms introduce an electron-donor band just below the E_f. For the B-doped PSi/BNNT two-probe system, the B-dopant state can participate in electron transport and exhibit a notable negative differential resistance (NDR) feature. However, for the P-doped PSi/BNNT two-probe system, the P-dopant contribution is suppressed, akin to the P-doped PSi/CNT system.