Theoretical Studies On The Electron Transport Property Of The Polysilane

Polysilane is composed of lots of Si-Si bonds, theσorbital overlaps one and another between the Si-Si bonds forming a large conjugated system, besides, Silicon atom has the 3d vacant orbital that makes the electron transfer easily, all of which makes the polysilane has the unique photoelectric properties, such as electrical conductivity, thermochromism, UV-absorbing and fluorescence-emission. However, most of the studies on the polysilane still concentrate on the experimental synthesis, and few theoretical studies have been reported. Therefore, it is necessary to study on theσ-conjugated polysilane both theoretically and systematically. In this paper, the electric transport properties of the polysilane are mainly investigated to apply a theoretical basis for the good electric materials.The transport mechanisms of fourσ-conjugated oligosilanes are comparatively studied by combining ATK and Gaussian 03 calculations. It is found that the charge-doped oligosilane Si12+ behaves a remarkable different way in the transmission property from the heteroatom doped Si5BSi6 and Si5PSi6. Charge-doped Si12+ shows nearly no conductivity owing to the damage of the hole transer path by charge-doping. In contrast, Si5BSi6 and Si5PSi6 are demonstrated to be good semiconductors and a NDR behavior is observed for them. This is a reasonable result after the analysis of the transmission spectrums, MPSH states, energy gap, conjugation effect and scattering effect.The electron transport properties of a novel p-n junction nanowire caused by boron-doping and phosphorus-doping are investigated using density functional theory combined with the nonequilibrium Green's functions formalism. A satisfying rectification is observed. This is a reasonable result after the analysis of the MPSH states, transmission spectrum, the frontier orbitals, and the dipole moment. In contrast, the undoped chain has no rectification character. In addition, a NDR behavior is also observed at V=1.8~2.2 V in the doped nanowire and it could be illustrated from the MPSH states and the transmission spectrums.