First-principles Investigation Of Structure And Application Of Bi-series Materials

Bi2X3(X=Se,Te,S) are three important semi-conductors among VB-VIB group, and have attached much attention due to their unique properties. All the electronic structures of bulk, film, surface and that doped with atoms were investigated systematically by first-principles and the changes of electronic structures from the original structure to doped structure were also investigated. The main contents in this paper are as follows:Firstly, the electronic structures of Bi2Se3 were investigated. The results show that the original bulk is a direct band gap semi-conductor with a 0.32 e V gap which agree well with the experimental value. The valence and conduction band are composed of p states of Se and Bi; The arrangement of Se(1) layer will changes while the single-QL(quintuple layer, QL) film is doped with Pb and the influence is mainly caused by the changed Se(1/) layer. The Bi 6s state has a modulation role on the top of the valence band and this will keep the bulk to be a direct band gap semiconductor. For film, the influence of Bi 6s state at the top of valence band decreases significantly and this weak modulation causes the top of valence band deviate from the bottom of conduction band, the band gap also changes from direct band gap to indirect band gap. The band gap decreases about 11.5% while single-QL film doped with Al, and decreases further while double-QL doped with Al. The band structure of film under the plane strain mainly reflects in the band gap values linear with the strain rate.Secondly, the electronic structures of Bi2Te3 was also calculated. The results show that the bulk of Bi2Te3 is a direct band gap with the value of 0.177 e V. And the results indicate that the spin orbit coupling has no significant effect on the electronic structures. The single-QL film shows an obvious indirect band gap and the value is about 1.031 e V. The indirect band gap of double-QL film is about 3.122 e V. The film under the plane strain mainly reflects in the band gap values linear with the strain rate. In addition, the slops are different according to the thickness.Finally, the electronic structures of Bi2S3 was also calculated. The results show that the pnma Bi2S3 is indirect band gap semiconductor, but the position of the top of valence band is not obvious and the band gap is about 1.198 e V. The Bi2S3 bulk does not show obvious changes when doped with Se and Te atom and this is mainly because of the approximation of Se/Te with S. The band gap are 1.186 e V and 1.001 e V respectively, and the difference mainly comes from the adjustment of the periodic potential field. Bi2S3(R-3m structure) is a direct band gap semiconductor with the band gap about 1.046 e V,which provides reference for the experimental exploration.