Theoretical Study On The Electronic Structures And Charge Transport Properties Of Some Semiconductors

The electronic structures and transport properties of semiconductors are the key criteria for designing and searching novel semiconductors with excellent property.After decades of rapid development,the electronic structures and transport properties of semiconductors has become one of the most popular research topics in the world.In this dissertation,theoretical studies on the electronic structures and transport properties of some different kinds of semiconductors are performed,including one-dimensional DNA/RNA,two-dimensional layerd semiconductors and three-dimensional solid(bulk)materials.In chapter ?,the development of semiconductor materials and their further applications are briefly summarized.After that,some novel semiconductors with rapidly development in recent years such as molecular wire,two-dimensional layerd semiconductor as well as organic-inorganic hybrid perovskite materials,are introduced as representatives due to their potentially applications in many fields.In chapter ?,the basis of the quantum chemistry and the mechanisms of charge transport in semiconductors are discussed in detail.Two charge transport models,the hopping model and the band-like model,are introduced.The hopping model is mainly used to describe the charge behavior in organic semiconductors whose charge transport is determined by both electronic and electroacoustic coupling.The electroacoustic coupling in organic semiconductors is close to or even larger than the electronic coupling.On the other hand,the band-like model is usually used to describe the charge behavior in inorgainic semiconductors and some organic semiconductors with strong electronic coupling,in which the charge scatted by phonon transfers along the band.In chapter ?,the transfer rates and carrier mobilities of twelve different kinds of DNA/RNA are simulated,using hopping model based on Marcus theory.Our results are consistent well with the experimental ones,indicating that the hopping model can well describe the charge transport in DNA/RNA.Additionally,we find that DNA/RNA with proper?-? stack can significantly improve the carrier mobility.Among all the simulated DNA/RNA,the carrier mobility of 2L8I even reaches 1.09×10-1 cm2V-1s-1,at the same order of discotic liquid crystal.Therefore,2L8I can be further used as the potential material in molecular wire.In chapter IV,transport properties of the two-dimensional semiconductors BNC,are systematically calculated on the basis of deformation potential approximation and Boltzmann transport theory.Our results show that all structures have non-zero band gaps,and while the gap is affected by the ratio of C as well as the atomic arrangement of C.Furthermore,the carrier mobilitity of BNC2-1 reaches 105 cm2 V-1s-1,higher than graphene in specific directions.BNC and BNC4 monolayers have obvious anisotropic hole and electron mobilities,especially for BNC4,of which the hole mobility along y direction and the electron mobility along x direction almost reach 106 cm2V-1s-1,even higher than those of graphene.In chapter V,the perovskites MABI3 with three different phases and 27 kinds of different divalent metals are screened by GLLB-SC functional.The calculated results are in accordance well with experimental results.Among studied perovskites,five of them(MABI3:B=Pb,Sn,Ge,Cd,Be)have proper gaps for solar cell,and three of those have already been confirmed by experiments.Additionally,the electronic structure of double perovskite MA2AgSbI6 is calculated.The band gap of MA2AgSbI6 is 2.0 eV and the electron effective mass of MA2AgSbI6is close to that of MAPbI3,indicating its good electron transport property.The partial charge density shows that the electron and hole in the lattice can be effectively separated.Finally,the band gap of MA2AgSbI6 is comfirmed by our experimental result,which means MA2AgSbI6is one of the potential perovskite structures for solar cell.In chapter VI,based on the experimental fact that the hydrogen evolution reaction(HER)performace is associated with the facet of the CoPS,we calculate the electronic structure of CoPS,and later on,construct different facets to study the H adsorption/desorption process.The calculations show explicit modeling of both H adsorption and H-H recombination steps allows for a comprehensive description of the overpotential dependence of the HER activity.The combined experimental and theoretical study thus provides a unique mechanistic insights into the facet dependence of HER processes on new non-noble metal electrocatalysts,and thus crucial insights into the design of advanced nanostructured HER catalysts.