Electric/Magnetic Manipulated Optoelectronic Properties In Silicene And Its Nanoribbons

Silicene is a monolayer silicon film, which owns the graphene-like honeycomb lat-tice. It has been becoming one of the hot topics in condensed matter physics, material science, chemistry and information technologies because of the unique structure and func-tions. Silicene owns the outstanding and special physical and chemical properties than graphene due to its remarkable spin-orbit interaction, other than the significant potential application in optoelectronic and spintronic devices. The quasi-one-dimensional silicene nanoribbon is the unit cell for silicene-based nano-devices and can present the charac-teristic of the quantum confined system, therefore, much attention has been paid to its physical properties. In this thesis, the electronic transport and optoelectronic properties other than its external fields manipulation have been theoretically investigated based on the low-energy effective model under the tight-binding approximation and intersubband transition theorem for semiconductors.The thesis is divided into five chapters. In the first chapter, we give a brief introduc-tion about the discovery, experiment fabrication and electronic structure of silicene, other than the intersubband transition theorem for semiconductors.In chapter two, using the low-energy effective theory and the intersubband transition theorem for semiconductors, we investigate the electronic structure and optical properties of silicene and its external fields manipulation. Based on the low-energy effective Hamilto-nian for silicene, we obtain the system electronic band structure and wave function. Within the framework of intersubband transition theorem for semiconductors, we have obtained the optical transition matrix element, dielectric function, refractive index, extinction co-efficient, absorption coefficient, electron energy loss spectrum and optical conductivity. It has been demonstrated that, the system electronic structure may be modulated to spin degenerate, topological insulated, valley-spin polarized metallic and band insulated states by the electric and/or magnetic field. In the critical electric and/or magnetic field, one observes the quantum phase transition from the topological insulated state to the band insulated one. It has been demonstrated that, the optical response decrease with the increase of the irradiation frequency. Furthermore, the optical transitions from the topo-logical insulated state spin-up and -down subbands are observed to red-/blue-shift with the enhancement of the staggered sublattice potential, respectively, while those from the band insulated state spin-up and -down subbands are proven to be continually blue-shifted with the staggered sublattice potential.In the third chapter, based on the tight-binding approximation and dipole-approximation, using the linear response theory, we study the width-dependent electronic structure, dipole-transition and optical properties for perfect armchair-edge silicene nanoribbons under the irradiation of the electromagnetic filed. It has demonstrated that, the dipole-transition among the smaller indexed valence and conduction subbands for semiconducting 9-/10-and metallic 11-armchair-edge silicene nanoribbons have been demonstrated to be continuously increasing, while those for the larger indexed subbands first increase and then decrease. Furthermore, the optical conductivity and dielectric function for semiconduct-ing 9-/10- and metallic 11-armchair-edge silicene nanoribbons are observed a broad values from infrared to ultraviolet and strongly dependent on the ribbon width and irradiated frequency. The optical response for semiconducting armchair-edge silicene nanoribbons are induced from the transitions between the valence and conduction bands with the same and/or different subband indices, while those for metallic armchair-edge silicene nanorib-bons may only originate from the transitions between the valence and conduction bands with different indices.In chapter four, we investigate the electronic band structure, dipole-transition and optical properties for perfect 8-and 16-zigzag-edge silicene nanoribbons under the irradia-tion of the electromagnetic field. It has been demonstrated that, the optical conductivity, dielectric function and electron energy loss spectrum for 8-and 16-zigzag-edge silicene nanoribbons are observed a broad values from infrared to ultraviolet and sensitively de-pendent on the ribbon width and irradiation frequency. Furthermore, the optical con-ductivity, dielectric function and electron energy loss spectrum for 8- and 16-zigzag-edge silicene nanoribbons originate from the optical transitions between valence and conduction bands with the same subband indices as well as the ones between edge state and bulk state subbands. The obtained results are believed to be useful in exploring the new effects and optoelectronic applications of the silicene-based optoelectronic and spintronic devices.In the fifth chapter, a summary of the work and a outlook of this topic are given.