Study On Structures And Electronic Properties Of Si Nanowires Based On Density Functional Tight Binding

With the rapid development of modern microelectronics industry,the energy supply and refrigeration demand of device put forward higher requirements.Therefore,We need develop thermoelectric materials of high Seebeck coefficient,high conductivity and low thermal conductivity,which can realize high-efficiency two-way conversion between electricity and heat.The value ZT of silicon nanowires is high at room temperature,and with the decrease of the diameter of nanowires,at low temperatures,the phonon electron drag effect will improve the Seebeck coefficient of silicon nanowires and reduce the thermal conductivity,so as to improve the thermoelectric properties of silicon nanowires.Through the tight binding method based on density functional theory,silicon atomic chains with different atoms and silicon nanowires with different widths were simulated to study the structures and electronic properties by analyzing the energy,the distribution function,bond length,bond angle and Mulliken charge aggregation number of nanowires.These calculations can provide us the possibility of using the silicon nano size materials as a carrier find a feasibility method to reduce thermal conductivity,and theoretical reference for controlling preparation of new micro nano thermoelectric devices with more excellent thermoelectric properties.The study found:Silicon atomic chains are symmetric structures.When the atom number of atomic chains is small,they are straight chains.The chains' structures are"Zigzag" as they contain more atoms.With the increase of distance between atoms,there are dimers and trimers in the atomic chains.Charges of silicon atomic chains are symmetric,charges located at the ends of the chains transfer to the inside atoms of atomic chains,a part of charges on the end atoms lost also transfer to the outer end atoms of their neighboring atoms,charges on the atoms in the inner region change less;The atomic structure of the nanowires with different widths exhibits a diversity of dimerization and trimerization rearrangements on the surface of the silicon nanowires after relaxation.With the change of the width,the spatial arrangement of the atoms in the nanowires has different spatial lengths.The cross section of the silicon nanowires shows asymmetric fusiform structure,and the change of the bond length,dimer bond length and bond angle of the nanowires is greatly affected by the size effect.The system size and surface rearrangement of silicon nanowires are important factors to determine the stability of nanowires.The surface charge distribution of silicon nanowires is closely related to the arrangement of atoms on the surface layers.