First-principles Study Of The Modulation Of Optical And Electronic Properties Of Low-dimensional Silicon Nanostructures

Silicon, the basis of modern semiconductor industry of modern, is anirreplaceable role in many fields, especially computer manufacturing. As Moore’sLaw is about to come to an end, people began looking for new materials to sustainMoore’s Law. In recent year, a variety of low-dimensional materials have been foundor successfully prepared, setting off a boom in the field of nanotechnology research.Nanomaterials exhibit many novel physical and chemical properties, which could beapplied for next gerenation nanodevices, due to restrictions on the dimension ofnanomaterials. And low-dimensional systems of silicon material are perfectlycompatible with modern technology of silicon, so it is very important to studyphysical and chemical properties of silicon lower-dimensional nanosreuctures. Basedon first-principles density-functional theory calculations, we studied systematicallydoping and surface functionalization effect on one-dimensional and two-dimensionalsilicon nanostructures, and the microscope mechanism of the effects were illustratedin this thesis, the main results are as follows:1. The impact of vacancy defect on the doping of silicon nanowires issystematically studied by the first-principles calculations. The atomic structuresand electronic properties of vacancies and vacancy-boron (vacancy-phosphor)complexes in H-passivated silicon nanowire with diameter of2.3nm areinvestigated. The results of geometry optimization indicate that a centralvacancy can exist stably, while the vacancy at the edge of nanowire undergoes alocal surface reconstruction which results in the extradition of vacancy out ofnanowire. Total-energy calculations indicate that central vacancy tends to formvacancy-dopant defect pair. The further analysis shows that n-type dopingefficiency is strongly inhibited by the unintentional vacancy defect. In contrast, the vacancy defect has little effect on p-type doping. Our results suggest that thevacancy defect should be avoided during the growth and the fabrication ofdevices.2. First-principles calculations are employed to investigate total energies andelectronic structures of the B/P doped silicon nanowires, the B/P doped siliconnanowires with and without dangling bond (DB). And the calculation indicatesthat the DB would lead to the lowering doping efficiency. Moreover, the smallmolecule adsorption can reactivate impurities doping p/n characteristics. It isimportant that the effect of molecular passivation on doping silicon nanowiremaintain p/n charactistics.3. The size and stacking effects on the structural, electronic, and optical properties ofhydrogenated few-layer silicenes (HFLSs) are systematically investigated. It isfound that both the formation energies and band gaps of HFLSs increases with thereduction of layer thickness. The high formation energies imply the relativelylower structural stability in the thinner HFLSs due to their high surface/volumeratio. As the layer thickness decreases, the increasing band gaps lead to anobvious blue shift of optical absorption edge in the HFLSs. Among three differentstacking HFLSs with the same thickness, the ABC-stacking one has the lowestformation energy and the largest band gap due to the strong interactions of Silayers. The difference of stacking modes induces a relative blue shift of opticalabsorption peaks in the ABC-stacking HFLS compared to the AA-stacking one.The results indicate that the electronic and optical properties of HFLSs stronglydepend on their size and stacking modes.