Browsing by Author "Kelil, Seyfan"

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    Charge Transport Properties in Disordered Organic Semiconductors Monte Carlo Simulation
    (Addis Ababa University, 2021-06-03) Kelil, Seyfan; Demmeyu, Lemi (PhD)
    In this thesis, we have used a Monte Carlo simulation technique to study the charge carrier mobility as a function of charge carrier density and electric _eld in disordered organic semiconducting materials using the lattice model. Our simulations reveal that the charge carrier mobility versus charge carrier density at lower charge carrier density and disorder is constant. In contrast, at higher disordered and lower charge carrier density, the charge carrier mobility increases with charge carrier density. Therefore, the e_ect of the disorder parameter (^_ = _ kBT ) on the charge carrier mobility is more pronounced than the charge carrier density at lower charge carrier density. We studied a charge carrier mobility as a function of the electric _eld for the case of the regular grid and spatial disorder lattice site with di_erent lattice site spacing parameter r and the ratio of localization length to the lattice parameter (i. e, _=b). We show that a charge carrier mobility increases with an electric _eld for the case of the regular grid and spatial disorder lattice site of lower or equal values of lattice site spacing r to the ratio of _=b. But, at a higher value of lattice site spacing r to the ratio of _=b, the electric _eld dependence of charge carrier mobility for spatial disordered lattice sites di_ers from that of the regular grid case. We observed that both a localization length and lattice parameter are relevant for the electric _eld variation of charge carrier mobility in both the regular grid and spatial disordered lattice sites at lower or equal values of lattice site spacing r to the ratio of _=b cases. However, at higher values of the lattice site spacing r relative to the ratio of _=b, the only parameter responsible for the electric _eld dependence of charge carrier mobility is the localization length of disordered organic semiconducting materials.
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    Nanophotonics for 21st Century: From Fabrication to Application
    (Addis Ababa University, 2010-06) Kelil, Seyfan
    This project work gives a panoramic view of the past activities, present development and future directions with multi-facets application possibilities of nanophotonics. Nanophotonics is a new paradigm of nanoscience for 21st century, which deals with optical processes at the much smaller length scale than the wavelength of optical radiation. The nanoscale matter-radiation interaction includes nanoscale confinement of radiation, nanoscale confinement of matter, and nanoscale photo-physical or photochemical transformation, offer numerous opportunities for both fundamental research and technological applications. Two main broad areas of Nanophotonics are Surface Plasmonics and Photonic Crystal. Surface Plasmonics are collective charge oscillations that occur at the interface between conductors and dielectrics. Plasmonic devices have already shown to be excellent candidates for a number of different optical applications. Photonic Crystals are artificial periodic structures whose dielectric constant is periodically modulated in the order of light wave length, which can create arrange of forbidden frequencies called a Photonic band gap (PBG). In Photonic Crystal structures, the band structures ideas of solid state physics are applied to electromagnetic wave. Here we present mainly the physics of nanophotonics, challenges in fabrications and many applications. This paper concludes with the future of nanophotonics, seems bright and close to reality. This field is expected to revolutionize many aspects of modern life. We start with a brief introduction and then elaborate the physics behind it. The application areas are, however, wide spread and in every field of Science and Technology