Browsing by Author "Gebrehiwet, Hagos"

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    Absorption Coefficient and Dielectric function of direct Band Gap silicon Nanocrystallites
    (Addis Ababa University, 2007-07) Gebrehiwet, Hagos
    Silicon is an ubiquitous electronic material and the discovery of strong room temperature luminescence from porous silicon in 1990 raised hopes it may find a new lease of life in the emerging field of optoelectronics. First, the luminescence was shown to be emitted from nanostructures in a porous silicon network. Later the same emission was seen from silicon nanocrystallites and the concept of a silicon quantum dot emerged. A number of different models have been proposed for the origin of the light emission. Some involve interface states between a silicon nanocrystallite and a surrounding shell, while others consider the effect of quantum confinement in an indirect bandgap semiconductor. In order to clarify the influence of morphological properties, such as size or shape, of a silicon nanocrystallite on its optical properties, calculations of optical absorption coefficient and dielectric function of silicon nanocrystallites as a function of effective silicon nanocluster size (diameter) and photon energy were attempted using k.p method. To conclude, the work presented in this thesis gives support to the quantum confinement effect in explaining the optical properties of band gap nano-sized silicon below 10nm, as well as highlighting the importance of calculating optical parameters of silicon nanocrystallites to understand optical properties in the luminescence process