Browsing by Author "Alemgasha, Girma"

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    Zero Phonon and Phonon Assisted Radiative Transition Rates Based on Finite Potential well Approximation for Silicon Nanocrystallite Embedded in Silicon Oxide
    (Addis Ababa University, 2009-06) Alemgasha, Girma; Goshal, Sib Krishna (PhD)
    The purpose of this thesis was to study phonon assisted and zero phonon radiative lifetimes of electron-hole pair which are excited and recombine inside nc-Si, on the basis of more realistic assumption of finite potential well and envelope wave approximations for oxidized PS and nc-Si inside SiO2. Finite potential well approximation results the spread of conduction and valence band edge wave functions in to SiO2. Solving time independent Schr¨odinger equation in the two materials and applying matching boundary condition at the interface for envelope wave function part; we found bandgap energy closer to experimental results that increase at lower rate as we shrink the size of nc-Si compared to infinitely deep potential well approximation. Radiative rates for both zero phonon and phonon assisted transitions are calculated with the newly developed wave functions and by separately calculating momentum overlap factor and incorporating it into momentum matrix elements by hand. New radiative lifetime estimation in the order of nanosecond for nc-Si size below 2 nm is found. We also found μs order of life time for phonon assisted recombination rate below 2 nm size of nc-Si. However, the value we got for phonon assisted radiative transition rate does not show any significant difference from infinitely deep potential well approximation results