Theory of Dynamical Processes in Semiconductor Quantum Dots

Abstract

The focus of this dissertation is on the theory of the electronic dynamical processes in semiconductor quantum dots (QDs). The first part of the dissertation introduces the calculation method of electronic eigenstates used through the dissertation, the sp3s* tight-binding (TB) method, and the application of the symmetry-adapted linear combination (SALC) of atomic orbitals to the TB method. The combination of the SALC and TB method reduces the computational load, and generates reliable electronic eigenstates and eigenvalues of Wurtzite CdSe QDs. The second part of the dissertation uses the calculated eigenstates and eigenvalues of CdSe QDs, whose band gap states are removed by a passivation layer, to calculate various kinds of physical properties, such as the structure, the permanent dipole moment, the band gap, the molecular orbitals, the density of states (DOS), and the absorption spectrum. These calculated results are compared with the respective experimental measurements in further discussions. The last part of the dissertation focuses on the studies of the size-dependent trend of the Auger electron-hole recombination process that causes the semiconductor QDs to remain in the dark state, including the cases of a negative trion, a positive trion, and a biexciton, in semiconductor QDs. The rates of these Auger processes are expressed in the form of Fermi’s golden rule, where the Coulombic interaction between the two electrons is the operator. Although the calculated results shows larger size dependence than that of the experimental findings, the literature of recent experiments and theories points out potential remedies to the discrepancy by modifying the current computational setting and theory in the dissertation.