Electronic states in Si quantum dots are theoretically examined, taking account of a multivalley structure of conduction band. Using the effective mass approximation, we find that one-electron levels in different valleys are degenerate when the confinement potential is smooth. The exchange interaction between different valleys is negligibly small, which results in the degeneracy of different spin states. In the presence of intervalley scattering, caused by e.g. impurities within the dot, sharp edge of the confinement potential, the degenerate one-electron levels are split and the lowest spin state is realized. To confirm the validity of the effective mass approximation, we calculate the electronic states in an empirical tight-binding model, considering the atomic structure in Si quantum dots.
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