Size and shape dependence of electronic states in silicon quantum dots

We theoretically examine electronic states in Si quantum dots fabricated by an oxidation technique, considering a multivalley structure of conduction band. In spherical dots smaller than about 10 nm, oneelectron energy levels in equivalent valleys are filled consecutively with increasing the number of electrons N. Owing to the absence of intervalley spin-coupling, high-spin states are realized more often in small magnetic fields, than in GaAs quantum dots. In much larger dots, electrons are accommodated in a valley, making the highest spin of S_tot = N/2, to gain the exchange energy. In elliptical quantum dots, electrons tend to be populated in the elongated direction and make high-spin states.