Voltage-tunable quantum dots on silicon

Employing electrostatic confinement with a dual-gate device we realize periodic arrays of electron dots on Si widely tunable in diameter and electron number. From far-infrared transmission studies of dimensional resonances, we deduce dot diameters down to 40 nm for as little as 20 electrons in quantum states spaced by more than 5 meV. Excitation energies as well as mode dispersions in finite magnetic fields are found to strongly depend on the strength and the shape of the lateral confining potential. A detailed analysis of the oscillator strengths indicates a direct effect of strong quantum confinement.