Electrons in coupled vertical quantum dots: Interdot tunneling and Coulomb correlation

Interdot tunneling, lateral confinement, and Coulomb correlation determine how charge is transferred when a bias is applied between the dots in coupled quantum dot systems. The effective-mass Schrödinger equation for interacting electrons confined in coupled vertical double-dot systems is solved to study interdot charge transfer. The configuration-interaction method is used to explicitly include intradot and interdot electron correlation. The energy spectra, charge densities, and correlation functions for interacting two-electron systems in coupled dots are presented as functions of the applied bias between the dots. In small dots with strong lateral confinement, where the Coulomb energies are larger than the interdot tunneling resonances, the total charge on a dot changes in integer jumps as a bias is applied. Lateral correlation is inhibited by strong lateral confinement and charge tunneling out of a dot is uncorrelated to the charge remaining in the dot. The dot charge changes more smoothly with applied bias when the dots are more strongly coupled by interdot tunneling or in larger dots where intradot correlation causes large intradot charge separation, which reduces charging energies and suppresses the Coulomb blockade of charge transfer. In large dots, charge tunneling out of a dot remains strongly correlated to charge left on the dot. To study charging in vertical quantum dot resonant-tunneling structures, the dots must be wide enough that charging energies are large compared to the single-particle-level spacings, but not so large that intradot correlation strongly suppresses the charging energies and Coulomb blockade effects.