  Using single-particle pseudopotential and many-particle configuration
interaction methods, we compare various physical quantities of (In,Ga)As/GaAs
quantum dot molecules (QDMs) made of dissimilar dots (heteropolar QDMs) with
QDMs made of identical dots (homopolar QDMs). The calculations show that the
electronic structures of hetero-QDMs and homo-QDMs differ significantly at
large inter-dot distance. In particular (i) Unlike those of homo-QDMs, the
single-particle molecular orbitals of hetero-QDMs convert to dot localized
orbitals at large inter-dot distance. (ii) Consequently, in a hetero-QMD the
bonding-antibonding splitting of molecular orbitals at large inter-dot distance
is significantly larger than the electron hopping energy whereas for homo-QDM,
the bonding-antibonding splitting is very similar to the hopping energy. (iii)
The asymmetry of the QDM increases significantly the double occupation for the
two-electron ground states, and therefore affects the degree of entanglement of
the two electrons.
