Influences of strain on binding energies of excitons in InAs/GaAs quantum dot molecules

We investigate theoretically strain effects on bonding properties of excitons in both symmetric and asymmetric InAs/GaAs quantum dot molecules (QDMs). The dependences of exciton binding energies on interdot spacings (d) were systematically explored. A critical dot separation dc can be found where the binding energy reaches a minimum value. The decoupling of electron (hole) and the subsequent degeneracy of hole (electron) respectively lead to the minimum and maximum of binding energies in unstrained (strained) QDMs. The strain can significantly tune binding energies of excitons by changing the height of QD in symmetric QDMs. Furthermore, as compared to unstrained systems, strain results in the transition from direct to indirect excitons in asymmetric QDMs. The variation of binding energies in large asymmetric structures is 2 times higher than that in symmetric ones, showing the obvious modulation character by strain in non-symmetric QDMs.