Anisotropic enhancement of piezoelectricity in the optical properties of laterally coupled InAs/GaAs self-assembled quantum dots

Abstract

We investigated the electronic and optical properties of self-assembled laterally double InAs/GaAs quantum dots coupled along the [110] and $[1\overline{1}0]$ directions with varying interdot distances. The coupling region provides a stronger confinement for both electrons and holes than in the center of each dot due to the weak compressive strain and positive biaxial strain in the region. The lateral coupling along the [110] $([1\overline{1}0])$ direction enhances the negative (positive) piezoelectric potential in the coupling region and lowers (raises) the potential in the middle of each dot. As a result, the piezoelectric potential decreases the splitting between the two transitions from the bonding $s$ orbitals to the two coupled $p$ orbitals in quantum dots coupled along the $[1\overline{1}0]$ direction and increases the splitting in the quantum dots coupled along the [110] direction. The direction of coupling is clearly distinguishable by the polarization of intraband transition since most transitions are polarized along the axis passing through the two dots. Lateral coupling enhances the polarization anisotropy of interband absorption spectra. In the presence of the piezoelectric potential, quantum dots coupled along the [110] direction exhibit larger redshift of the lowest exciton energies when the distance between the two dots is sufficiently close and have smaller exciton binding energies than quantum dots coupled along the $[1\overline{1}0]$ direction.