A Tight Binding Study of Strain-Reduced Confinement Potentials in Identical and Non-Identical InAs/GaAs Vertically Stacked Quantum Dots

Strain and electronic structure of InAs/GaAs quantum dot molecules made up of identical and non-identical vertically stacked quantum dots are compared using the sp³d⁵s* nearest neighbor empirical tight binding model. Hydrostatic and biaxial strain profiles strongly impact the local band edges and electronic structure for both identical and non-identical dots. Strain in the lower dot is significantly different as compared to the upper dot in the non-identical system in contrast to the identical system where it is almost the same in both dots. Therefore structural detailed differences are of critical importance and cannot be neglected. Qualitatively, the electronic structure is similar in identical and non-identical dot systems for small separations (below 6 nm) and it is significantly different for large separations. The molecular orbitals convert to the dot-localized atomic orbitals at large dot separations in the non-identical system. Non-idealities such as strain and size variations induce an energy splitting in the considered dot ground states. Larger dissimilarity of dots increases e1-e2 and decreases the optical gap of system. This favors the possible use of such system in the construction of the long wavelength optical laser.