Parity symmetry and energy spectrum of excitons in coupled self-assembled quantum dots

A theoretical study is presented for excitons in coupled self-assembled InGaAs quantum dots. We have proposed a model of an isolated single quantum dot based on the assumption of the Gaussian distribution of indium concentration. The same distribution, with the parameters fixed for the single dot, has been applied to vertically stacked coupled quantum dots in order to study the exciton properties, which result from the interdot coupling. The exciton lowest-energy levels have been calculated with use of the many-element variational basis, which includes the two-particle correlation effects. We have discussed the symmetry with respect to the parity of the exciton wave functions in the coupled quantum dots. We have shown that—in a general case—these wave functions do not possess the definite one-particle parity. Only for very small interdot distance the ground-state wave function exhibits the approximate one-particle parity. The nature of splitting of the photoluminescence lines in the coupled quantum dots is discussed. The present theory applied to a description of photoluminescence spectra in coupled self-assembled InGaAs quantum dots leads to a very good agreement with the experimental data.