Calculation of conduction-to-conduction and valence-to-valence transitions between bound states in (In,Ga)As/GaAs quantum dots

We have calculated the conduction-to-conduction and valence-to-valence absorption spectrum of bound states in (In,Ga)As/GaAs quantum dots charged with up to three electrons or holes. Several features emerge: (i) In pure (non-alloyed) InAs/GaAs dots, the 1S-1P_1 and 1S-1P_2 conduction intraband transitions are fully in-plane polarized along [1\bar 10] and [110], respectively, while valence transitions are weakly polarized because the hole P states do not show any in-plane preferential orientation. (ii) In alloyed In_{0.6}Ga_{0.4}As/GaAs dots the [110] and [1\bar 10] polarization of the corresponding 1S-1P conduction intraband transitions is weakened since the two 1P states are mixed by alloy fluctuations. The polarization of valence intraband transitions is insensitive to changes in alloy fluctuations. (iii) For light polarized along [001], we find a strong valence-to-valence transition that involves a weakly confined hole state with predominant light-hole character. (iv) When charging the dots with a few electrons, the conduction intraband transitions display spectroscopic shifts of ~1-2 meV. These shifts are a result of correlation effects (captured by configuration-interaction) and not well described within the Hartree-Fock approximation. (v) When charging the dots with holes, valence intraband spectra are more complex than the conduction intraband spectra as hole states are strongly affected by spin-orbit coupling, and configuration mixing is more pronounced. Spectroscopic shifts can no longer be identified unambiguously. These predictions could be tested in single-dot spectroscopy of n-doped and p-doped quantum dots.