  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.
