  Using resonantly excited photoluminescence along with photoluminescence
excitation spectroscopies, we study the carrier excitation processes in
CdTe/ZnTe and CdSe/ZnSe self-assembled quantum dots. Photoluminescence
excitation spectra of single CdTe quantum dots reflect two major mechanisms for
carrier excitation: The first, associated with the presence of sharp and
intense lines in the spectrum, is a direct excited state ? ground state
transition. The second, associated with the appearance of up to four much
broader excitation lines, is a LO phonon-assisted absorption directly into the
quantum dot ground states. LO phonons with energies of both quantum dots and
ZnTe barrier material are identified in the photoluminescence excitation
spectra. Resonantly excited PL measurements for the dot ensemble as a function
of excitation energy makes it possible to separate the contributions of these
two mechanisms. We find that for CdTe quantum dots the distribution of excited
states coupled to the ground states reflects the energy distribution of the
quantum dot emission, but shifted up in energy by 100 meV. This large splitting
between excited and ground states in CdTe quantum dots suggests strong spatial
confinement. In contrast, the LO phonon-assisted absorption shows significant
size selectivity. In the case of CdTe dots the exciton-LO phonon coupling is
strongly enhanced for smaller-sized dots which have higher emission energies.
In contrast, for CdSe quantum dots the exciton-LO phonon coupling is uniform
over the ensemble ? that is, the energy distribution determines the intensities
of LO phonon replicas. We show that for CdTe quantum dots after annealing, that
is after an increase in the average dot size, the exciton-LO phonon interaction
reflects the dot energy distribution, as observed for CdSe quantum dots.
