Optical properties of self-assembled II-VI quantum dots

We discuss optical properties of self-assembled CdSe-based quantum dots (QDs) studied by photoluminescence (PL), selective PL, PL excitation, and magneto-PL in our laboratory as well as by other groups. Our own QD specimens were fabricated by depositing approximately 3 monolayers of CdSe on ZnSe using MBE. Samples consisting of capped QDs showed intense excitonic transitions from the QD ensemble. The PL spectra were strongly inhomogeneously broadened, but survived to relatively high temperatures without further broadening of the PL line. Selective PL showed clear LO- phonon resonances which - together with the observed temperature stability of the PL band - clearly indicate that the broad band is a superposition of atomic-like spectra emitted by strongly localized excitons. In addition to CdSe QDs on ZnSe, we also studied magneto-PL of QD systems involving diluted magnetic semiconductors (DMSs), in an attempt to determine the degree of exciton localization in the dots. While these experiments are still inconclusive, the results - and particularly the observation of a dramatic magnetic-field-induced enhancement of PL intensity in DMS based systems - are extremely interesting in their own right, and will also be discussed.