Excited-state optical transitions of excitons and biexcitons in a single InxGa1-xAs quantum disk

The photoluminescence of In(x)Gal(1-x)As/A1(x)Ga(1-x)As quantum disks is in vestigated by microscope photoluminescence (PL) and PL excitation spectrosc opies. The excited-state transitions of excitons and biexcitons are studied in terms of their dependence on excitation photon polarization. Their orig ins are analyzed on the basis of symmetry properties expected of excitons a nd biexcitons. Dominant excited-state resonances are ascribed to successive two-step absorptions of two photons of opposite optical orientation, one i nto an exciton excited state followed by another into a densely distributed biexciton excited state. Filling of the exciton state is found to lead to absorption from the exciton ground state to the biexciton excited state. Re maining excitation resonances with large oscillator strength are identified as two-photon absorption processes that directly create weakly correlated exciton pair states. [S0163-1829(98)05147-9].