GAIN STUDIES OF (CD, ZN)SE QUANTUM ISLANDS IN A ZNSE MATRIX

By inserting stacked sheets of nominally 0.7 monolayer CdSe into a ZnS e matrix we create a region with strong resonant excitonic absorption. This leads to an enhancement of the refractive index on the low-energ y side of the absorption peak, Efficient waveguiding can thus be achie ved without increasing the average refractive index of the active laye r with respect to the cladding. Processed high-resolution transmission electron microscopy images show that the CdSe insertions form Cd-rich two-dimensional (Cd, Zn)Se islands with lateral sizes of about 5 nm. The islands act as quantum dots with a three-dimensional confinement f or excitons. Zero-phonon gain is observed in the spectral range of exc itonic and biexcitonic waveguiding. At high excitation densities excit onic gain is suppressed due to the population of the quantum dots with biexcitons. (C) 1998 American Institute of Physics.