Morphology of ultrathin CdSe quantum confinement layers in ZnSe matrices

Using a combination of transmission electron microscopy (TEM), high resolution TEM (HRTEM), digital analysis of lattice images (DALI), and correspondence analysis (CA) we present at near-atomic resolution the morphology of a nominal 2 monolayer (ML) cadmium selenide (CdSe) quantum well (QW) between ZnSe barriers. We reveal the presence of approximately 10 ML zinc cadmium selenide (Zn_xCd_1-xSe) alloy insertion layer of varying composition in a ZnSe matrix. A spotty pattern in the plane of the layer indicates the presence of self-assembled clusters or islands similar to the structures commonly referred to as quantum dots. Further analysis indicates that these clusters, of less than 10 nm in lateral extent, themselves contain sites highly saturated with CdSe. Analysis of photoluminescence (PL) spectra suggests that the emission originates predominantly from excitons trapped in these islands.