We have investigated the effect of upper barrier layer growth on self-assembled CdSe quantum dots (QDs) by transmission electron microscope (TEM) and atomic force microscope (AFM). The AFM image of CdSe surfaces reveals a lot of isolated CdSe dots and non-uniform two-dimensional, CdSe islands. The alloying layer is observed by cross-sectional TEM image, This alloying is explained by the diffusion of CdSe when ZnSe cap layer is grown on CdSc surfaces. Photoluminescence excitation spectra of self-assembled CdSe QDs reveal the existence of a non-uniform CdZnSe quantum well and CdSe QDs with CdZnSe alloy region. This result is in good agreement with the results of TEM and AFM observations.