Single fractional monolayer (FM) CdSe/ZnSe structures have been grown by molecular beam epitaxy (MBE), employing both conventional MBE and migration-enhanced epitaxy (MEE). A precise calibration of the FM mean thickness in the range of 0.15–3.0 ML has been performed for both techniques, revealing more than a 3.5 times lower Cd incorporation ability for the MEE mode at the same Cd and Se incident fluxes. Steady-state and time-resolved photoluminescence spectroscopy is used to characterize the intrinsic morphology of the CdSe FMs, with a special emphasis on the submonolayer thickness range. Both MBE and MEE grown samples exhibit inhomogeneity of the excitonic system, which can be explained by coexistence of a homogeneous alloylike layer and relatively large CdSe 2D clusters. The MEE samples display smaller fluctuations of the layer thickness and island sizes. © 1998 American Institute of Physics.