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We present studies of the excitonic spectrum in superlattices (SLs) of CdSe insertions in a ZnSe matrix aimed at elucidating the CdSe/ZnSe interface morphology. The experimental photoluminescence excitation spectra are compared with the results of variational exciton calculations performed within the effective mass approximation. The shape of the average vertical (along the SL growth axis) distribution of CdSe within each insertion, used in the calculations, was obtained from a theoretical simulation of X-ray diffraction (XRD) rocking curves measured in the same samples. The results indicate that the thinnest layers are graded composition ZnCdSe quantum wells (QWs), generally homogeneous in the layer planes, whereas flat islands enriched by Cd appear at the CdSe nominal thickness larger than 0.5-0.6 monolayer (ML).

Double and triple X-ray diffractomery was used for a structural characterization of the short-period superlattices (SLs) CdSe/ZnSe with submonolayer sheets of CdSe. The multilayer structures containing SLs were grown by molecular beam epitaxy (MBE) on (001) GaAs substrates. The period of SLs was in range (30–60 A), the nominal thickness of CdSe sheets varied from 0.2 to 1.2 monolayer. The parameters of SLs have been determined. Broadening of CdSe sheets in direction normal to interface has been revealed. Full width at half maximum (FWHM) of this broadening is equal to about 4.5 monolayers and does not depend on the period and content of Cd in SLs.