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This letter reports the successful growth of short period (ZnSe)4/CdSe4 strained layer superlattices on (100) GaAs surface by atomic layer epitaxy. The superlattice was characterized by x-ray diffraction and Raman scattering. Superlattice period was calculated from the satellite peaks and was in good agreement with the expected value. 2LO Raman scattering in resonance with the E1h exciton level was observed. Experimental exciton energy was compared with the one calculated in a finite-square-well model. A Raman line due to stimulated Raman scattering was also observed.

TOand LO-modes of PbSel-,Te, mixed crystals are determined from optical measurements in the frequency range 660 to 10 cm-l a t 300, 100, and 8 K. The results for polycrystalline bulk samples as well as for thin films, prepared by hot-wall epitaxy, show a two-mode behaviour. This conclusion is in contrast to a number of criteria which permit a prediction of the mode behaviour.Aus optischen Messungen im Spektralbereich 660 bis 10 em-1 bei 300, 100 und 8 K werden die TOund LO-Moden der Mischkristallreihe PbSel -%Te, ermittelt. Die Ergebnisse sowohl fur polykristalline Massivproben als auch fur dunne, durch hot-wall-Epitaxie hergestellte Schichten deuten auf ein Zwei-Moden-Verhalten. Diese Folgerung steht im Widerspruch zu den Voraussagen einiger Kriterien, die das Modenverhalten charakterisieren.