Y-Line Emission and Lattice Relaxation in MBE-ZnSe and -ZnSSe on GaAs

The Y-line emission in photoluminescence spectra at 11 K was studied in MBE-ZnSe and -ZnSSe (up to a sulfur content x=0.13) on GaAs. Compared with X-ray diffraction data, the Y-line seems to relate to misfit dislocations, and thus seems a good measure for checking lattice relaxation in ZnSe and ZnSSe epilayers with a sulfur content x<0.04. The critical thickness h c determined from the Y-line is compared with the theoretical predictions of Matthews and Blakeslee. No Y-line was observed for sulfur content x>0.05, the reasons for which are discussed.