Optical, structural and lattice dynamical properties of epitaxial Zn1-yMgySxSe1-x layers grown by metalorganic vapour phase epitaxy

The optical, structural and lattice dynamical properties of Zn1-yMgySxSe1-x epilayers grown by low pressure metalorganic vapour phase epitaxy were investigated. The composition of these layers, determined by electron probe microanalysis, was varied in the range of 0 less than or equal to x, y less than or equal to 0.2. Photoluminescence measurements in the temperature range between 14 and 300 K were performed. The alloy broadening of the bandedge emission depending on the composition of the layer was calculated on the basis of a binomial statistical model. The comparison between the measured bandedge photoluminescence halfwidth and the calculated alloy broadening showed high composition homogeneity for samples with low sulphur and magnesium contents (x, y 0.16) and poor homogeneity for samples with large x and y. Scanning transmission electron microscopy investigations showed a low density of structural defects in samples with narrow bandedge emission and low x and y, whereas a high defect density was detected in samples with large bandedge broadening. These results are correlated to the observation of symmetric and asymmetric profile shapes of the broadened X-ray rocking curves, respectively. Four-mode behaviour of the ZnMgSSe lattice vibrations was testified by Raman measurements.