On the formation and nature of nanometer size clusters on the surface of ZnSe epilayers

Abstract

ZnSe epilayers were grown on GaAs (001) substrates by metal organic chemical vapor phase deposition, using different group VI–II precursor flow ratios. Atomic force microscopy (AFM) examinations of their surface show that epilayers grown with a high VI/II ratio are not as stable as those grown with a low ratio. When exposed to air, Se clusters would appear and grow on the surface of the unstable epilayers. The ripening process could take as long as 50 days at room temperature. Secondary electron and cathodoluminescence images indicate that the clusters are more likely to emerge from areas of high defect density. Moreover, AFM topographic images of epilayers at an intermediate stage of ripening suggest that clusters near surface depressions would grow in size at the expense of others. By using a low accelerating voltage and allowing the clusters to grow to a size larger than the electron interaction volume, we used energy dispersive x-ray analysis to show that the clusters are made up entirely of Se.