Critical thickness of common-anion II-VI strained layer superlattices (SLSs)

The critical thicknesses of quantum wells in the common-anion superlattices ZnSe-CdSe and ZnS-CdS have been determined experimentally for comparison with calculations. Photoluminescence measurements reveal a large drop in luminescence efficiency when the thickness of CdSe (CdS) wells in a ZnSe (ZnS) lattice exceeds 1.3 nm. Annealing a ZnSe-CdSe SLS in which the well width is slightly in excess of the critical thickness (1.3 nm) causes an increase in luminescence efficiency as the ZnSe and CdSe layers interdiffuse thereby reducing the inter-layer strain: in consequence, misfit dislocations shrink and eventually disappear. These results directly confirm that a dislocation mechanism is responsible for the variation of photoluminescence intensity with well width in ZnSe-CdSe and ZnS-CdS SLSs.