Influence of the growth temperature and annealing on the optical properties of {CdO/ZnO}30 superlattices

The optical properties of short period {CdO/ZnO} superlattices (SLs) grown by plasma assisted molecular epitaxy were analyzed. SLs structures were successfully obtained at various growth temperatures from 360 to 550 °C. Using XRD and SIMS measurements we observed that the growth temperature significantly affects the crystallographic quality of the multilayer structures and, as a rule, the lower growth temperature the better their quality and, in particular, SIMS measurements revealed in-depth oscillations of Cd composition after the growth at 360 °C. Luminescence studies showed that near-band-edge (NBE) luminescence in the UV region dominates in as-grown samples. We found that rapid thermal annealing (RTA) at 900 °C strongly influences the optical properties of these structures. In particular, the NBE emission peaks broaden and redshift towards lower energies in comparison to as-grown structures. Also, various intense defect luminescence bands are detected and their intensities and spectral positions depend on the growth temperature. These results suggest that the SLs degrade during annealing due to intermixing of Zn and Cd atoms and the final defect structure in RTA annealed samples is determined by their initial distribution.