Optical characterization of periodically polarity-inverted ZnO structures on (0001) Al2O3 substrates

We investigated the optical properties of periodically polarity-inverted (PPI) ZnO structures formed on (0001) Al2O3 substrates by evaluating the cathodoluminescence (CL) as a function of the acceleration voltage (Vacc). At surface regions with a low Vacc, the emission from the interface region was dominant but the dominant emission source changed to the Zn-polar regions as Vacc was increased, which can be explained by the different exciton diffusion lengths. The dependence of the emission properties on Vacc showed a slight red shift as Vacc increased and a larger red shift was observed in the Zn-polar regions. Moreover, the interface regions showed the highest intensity compared to other regions, which can be explained by the results of the geometrical analysis conducted using a finite-differential time domain simulation.