Cathodoluminescence characterization of ZnO tetrapod structures

Spatially resolved cathodoluminescence (CL) measurements are performed to characterize optical properties and structural quality of ZnO tetrapods. High optical quality of these structures is concluded based on the observation of intense free excitonic (FE) emission at room temperature and a low intensity of the so-called green emission of defect origin. CL mapping performed for individual tetrapods has revealed that the defects responsible for the green emission are predominantly located in core regions (i.e. close to leg junctions) and, therefore, are unlikely to reside near surfaces. Variations in the spectral positions of the FE emission monitored in tetrapod legs of different diameters are also observed and are attributed to the formation of whispering gallery mode polaritons within the tapered microcavity.