Cathodoluminescence study of visible luminescence in hydrothermal ZnO crystals

We present a study of the visible luminescence in ZnO hydrothermal crystals. The study is carried out on oxygen polarity basal plane (000-1) plates that are sliced through several distinct growth sectors of the crystal. The plates reveal three distinct regions that display differences in the luminescence emission, especially in the visible range. These differences should be related to the variation in the distribution of impurities and native defects in the various growth sectors of hydrothermal ZnO. CL images also expose the presence of nonradiative recombination centers that are associated with point defects or complexes of point defects. CL measurements varying the acceleration voltage of the e-beam reveal that the deep levels responsible for the green luminescence, and in a minor extension those responsible for the yellow-orange luminescence are depleted near the surface. A discussion about the main hypothesis accounting for such behavior is presented.