Cathodoluminescence characterization of hydrothermal ZnO crystals

Hydrothermal ZnO crystals were grown using 3N NaOH, 1N KOH and 0.5N Li2CO3 alkali solvents. The crystals have been studied by means of cathodoluminescence (CL), revealing high crystalline quality. The different growth sectors are identified by CL imaging. The incorporation of impurities and non-radiative recombination centers depends on the growth sector. The surface introduces band tailing producing self-absorption of the high energy luminescence photons. The broad visible luminescence band is composed of at least three different bands, green, orange and red, which are non-equally distributed, depending on the growth sector. Also a strong dependence of the visible luminescence on the penetration depth of the excitation - the e beam - is observed, which suggests that the concentration of the deep levels responsible for the visible luminescence is at the sample surface to a depth of 2 μm.