Effect of thermal annealing on Cu-related green luminescence in ZnO

We have studied the effects of thermal annealing in air on photoluminescence of bulk ZnO crystals grown by hydrothermal technique and nominally undoped ZnO layers grown by molecular beam epitaxy on sapphire. Annealing of the samples in air at temperatures above 600°C resulted in a dramatic enhancement of the Cu -related green luminescence (GL) band peaking at 2.45 eV and having characteristic fine structure. The GL band quenched at temperatures above 300 K due to escape of holes from the excited state of the Cu Zn acceptor to the valence band. SIMS profiles revealed moderate increase of Al concentration and significant increase of Cu concentration in annealed samples. Exciton bound to hydrogen-related donor (the 3.363 eV line) quenched after annealing the sample at temperatures above 750oC.