Identification of oxygen and zinc vacancy optical signals in ZnO

Photoluminescence spectroscopy has been used to study single crystalline ZnO samples systematically annealed in inert, Zn-rich and O-rich atmospheres. A striking correlation is observed between the choice of annealing ambient and the position of the deep band emission (DBE) often detected in ZnO. In particular, annealing in O-2 results in a DBE at 2.35 +/- 0.05 eV, whereas annealing in the presence of metallic Zn results in DBE at 2.53 +/- 0.05 eV. The authors attribute the former band to zinc vacancy (V-Zn) related defects and the latter to oxygen vacancy (V-O) related defects. Additional confirmation for the V-O and V-Zn peak identification comes from the observation that the effect is reversible when O- and Zn-rich annealing conditions are switched. After annealing in the presence of ZnO powder, there is no indication for the V-Zn- or V-O-related bands, but the authors observe a low intensity yellow luminescence band peaking at 2.17 eV, probably related to Li, a common impurity in hydrothermally grown ZnO. (c) 2006 American Institute of Physics.