Thermal annealing studies of the deep level emission in solution-grown zinc oxide nanorods

In this report, the effects of thermal annealing on the room temperature (RT) photoluminescence characteristics of solution-grown ZnO nanorods (ZNs) are presented. It is shown that the near surface regions of as-grown ZNs are rich in Zn. Within the detection limit of X-ray photoelectron spectroscopy (XPS), it is confirmed that the environment of annealing affects indeed the activation of intrinsic defects. Furthermore, thermal treatment at high temperatures removes H-related defects as expected; and this removal process is found to affect significantly the RT luminescence properties of ZNs, especially when ZNs are annealed sequentially from 300 °C to ~700 °C. Specifically, the passivation of vacancy-related defects by H is demonstrated following thermal treatment in this temperature range. Finally, the green luminescence (~500 nm) that evolves following annealing above ~800 °C is assigned to Zn vacancy defects.