Evolution of deep electronic states in ZnO during heat treatment in oxygen- and zinc-rich ambients

摘要

Hydrothermally grown ZnO samples have been annealed in Ar, Zn-rich, and O-rich ambients and investigated by deep level transient spectroscopy (DLTS). The DLTS measurements reveal up to 6 different defect levels in the band gap after different annealing conditions. A clear correlation has been found between the annealing treatment and the formation/suppression of two deep defect levels at ～0.2 and ～0.5 eV below the conduction band edge (E_c). As a result, the E_c- 0.5 eV level is assigned to a Zn-rich defect while the E_c- 0.2 eV level is due to a O-rich defect, where the latter shows donor behavior as revealed by a distinct Poole-Frenkel effect.