Electronic properties of defects in pulsed-laser deposition grown ZnO with levels at 300 and 370 meV below the conduction band

We have used deep level transient spectroscopy (DLTS) to characterize defects in ZnO grown by pulsed-laser deposition (PLD). Using high resolution Laplace DLTS, we found that at the high temperature side of the commonly observed defect E3 (about 300 meV below the conduction band) another close lying peak (E3′ with thermal activation energy of 370 meV) is also observed. The concentration ratio of E3 and E3′ depends on the annealing history of the samples. It is most prevalent in as-grown samples and samples that had been annealed in an oxygen atmosphere. This suggests that E3′ may be related to the incorporation of oxygen in the lattice. Electron capture onto that E3′ defect strongly increases with increasing temperature.