| AVS 54th International Symposium | |
| Electronic Materials and Processing | Thursday Sessions |
| Session EM-ThP |
| Session: | Electronic Materials and Processing Poster Session |
| Presenter: | E.H. Khan, Washington State University |
| Authors: | E.H. Khan, Washington State University S.C. Langford, Washington State University J.T. Dickinson, Washington State University |
| Correspondent: | Click to Email |
We report observations of particle and light emission from single crystal and anodic ZnO during pulsed 193-nm irradiation by quadrupole mass selected time-of-flight measurements and photoluminescence spectroscopy. The particle emissions in particular are relevant to thin film production by laser ablation deposition. At fluences between 50 and 600 mJ/cm2, the only ion observed from single crystal ZnO at our level of sensitivity is Zn+. The mean kinetic energy of 3.3 ± 1.6 eV is consistent with electrostatic ejection from defect sites with a net positive charge. Zinc ions absorbed on top of surface electron traps would experience a repulsive force when the underlying trap is photoionized. During prolonged irradiation, the Zn+ intensity drops quickly, reflecting the depletion of surface defects by the emission process. Consistent with the radiation hardness of ZnO, single crystal remains transparent during prolonged irradiation. However, the sample photoluminescence evolves from greenish-blue, to deep blue, and to violet. At fluences above 600 mJ/cm2, the Zn+ intensities increase rapidly and other positive ions appear, including O+ and O2+. Neutral O and O2 appear, followed by neutral Zn at 775 mJ/cm2. Analyses of the neutral time-of-flight distributions indicate effective surface temperatures near 600 K at 800 mJ/cm2 and near 1100 K at 1.2 J/cm2. These temperatures are well below the melting point of ZnO, suggesting that the observed neutral species are produced photochemically and desorb thermally. At these fluences, intense ion emissions persist for many thousands of laser pulses; defects consumed in the emission process are continuously replenished. Emissions from anodic black ZnO are similar to the emissions from single crystals except that comparable emission intensities are achieved at lower fluences for the black ZnO. Weak emissions are also observed from the native oxide on electropolished Zn plate.
1We thank Dr. L. Boatner of Oak Ridge National Laboratory for providing single crystal ZnO. This work is supported by the DOE grant DE-G03-02ER45988.