| AVS 56th International Symposium & Exhibition | |
| Electronic Materials and Processing | Thursday Sessions |
| Session EM-ThM |
| Session: | Oxide Semiconductors |
| Presenter: | E. Kahn, Washington State University |
| Authors: | E. Kahn, Washington State University S. Langford, Washington State University T. Dickinson, Washington State University |
| Correspondent: | Click to Email |
Many dielectric crystals color in the visible region of the spectrum under intense ultraviolet light such as excimer laser irradiation. We have shown previously that in many cases these are due to electron hole pair production via two photon absorption. Examples are coloration of alkali halides and alkaline earth halides where self=trapped excitons lead to formation of strongly absorbing defects. Recently we were surprised to see dramatic coloration of single crystal ZnO, a wide bandgap (3.37 eV) semiconductor of significant technological interest, under exposure to 193 nm ArF excimer laser radiation. The increase in absorption is very broadband, extending from the bandgap into the infrared, appearing as near black to grey. We present careful measurements of the properties of this coloration and determine its origin. We present convincing evidence that it is due to the formation of zinc metal nanoparticles residing on the surface of the irradiated region. This evidence involves AES, TEM, XRD, UV-VIS reflection and absorption spectroscopy as well as Positron Annihilation Spectroscopy. As expected, laser fluence has considerable impact on the size, number, and spatial distribution of these nanoparticles. We present a model for the production of this Zn metal rich surface and discuss applications including plasmonics. Related optical property measurement will be presented. Furthermore, we show that with suitable choices of laser exposure we are able to convert the originally n-type ZnO to p-type. We are carrying out additional experiments to confirm that this transformation is dependent on the formation of O-vacancies. Supportive UHV mass spectroscopy measurements of the emitted particles during laser exposure show copious release of atomic and molecular oxygen suggesting O depletion is occurring.
This work was supported by the U.S. Department of Energy, DE-FG02-04ER-15618