Effects of KrF (248 nm) excimer laser irradiation on structural and optical properties of ZnO single crystal

The properties of ZnO single crystals irradiated by a pulsed 248 nm excimer laser have been systematically studied by XRD, PL and Raman measurements. It was observed that the surface roughness and the magnitude of the grain size on the surface of the irradiated ZnO crystals became larger, as well as their band-edge emissions at room temperature were found to become weaker and shift to higher frequency with increasing laser energy densities. Green luminescence emission has a contrary trend. Our Raman results show that bulk properties of the irradiated ZnO crystal diminish but the defect-, surface-related features display as laser energy densities increases. The Raman spectra of the irradiated ZnO crystals are deteriorated bulk spectra with spectroscopic line broadening and merging, line intensity is reducing, and position shifting, because the laser irradiation onto the surface of ZnO crystal leads to the thermal decomposition of ZnO into metallic Zn and oxygen gas and the increase of oxygen vacancies or interstitial Zn atoms. A new phonon around 568cm⁻¹ related to interstitial Zn atoms in the irradiated ZnO crystal was observed. These results are associated with micro-structure variation of ZnO single crystals caused by laser irradiation.