Abstract:
Very recently, there has been a rapidly increasing effort for investigating nonlinear optical properties of ZnO while intensive studies have been done and still go on about its linear optical properties. In this thesis, some fundamental nonlinear optical phenomena including second harmonic generation (SHG), formation and recombination dynamics of excitons, and influence of ion implantation on SHG efficiency, as well as residual strain in ZnO epilayers grown on r-sapphire surfaces are investigated.
Ultrafast dynamics of formation and recombination of free excitons (FX) and neutral donor bound excitons (D0X) in high quality ZnO single crystals at different temperatures are investigated by utilizing time-resolved photoluminescence technique. Temporal behaviors of the first-order longitudinal optical (LO) phonon sidebands of FX and D0X in ZnO are also studied. In particular, time evolution of Fano resonance induced by the configuration interactions of exciton-phonon-impurity is observed.
Influence of ion-implantation on SHG efficiency in ZnO is studied by investigating the SHG signals of He-, Cu- and Zn-implanted ZnO single crystals and as-grown sample. The satellite peaks observed in the X-ray diffraction rocking curves of He- and Zn-implanted samples and prestigious simulations indicate the formation of quasi-interfaces in the ion-implanted region which results in some improvement of SHG efficiency in these samples.
Efficient SHG emission from thin ZnO crystal hollow rods/tubes is observed at room temperature. Multiple total reflections between the outer and inner surface of the tube structure are analyzed to be responsible for the observed enhancement of SHG efficiency.
Strains in a series of ZnO epilayers with the same film thickness grown on r-sapphire substrates by MOCVD at three different temperatures (450, 500, and 550oC) are investigated. Compressive strain is discovered in all the epilayers and found to decrease when the growth temperature goes up.