Second harmonic generation (SHG) and X-ray diffraction rocking curves of high-quality ZnO single crystals implanted by different ions (He, Cu, and Zn) were investigated. Interestingly, it was found that both He- and Zn-implanted samples show a convinced increment in SHG efficiency while the Cu-implanted one does not. X-ray diffraction rocking curves of the samples show satellite structures, and the simulations firmly reveal the formation of quasi-interfaces inside He- and Zn-implanted crystals. These quasi-interfaces lead to SHG improvement in the two samples. Polarization dependence of SHG of the samples on the excitation light also evidences this conclusion.

Effects of MgO deposition on Si∕SiO2 system and charge carrier trapping and recombination in Si∕SiO2∕MgO structures are studied using second-harmonic generation (SHG). An ultrafast 800nm laser was used both for multi-photon induced electron injection through the SiO2 into a potential well in the MgO, and for monitoring the time-dependent SHG signal, which is sensitive to the electric field at the Si∕SiO2 interface. Our results indicate that the MgO deposition introduces new trap states, and electrons trapped in the MgO transport more readily through the SiO2 than those in traps on the surface of SiO2. We attribute this to differences in trap energy levels and/or differences in process damage-induced defect densities in the SiO2.

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