Drastic evolution of point defects in vertically grown ZnO nanorods induced by lithium ion implantation

The evolution of various point defects in 100 keV lithium (Li) ion-implanted ZnO nanorods (NRs) by varying the fluences from 1 × 10¹⁴ to 7 × 10¹⁵ ions per cm² has been investigated experimentally and using a simulation by stopping and range of ions in matter (SRIM). The X-ray photoelectron spectroscopy results indicate that the Li¹⁺ ions have been incorporated at Zn²⁺ sites, which forms Li_Zn acceptors in the implanted NRs. The structural disorder and the number of oxygen vacancies in the implanted ZnO NRs increase drastically with an increase in the Li fluence as indicated by the X-ray diffractometry and Raman scattering analyses. Both the formation of acceptors and implantation-induced defects make the Li-implanted NRs electrically highly resistive. The yellow-orange photoluminescence (PL) emission of the as-grown ZnO NRs has evolved into green emission in the implanted NRs. A suppression of the green PL at higher fluences is possibly due to an apparent decrease in the zinc vacancy concentration. The SRIM results explain the quantitative energy loss, the distributions of the implanted Li ions and the point defects along the target ZnO NRs. The consistency between the experimental and theoretical simulations validates our analyses on the formation and evolution of various point defects in highly resistive Li-implanted ZnO NRs.