To learn more about the defect formation in the growth process, we have performed the EDX measurement for the samples grown under different percentages of In inclusion. Fig. 4 shows the variation of the composition of Zn and O contained in ZnO nanostructures with the percentage of In inclusion. Initially, the composition of zinc is less than that of oxygen. After indium inclusion, the zinc composition increases. The result is similar to the previous work for the inclusion of Se in the growth of GaN, in which the composition of gallium is reduced [14]. Since the composition of zinc is less than oxygen in the sample grown without In inclusion, the origin of defect emission may be attributed to Zn vacancies or O antisites. However, the energy level of Zn vacancy is too large (3.06 eV), so O antisite may be the most probable candidate. Many previous reports have also shown that O antisites may be responsible for the origin of defect emission in high oxygen content surroundings for ZnO materials [15]. With In inclusion, the composition ratio between oxygen and zinc decreases, and the number of O antisites will be reduced. The defect emission is therefore suppressed. This behavior may be understood as follows. Due to the weaker In–O bond than Zn–O bond, the migration velocity of indium is faster than zinc and oxygen atoms on the surface of ZnO crystal. Indium atoms can have more chance to reach Zn lattice site earlier than oxygen atoms during the growth, and O antisites would be reduced and the crystalline quality of zinc oxide would become more perfect. It thus leads to the changes in the morphology, crystallinity, defect density, as well as optical properties of the grown ZnO nanostructures.