Optical and structural properties of ion-implanted InGaZnO thin films studied with spectroscopic ellipsometry and transmission electron microscopy

Amorphous InGaZnO (IGZO) thin films were grown using RF sputtering deposition at room temperature and their corresponding dielectric functions were measured. In order to reduce defects and increase carrier concentrations, we examined the effect of forming gas annealing and ion implantation. The band gap energy increased with increasing forming gas annealing temperature. We implanted the IGZO thin films with F^- ions in order to decrease oxygen vacancies. For comparison, we also implanted InO^- ions. Transmission electron microscopy showed that the amorphous phase undergoes transformation to a nanocrystalline phase due to annealing. We also observed InGaZnO₄ nanocrystals having an In-(Ga/Zn) superlattice structure. As the annealing temperature increased, the optical gap energy increased due to crystallization. After annealing, we observed an oxygen-vacancy-related 1.9eV peak for both unimplanted and InO-implanted samples. However, F^- ion implantation substantially reduced the amplitude of the 1.9eV peak, which disappeared completely at a F fluence of 5 × 10¹⁵cm^-2. We observed other defect-related peaks at 3.6 and 4.2eV after annealing, which also disappeared after F implantation.