Crystallization and optoelectronic properties of indium-Zinc-Oxide thin films annealed in argon and vacuum

Multi-component oxides based on the In₂O₃ – ZnO system has recently gained much attention as an alternative transparent conducting oxide. In₂O₃ and ZnO react to form several homologous compounds of the form Zn_kIn₂O_k+3, some of which possess excellent electrical and optical properties. Although the appearance of an amorphous-like phase has been reported at intermediate Zn/(In + Zn) ratios, little work has been done on the effect of post-deposition heat treatment on such IZO films. In this work, representative samples of IZO deposited in different ambience and conditions by radio-frequency magnetron sputtering exhibiting an amorphous diffraction pattern were annealed in an argon atmosphere of 1.6 × 10² mbar and vacuum of 10^-6 mbar at 500°C for 1 hour. XRD and SEM studies of the annealed films showed a marked difference in both the diffraction pattern and surface morphology after annealing. A variety of morphology, including dendrite-like patterns radiating outward was observed. The electrical and optical properties of the IZO films after annealing were also studied. Results show that while crystallinity of the films was improved after annealing, the electrical conductivity was reduced by several orders of magnitude. Annealing also seems to induce the crystallization of multiple phases in IZO films.