Effect of annealing atmosphere (Ar vs. air) and temperature on the electrical and optical properties of spin-coated colloidal indium tin oxide films

摘要

Colloidal indium tin oxide (ITO) ~6 nm nanoparticles synthesized in-house were deposited by spin coating on fused silica substrates, resulting in high resistivity films due to the presence of passivating organics. These films were annealed at various temperatures ranging from 150 to 750 C in air and argon atmospheres. The films are very transparent in the as-coated form, and they retain high transparency upon annealing, except the films annealed at 300 C in argon, which became brown due to incomplete pyrolysis of the organics. Thermogravimetric analysis and Raman characterization showed that the removal of organics increases with an increase in the annealing temperature, and that this removal is more efficient in the oxidizing atmosphere of air, especially in the 300-450 C temperature range than in Ar. Although ITO defect chemistry suggests that argon annealing should result in higher carrier concentration than air annealing, the faster removal of insulating organics upon annealing in air resulted in significantly lower film resistivity at intermediate annealing temperatures for films annealed in air than in Ar. At higher annealing temperatures, both Ar and air annealing, resulted in comparable film resistivities (the lowest achieved was ~10~0 Ω cm).