The optical and electrical properties of gallium-doped ZnO thin film with post-annealing processes of various atmospheres

• Post-thermal annealing effects on grain sizes and activating Ga dopant of Ga–ZnO
• Post-annealing in acetylene ambient showed the best improvement on electricity.
• The electron mobility increases with annealing temperature due to larger grain size.
• Free carrier concentrations reach saturation while annealing temperature increase.

In this study, the GZO thin film were deposited with different RF powers and plasma gas of pure argon, 5% oxygen to argon ratio, and 10% oxygen argon ratio. After that, post-thermal annealing processes were performed at the temperature of 300 °C to 500 °C under vacuum, nitrogen, or acetylene ambient. The carrier concentrations and mobility exhibited different dependencies on these fabrication parameters, and that would reverse the conductivity order of as-sputtered samples. As a result, the carbon atom in the acetylene dissolved into the GZO thin film during post-thermal annealing and benefited the free carrier concentrations as another effective donor besides the gallium. The optical bandgap increased due to the increasing free carrier concentration, and made transparency still above 80%.

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