Laser annealing effects on Ga dopants for ZnO thin films for transparent conducting oxide applications

Ga-doped ZnO (GZO) thin films were prepared for transparent conducting oxide (TCO) applications. For the first time, Ga was successfully employed as an n-type dopant in ZnO materials. For the ionization process of the Ga dopant, an optical annealing process with a high energy was employed. The optimized contents of Ga dopants were tested and analyzed for the TCO applications. Additionally, different types of optical annealing processes were employed and tested for device applications. Before the optical annealing process, furnace annealing was performed as a basic process, and then rapid thermal annealing (RTA) or CO2 laser annealing processes were performed alternately or sequentially. In our experiment, we found that the sequence of the optical annealing process was important for the effectiveness of the annealing owing to the differences in the penetration depth of the wave and the applied energy density. We confirmed that a specific sequential combination of the RTA process and the CO2 laser annealing process can yield high-quality transparent conducing oxide thin films. GZO thin films post annealed using a sequential RTA and CO2 laser annealing methods exhibited the lowest conductance and transmittance values. Also, by introduction of Ga dopant, thin film can obtain high thermal and chemical stability due to its low reactivity and strong resistance to oxidation.