Effects of Al Diffusion Process on the Electrical, Optical, and Structural Properties of Transparent Conducting Al-doped ZnO

The effects of post-thermal diffusion of Al into heavily Al-doped ZnO (AZO) on its electrical, optical, and structural properties were investigated. Notably, the thermal diffusion of Al led to a significant enhancement of the optical transmittance-e.g., the transmittances at 550 nm were 90.4% and 96.7% before and after Al thermal diffusion, respectively. The structural analysis revealed that the improved optical transmittance was due to the combined effects of improved crystallinity, smoother surface, and the presence of transparent Al-O. However, the electrical properties of the AZO films after Al thermal diffusion were degraded-e.g., the sheet resistance was increased by 24% after thermal diffusion, which might be attributed to the generation of internal defects due to the heavy Al doping.