Highly ultraviolet-transparent ZnO:Al conducting layers by pulsed laser deposition

The Zn-rich ZnO:Al (AZO) thin films were grown on c-plane sapphire substrates by pulsed laser deposition using Ar atmosphere. The effects of substrate temperature on the characteristics of AZO films were investigated in terms of x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, optical transmittance and Hall measurements. From the temperature-dependent Hall measurements, all the as-deposited AZO films exhibit the metal-like conductivity behavior. It was found that the band gap of AZO films increased from 3.45 to 3.8 eV when the substrate temperature decreased from 700 to 100°C. The AZO film deposited at 100°C shows low resistivity of 233 μω cm and high transmittance in both visible and UV regions. The high transmittance of AZO films with large Zn content could be due to the formation of Zn nanoparticles, which is referred to surface plasmon resonance. Especially, the transmittance of AZO film (200 nm thick) can reach 91% at a wavelength of 365 nm, showing high potential in UV device applications.