Structural and optical characterization of sol-gel processed Al-doped ZnO waveguide films for integrated optical devices

In this work, pure and Al-doped zinc oxide (AZO) thin films were grown on glass substrates by sol-gel spin coating method. Structural, morphological, optical and waveguiding properties are investigated for different Al concentration (0-4 at. %). X-ray diffraction confirmed the hexagonal ZnO Wurtzite structure of the films with a high c-axis preferred orientation. The crystallite size decreased from 30 to 20 nm with increasing Al content. Atomic force microscopy showed that Al-doped ZnO films presented a smooth and uniform surface and their roughness values depend on dopant concentration.The AZO films showed a high optical transparency more than 95% in the visible region and the optical band gap increased by increasing Al content. The optical waveguiding characterization demonstrated that our films have planar waveguide structure. All the AZO films supported only a well-guided fundamental mode for both transverse electric and transverse magnetic polarizations. Both ordinary and extraordinary refractive indices are found to decrease with Al doping content. Best performing thin films have been obtained with 2 at. % of Al.

Automated summary

Al-doped zinc oxide (AZO) thin films were found to have smooth and uniform surfaces, with decreasing grain size as Al content increased. They exhibited high optical transparency in the visible region, and the optical band gap increased with Al content. The best performing films were obtained with 2 at. % of Al doping.