Influence of Nitrogen Carrier Gas on the Optical, Structural, Mechanical and Electrical Properties of Aluminium-Doped Zinc Oxide Thin Films Deposited via AACVD

Abstract

This study analyses the optical characteristics, together with the structural, mechanical, and electrical attributes of Aluminium-doped Zinc Oxide (AZO) thin films produced through Aerosol-Assisted Chemical Vapour Deposition (AACVD), using nitrogen (N₂) gas as the transport medium. The deposition occurred at 400°C, while the soda-lime glass substrates received annealing treatment at 450°C within a nitrogen atmosphere.  X-ray Diffraction (XRD) analysis showed improved crystal formation through distinct peaks at (220), (311), and (222), as aluminium-doping levels rose and simultaneously generated small crystallite particles, rising dislocation density levels with expanded lattice deformations. The Scanning Electron Microscopy analysis revealed hexagonal ZnO grains evolved into irregularly shaped small grains, accompanied by higher densities of defects as Al compositions increased in the ZnO material. Profilometry analysis showed that the ZnO  film layer got thicker from 102 nm in undoped ZnO to 115 nm in 20% Al-doped ZnO. The maximum UV absorbance took place at 5% Al doping, while the bandgap expanded from 3.21 eV (undoped ZnO) to 3.33 eV (20% Al-doped ZnO) from the UV-Visible spectroscopic analysis, which is attributed to the Burstein-Moss effect. The peak concentration of 1.0 × 10²¹ cm⁻³ carriers was observed during Hall effect tests at 5% Al doping, yet it decreased as the doping concentration surpassed this level, due to defects that  trapped additional charges. More than half of the doping groups (Al) improved UV ray absorption between 15-20%, but the film’s mechanical structure deteriorated during testing. The study demonstrates the efficiency of nitrogen gas in modifying AZO film characteristics, which results in suitable applications for transparent electrodes, solar cells, and photodetectors, because of its adaptable electrical and optical features.