Experimental Study of Aluminum-Doped Nickel Oxide Thin Films Fabricated Using Pulsed Laser Deposition

Abstract

Thin films of pure nickel oxide (NiO) and Aluminum-doped nickel oxide (NiO-Al, 2%) were prepared and studied using pulsed laser deposition on glass substrates. X-ray diffraction (XRD) analysis revealed that Aluminum doping induces a slight increase in the average crystallite size from approximately 37 nm for the pure samples to about 42.6 nm for the doped films, while maintaining high homogeneity and a smooth surface with vertical roughness not exceeding 31 nm. Field-emission scanning electron microscopy (FE-SEM) results showed that the average grain size of the pure NiO film was 37.82 nm, whereas the doped NiO-Al (2%) film exhibited a larger grain size of 47.65 nm.

Optical characterization indicated an enhancement in absorbance, with absorption coefficients for both pure and doped films reaching values of α ≥ 10⁴ cm ^-1. This confirmed that the electronic transitions in the films were of the allowed direct type. The optical band gap of the pure NiO film was determined to be 3.92 eV, while that of the doped NiO-Al (2%) film decreased to 3.60 eV. The film thickness was measured to be 158 nm. This reduction in band gap is attributed to the introduction of intermediate energy levels within the band gap by Aluminum dopants.

These findings demonstrate that NiO-Al (2%) thin films combine a homogeneous nanostructure, high-quality smooth surfaces, and enhanced, tunable optical response. Consequently, they are promising candidates for advanced applications such as photodetectors, gas sensors, solar cells, and optoelectronic devices with adjustable performance.