Effect of post-annealing temperature and thickness on RF sputtered Al2O3 films for optoelectronic applications

In the present work, Al 2 O 3 films with varying thicknesses of 80,145 and 560nm have been fabricated using RF sputtering on Si (100) substrates. The films were then subsequently annealed at 600, 800 and 1000°C temperatures. The structural analysis via XRD revealed the polycrystalline ϒ-Al 2 O 3 phase with (440) plane as the preferred orientation for 145 and 560nm thickness annealed at 1000°C while all other films remain amorphous. The morphological analysis shows that the Al 2 O 3 films exhibit island growth patterns in the early deposition stages which transitioned to continuous and uniform films with an increase in thickness and annealing temperature. Interestingly, increased particle size and root mean square (RMS) roughness have been observed with the increase in annealing temperature. Furthermore, we noted the increase in diffuse reflectance with the increase in annealing temperature to 800°C while at 1000°C it slightly decreases. The optical energy gap of these films showed a reduction with the increase in annealing temperature. However, the refractive index and dielectric constant decrease with the increase in thickness. The observed structural and morphological modifications have been correlated with optical changes in Al 2 O 3 film due to thickness and annealing temperature. These results indicate that the optical properties of Al 2 O 3 films can be tailored by their structural and morphological characteristics, therefore offering valuable guidance for their application as an antireflection coating and surface passivation layer in optoelectronic devices. • Aluminium oxide films of different thicknesses were deposited by RF sputtering. • The deposited films were annealed at different temperatures. • Investigated the impact of thickness on the structure, morphology and optical properties of aluminum oxide films. • Investigated the impact of annealing temperature on the structure, morphology and optical properties of aluminum oxide films.