Pulsed laser deposited alumina thin films

Thin films of amorphous alumina were fabricated using pulsed laser deposition. Topography, structural, and optical properties of alumina films were investigated depending on process parameters, specifically deposition time under vacuum and partial pressure of argon. Deposited films present good uniformity with RMS roughness ranging from 0.35 to 2.50 nm. Alumina films with thickness lower than 40 nm deposited under vacuum present a non-negligible void content that induces a decrease of the effective refractive index of the layers. Furthermore, introduction of argon gas (at 5×10−4 and 5×10−2 mbar) during the deposition process induces grainy structure of the thin films documented by an increase of RMS roughness from 0.35 to 1.5 nm. A decrease of the alumina layers' refractive index is observed in the 300-7500 nm spectral range when increasing Ar pressure.