Ellipsometric characterization of AlN films synthesized by Pulsed-Laser-Deposition

AlN films were synthesized on Si(100) by pulsed laser deposition at 800oC and different incident laser fluences in vacuum and in nitrogen at 0.1 Pa. Two KrF* (λ = 248 nm) excimer laser sources were used generating pulses of 7.4 and 25 ns duration, respectively. The incident laser intensity on target was kept constant in all experiments within (3-4)x108 W/cm2. The films were studied by ellipsometry (SE) in the spectral range λ = 190 to 900 nm and the optical parameters, such as refractive index, high frequency dielectric constant and single oscillator energies were estimated. The analysis of the SE results revealed that the films, deposited with short laser pulses and low laser fluence (3.7 J/cm2) were characterized with refractive index values higher than 2 and an optical band gap energy value of ∼ 5 eV, suggesting that their structure was polycrystalline with cubic crystallites. With longer laser pulses and large fluence the refractive index values decreased and the values of the energetic parameters increased suggesting that the films, deposited in vacuum were polycrystalline with hexagonal phase, while those, deposited in nitrogen at 0.1 Pa were amorphous.