Blue second harmonic generation from aluminum nitride films deposited onto silicon by sputtering technique

We studied the second order optical nonlinearity of aluminum nitride films grown by sputtering onto silicon substrates. The crystalline properties of the films were investigated by x-ray diffraction measurements. Preliminary linear optical characterization of the films was carried out by spectrophotometric optical reflectance measurements at different incidence angles; thus the dispersion laws for both ordinary and extraordinary refractive indices were retrieved. Finally, second harmonic generation measurements in reflection mode were performed at a fixed angle from a fundamental beam provided by a picosecond Ti:sapphire laser system at lambda=800 nm. In the experiments a high blue light conversion efficiency was found for samples 1.5 and 2 mu m thick, and the second order nonlinear coefficient d(33)=11 +/- 1 pm/V was found.