Quasi-epitaxial growth of crystalline wurtzite AlN thin films on Si(001) by RF magnetron sputtering

Piezoelectric AlN films were grown on Si(001) substrates at 200°C by RF reactive magnetron sputtering technique. The optimization of the sputtering parameters (target-substrate distance, RF power, gas composition) resulted in the quasi-epitaxial growth of crystalline wurtzite AlN thin films. The structure and the morphology of the films were investigated by X-ray diffraction and atomic force microscopy techniques. These measurements showed that the AlN films were highly c-axis oriented, with low surface roughness. The structural and morphological characteristics of the best films were correlated to the gas composition of the optimized sputtering process. The piezoelectric constant d₃₃ of all the sputtered AlN films was measured and a value (15 pC/N) surprisingly much higher than that of the bulk single crystal was estimated for the highest quality AlN film.