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.