Effects of Deposition Parameters on the Optical and Piezoelectric Properties of Aluminum Scandium Nitride

Alloying aluminum nitride with scandium nitride could result in an increase of the piezoelectric coefficient, leading to impacts on next-generation RF-filters. Aluminum scandium nitride (Al_1-xSc_xN) also has uses in opto-electronic applications. To incorporate Al_1-xSc_xN in devices, a better understanding of growth, structural, optical, and piezoelectric properties is needed. In this work we report the impacts of various growth parameters on microstructure and surface morphology of Al_1-xSc_xN films on (0001)-orientated sapphire substrates. Growth parameters were correlated with changes in optical and piezoelectric properties. Films were deposited from an Al_0.9Sc_0.1 target by reactive controllably unbalanced magnetron sputtering. X-ray diffraction was used to characterize crystallinity of the films. Comparing full-width half-maximum, peak intensity, and 2Θ position of diffraction peaks shows that crystallinity is affected by f_N2, j_i/j_Me, T_sub, and W_T. Atomic force microscopy (AFM) was used to determine surface morphology and piezoelectric coefficient of the films. AFM showed that at lower T_sub and W_T the films had large clusters on the surface and high surface roughness. The optical properties were determined by spectroscopic ellipsometry.