Nonmonotonic Enhancement of Electro‐Optic Properties of Wurtzite AlN Thin Films by Sc Doping

Wurtzite ferroelectrics, such as Sc‐doped AlN, have recently attracted considerable attention for their potential in realizing compact and scalable photonic integrated circuits due to the remarkable remanent polarization and compatibility with mainstream semiconductor processes. To unveil the electro‐optic (EO) response, epitaxial Sc‐doped AlN thin films were grown on yttria‐stabilized zirconia (111) substrates covered with indium tin oxide by radio‐frequency magnetron sputtering. All thin films exhibit an evident linear EO response, and the estimated EO coefficient, r c , initially falls and then rises as the Sc content increases, a trend of which agreed with the theoretical prediction. When the Sc content exceeds 21%, a sign reversal of the phase occurs, which is attributed to the change in polarity of the Sc‐doped AlN thin films. These results suggest that further increases in Sc content may yield EO response comparable to or even superior to that of LiNbO 3 , a present representative EO material, expanding the potential photonic applications of Sc‐doped AlN thin films.