High quality epitaxial piezoelectric and ferroelectric wurtzite Al${}_{1-x}$Sc${}_x$N thin films

Piezoelectric and ferroelectric wurtzite are promising to reshape modern microelectronics because they can be easily integrated with mainstream semiconductor technology. Sc doped AlN (Al${}_{1-x}$Sc${}_x$N) has attracted much attention for its enhanced piezoelectric and emerging ferroelectric properties, yet the commonly used sputtering results in polycrystalline Al${}_{1-x}$Sc${}_x$N films with high leakage current. Here we report the pulsed laser deposition of single crystalline epitaxial Al${}_{1-x}$Sc${}_x$N thin films on sapphire and 4H-SiC substrates. Pure wurtzite phase is maintained up to $x=0.3$ with minimal oxygen contamination. Polarization is estimated to be 140 $\mu$C/cm${}^2$ via atomic scale microscopy imaging and found to be switchable via a scanning probe. The piezoelectric coefficient is found to be 5 times of undoped one when $x=0.3$, making it desirable for high frequency radiofrequency (RF) filters and three-dimensional nonvolatile memories.