Low Temperature Growth of High-Quality Wurtzite Ferroelectric Through Quasi-van der Waals Epitaxy.

Wurtzite-type aluminum scandium nitride (AlScN) has emerged as a potential candidate for next-generation ferroelectrics due to large polarization, high Curie temperature and compatibility with semiconductor technology. However, strategies that enable the low-temperature growth of high-quality films, and the exfoliation of freestanding membranes are still lacking, largely hindering integration in functional devices. Here, we demonstrate the growth of high-quality AlScN films at the low temperature of 150°C on substrates with distinct crystal symmetries, achieved by using a two-dimensional transition metal dichalcogenide (TMDC) monolayer as a buffer. The high crystallinity is stemmed from the quasi-van der Waals epitaxy, which is universally demonstrated on a wide range of TMDC materials. The TMDC buffers further enable the fabrication of freestanding AlScN membranes, exhibiting excellent ferroelectric properties including high remanent polarization, low leakage current and rapid switching kinetics. Our findings provide a low-thermal-budget approach with high integration flexibility to develop wurtzite-based ferroelectric, piezoelectric, and electro-optic devices.