Excellent piezoelectric and ferroelectric properties of ScxGa1−xN alloy with high Sc concentration

Alloying wurtzite aluminum nitride and gallium nitride (GaN) with scandium (Sc) enhances the piezoelectric and ferroelectric properties, but increasing the Sc concentration while maintaining the wurtzite phase is a major challenge. We meticulously optimized the sputtering conditions to successfully obtain a high-Sc-concentration GaN alloy (ScxGa1−xN, 0.44 < x ≤ 0.53), which has not yet been achieved. The prepared ScxGa1−xN films exhibit excellent piezoelectricity and ferroelectricity. The maximum piezoelectric constant d33 of 33 pC/N exceeds the values of ScxAl1−xN used in radio frequency filters. The minimum coercive field of ferroelectricity Ec of 1.49 MV/cm is the lowest of any ferroelectric wurtzite to date and is comparable to those of state-of-the-art ferroelectric HfO2-based materials used in compute-in-memory for artificial intelligence. Structural analysis showed that the ScxGa1−xN films have a c-axis-oriented wurtzite texture without a rock salt phase. The lattice constant ratio c/a varies greatly depending on the sputtering conditions. Decreasing c/a causes d33 to increase almost linearly, and minimizing Ec requires a small c/a and high Sc concentration.