Abstract
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.
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