Reversal barrier and ferroelectric polarization of strained wurtzite Al1−xScxN ferroelectric alloys

Reducing the reversal barrier of Al1−xScxN ferroelectric alloy is critical for improving the coercive voltage and power consumption of ferroelectric devices. Here, the synergistic effect of alloy composition and strain is introduced to optimize the ferroelectric properties of Al1−xScxN alloys. Because of the increased Al–N ionic bond character and the contribution of Sc-d orbitals, the spontaneous polarization, reversal barrier, and bandgap all reduce as the Sc concentration increases. Strain engineering improves the electron's electric dipole moment, resulting in a significant increase in spontaneous polarization (145.93 μC/cm2 for Al0.625Sc0.375N alloy). Meanwhile, the horizontal tension and vertical compression lower the reversal barrier of Al0.625Sc0.375N alloy to 95.45 meV/f.u., significantly lower than that of orthorhombic HfO2. Interestingly, the bandgap of Al1−xScxN alloy with low Sc concentration rises initially and then decreases as horizontal strain varies from compression to tension, whereas that of Al1−xScxN alloy with high Sc concentration monotonically decreases. The Al1−xScxN alloy exhibits the opposite tendency under vertical strain. These findings provide a thorough understanding of Al1−xScxN ferroelectric alloys and a guideline for designing high-performance Al1−xScxN ferroelectric alloys.