Theoretical evidence for enhanced piezoelectric properties of BY- or NaV-codoped wurtzite AlN

Enhancing the piezoelectric properties of wurtzite aluminum nitride (w-AlN) without compromising its structural stability presents a significant experimental and theoretical challenge. This study employs first-principles calculations to comprehensively investigate the structural stability and piezoelectric properties of BY- and NaV-codoped w-AlN. Analyses of formation enthalpy, phonon spectra, and AIMD molecular dynamics simulations demonstrate that the ordered alloy structure possesses better stability. The results confirm that the conventional ordered codoped configuration is energetically more favorable than its disordered counterpart. It was successfully predicted that the piezoelectric coefficients of (BY)_xAl_1-xN and (NaV)_xAl_1-xN alloys would be several times higher than that of pure wurtzite AlN. When the doping concentration reaches 50%, the piezoelectric strain constant d₃₃ of (NaV)_0.5Al_0.5N (22.37 pC N^-1) is 1.7 times that of (BY)_0.5Al_0.5N (13.26 pC N^-1), and reaches 5.4 times that of pure AlN (4.14 pC N^-1). The findings reveal that the enhanced polarization along the z-axis in (NaV)_xAl_1-xN results primarily from significant charge redistribution and lattice distortion induced by doping. In addition, another reason for the increase of piezoelectric strain constant d₃₃ is the weakening of the Al-N covalent bond sum. This work offers a theoretical foundation for enhancing the piezoelectric performance of w-AlN films, paving the way for their use in high-sensitivity sensing and acoustic device applications.