Large piezoelectric and elastic properties in B and Sc codoped wurtzite AlN

Balancing the piezoelectric stress coefficient (e33) and the elastic constant (C33) of AlN-based materials is challenging but crucial for its application in bulk acoustic wave resonators. In this work, via first-principles calculations, we demonstrate that e33 and C33 can be simultaneously enhanced by adding boron (B) in the ScxAl1−xN system. Compared with ScxAl1−xN, the large C33 in B0.125Scx−0.125Al1−xN is caused by the shorter and stiffer B–N bonds, and the enhancement of e33 mainly comes from a larger sensitivity of atomic coordinates with respect to the strain (|du/dε|). Further investigation shows that the introduction of B in ScxAl1−xN significantly decreases the ratio of lattice parameter c over a due to the planar coordination preference of bulk BN, which is accompanied by an increased average |du/dε| and e33. Such a negative correlation can be attributed to the fact that |du/dε| of N is proportional to the asymmetry of transversal bond strengths but inversely proportional to the overall average bond strengths around N atoms. Such a bonding character observed in this work could be beneficial to the design of wurtzite materials with large piezoelectric coefficients and high elastic constants.