Piezoelectric response enhancement of w-AlN by Hf (or Zr) and Sc co-alloying: A first principles study

In this report, rigorous calculations based on density functional theory have been performed to study the piezoelectric and elastic properties of wurtzite aluminum nitride (w-AlN) with single- and co-alloying by Hf (or Zr) and Sc. It is found that the (HfSc)0.375Al0.625N and (ZrSc)0.375Al0.625N with stable wurtzite phase, exhibit a piezoelectric coefficient d33 as large as 49.18 pC/N and 47.00 pC/N, respectively. However, the piezoelectric voltage constant g33 and electromechanical coupling constant k2 33 of HfAlN, ZrAlN, HfScAlN, and ZrScAlN are smaller than that of the ScAlN counterpart, which is due to the large dielectric constant ε33 of Hf (or Zr) alloying samples. Furthermore, the internal parameter u and the bond angle α were calculated to elucidate the brittle-to-ductile transformation in alloying w-AlN crystal structure. Electronic structure calculations show that the bandgap decreases almost linearly concerning the increase of alloying concentration, and the Hf (or Zr) alloying compounds become n-type semiconductors due to the existing high-charge states.