Huge Piezoelectric Response of LaN-based Superlattices

Abstract

We construct LaN-based artificial superlattices to investigate the ferroelectricity and piezoelectricity using the volume matching conditions of the parent components that soften the elastic constant <i>C</i>₃₃ and increase the piezoelectric modulus <i>d</i>₃₃. The proposed superlattice consists of LaN and YN (or LaN and ScN) buckled monolayers alternately arranged along the crystallographic <i>c</i>-direction. The structure of polar wurtzite (w-LaYN/w-LaScN) is both mechanically and dynamically stable, and the computed energy barrier makes the ferroelectric polarization switching possible. We show that the epitaxial strain can modify the spontaneous ferroelectric polarization as well as <i>d</i>₃₃. The LaN/YN superlattice exhibits a huge piezoelectric response in the unstrained state, due to their small <i>c</i>/<i>a</i> value and extremely soft <i>C</i>₃₃. In addition, the epitaxial strain is revealed as effective control of the nature (indirect and direct) and value of the electronic band gap.