Enhancing the piezoelectric modulus of wurtzite AlN by ion beam strain engineering

The piezoelectric modulus of wurtzite aluminum nitride (AlN) is a critical material parameter for electrical components, ultimately contributing to the energy efficiency and achievable bandwidth of modern communication devices. Here, we demonstrate that the introduction of metallic point-defects (Ti, Zr, Hf) improves the piezoelectric modulus of as-received, unstrained, epitaxially grown AlN. The metals are incorporated by ion implantation with an acceleration energy of 30 keV to a fluence of 1015 at cm-2, which causes an elongation along the wurtzite c-axis. The stored internal strain energy increases the piezoelectric polarization of the thin AlN layer. This can equivalently be described by an enhancement of the piezoelectric modulus d33. The incorporation of 0.1 at. % Ti enhances the piezoelectric modulus by ∼30%; significantly exceeding gains obtained by alloying with the same amount of Sc.