Effects of Sc-doping on the structure and physical properties of AlN: first-principles studies*

It was found in experiments that Sc doping can significantly improve the piezoelectric property of wurtzite AlN, making AlNSc compounds promising in the applications of piezoelectric acoustic device. However, the piezoelectric constant of Al$_{1-x}$NSc$_{x}$ drops quickly if the Sc doping content is larger than 43{\%}, probably due to the phase transition of Al$_{1-x}$NSc$_{x}$..$^{1,\, 2}$ In this work, we performed systematic first principles calculations on the strutural, mechanical and physical properties of Sc-doped AlN, as a dependence of Sc compositions, so as to understand how the Sc-doping affects the properties of AlN. The calculated lattice parameters and piezoelectric constant corresponds well with the experimental data, reaching to the peak at $x \quad =$ 43.5{\%}. Also we found that with the increasing Sc contents, the elastic constants of C$_{33}$, C$_{11}$ and C$_{44}$ decarese, whereas C$_{12}$ and C$_{13}$ increase. The total energy calculations show that Al$_{1-x}$NSc$_{x}$ with a wurtzite phase is more stable than the rocksalt phase as x \textless 31.25{\%}, and then the rocksalt Al$_{1-x}$NSc$_{x}$ that has few peizoelectric property is energetically preferred. Ab-initio molecular dynamic (AIMD) studies were further employed to analyze the phase transition of Al$_{0.5}$NSc$_{0.5}$. .1. A. Morito, K. Toshihiro, K. Kazuhiko, T. Akihiko, T. Yukihiro and K. Nobuaki, Advanced Materials \textbf{21}, 593-596 (2009). 2. O. Leon, A. Morán and R. Gonzalez, Applied Physics Letters \textbf{95}, 162107-162107-162103 (2009).