Density functional theory insights of phonons modes behaviours in AlScN for surface acoustic wave applications

Abstract

In this work, we investigate the phonons modes behaviors of scandium-doped aluminum nitride (Sc-AlN) using first-principles density functional theory (DFT). We analyze the phononic dispersion, phonon density of states, group velocity, and Raman spectra of ScAlN for various scandium concentrations and compare them with undoped AlN. Our results show that Sc doping is significantly affect the phononic properties of AlN, including the formation of defect states within the phononic band gap and changes in the group velocities of phonon modes. Our analysis reveals that the introduction of Sc dopants causes a notable narrowing of the phononic band gap in AlN. Additionally, we observe a zero group velocity in the band gap, indicating the suppression of phononic transmission through the material. Moreover, Sc doping also affects the Raman spectrum of AlN, by inducing new vibrational modes. The known E2(high) peak in the Raman spectrum of AlN shifts to lower frequencies upon Sc doping, and new peaks appear due to the interactions of scandium and the AlN lattice. Our findings highlight the importance of understanding the effects of dopants on the phononic properties of AlScN and have implications for the design and optimization of AlScN-based devices for acoustic wave applications