Theoretical investigation of the piezoelectric and surface acoustic wave properties of GeSn alloys

Abstract

The piezoelectric and dielectric constants of Ge1-xSnx with varying concentrations (x∈(0–1.0) were calculated using the first-principles method based on the density functional theory, and the surface acoustic wave (SAW) properties such as phase velocity, electromechanical coupling coefficient k2, and power flow angle (PFA) were obtained for Ge0.5Sn0.5 from using the Christopher equations in different orientations (0–90°, 0–90°, and 0–180°). The results demonstrate that the piezoelectric and dielectric constants of Ge1-xSnx deviate from Vegard's law when the x is varied, and the piezoelectric constant value reaches a maximum when x = 0.5. Additionally, the SAW velocity of Ge1-xSnx can be tuned by changing the Sn concentration. It can be seen from the contour maps of Ge0.5Sn0.5 at orientations (45°, 0–90°, and 0–180°), many orientations exhibit outstanding SAW performance. Orientations with large k2 and zero PFA are selected as promising candidates for fabricating SAW devices, which has important significance for experimental research.