Two-dimensional Si–Ge monolayers: Stabilities, structures, and electronic properties

Abstract

Si–Ge monolayers (SiGeMLs) with different elementary proportions x (0 < x < 1) were systematically studied for the first time using ab initio calculations in this work. The structural stabilities of the Si1 − xGexML with different symmetries were investigated using phonon spectra, and an infinite miscibility between Si and Ge elements was revealed in 2D honeycomb structures. The simulated scanning tunneling microscope images and Raman and infrared active modes of the Si1 − xGexML were then obtained for structural characterizations. Interestingly, the study of electronic properties revealed previously unreported oscillatory nonlinear dependence of bandgap values on the elementary proportion x in the Si1 − xGexML, which suggests an alternative way for tuning the bandgaps of 2D materials. Additionally, low effective masses (0.008 m0–0.021 m0) of the carriers in the semiconducting Si1 − xGexML were found, which have the potential for high-speed applications. Considering the advantage of their compatibility with current Si-based technology and the trend of miniature electronic devices, the Si1 − xGexML with stable structures and excellent properties would be important for 2D applications based on group IV materials.