  Si-Ge monolayers (SiGeM) with different elementary proportion x (0<x<1) were
systematically studied for the first-time using ab initio calculations in this
work. The structural stabilities of the Si1-xGexM with different symmetries
were investigated using phonon spectra, and an infinite miscibility between Si
and Ge elements were revealed in the 2D honeycomb structures. The simulated
scanning tunneling microscope images and Raman and infrared active modes of the
Si1-xGexM were then obtained for structural characterizations. Interestingly,
the study of electronic properties revealed not previously reported oscillatory
nonlinear dependence of band gap values on the elementary proportion x in the
Si1-xGexM, which suggests an alternative way for tuning the band gaps of 2D
materials. Additionally, low effective masses (0.008m0 ~ 0.021m0) of the
carriers in the semiconducting Si1-xGexM were found, which has potentials for
high-speed applications. Considering the advantage of their compatibility with
current Si-based technology and the trend of miniature of electronic devices,
the Si1-xGexM with stable structures and excellent properties would be
important for 2D applications based on group IV materials.
