Phase stability of monolayer Si1−xGex alloys with a Dirac cone

Abstract

The phase stability and electronic properties of two-dimensional Si_1−xGe_x alloys are investigated via the first-principles method in combination with the cluster expansion and Monte Carlo simulations. The calculated composition–temperature phase diagram indicates that at low temperatures (below 200 K) monolayer Si_1−xGe_x alloys energetically favor phase separation, whereas when the temperature is increased above 550 K, Si_1−xGe_x alloys can be stabilized and thereby form solid solutions across the whole composition range. Special quasi-random structures were constructed to model the monolayer Si_1−xGe_x. The Si_1−xGe_x alloys are found to possess a robust Dirac cone against composition variation. These results provide a guideline for the experimental realization of Si_1−xGe_x alloys and monolayer Si_1−xGe_x alloys are believed to hold great potential for realization of applications in nanoelectronics and nano-optoelectronics.