Tuning structural and electronic properties of two dimensional Si and Ge based random alloys: an ab initio study

By plane-wave pseudopotential techniques we simulated structural and electronic properties of novel two-dimensional (2D) materials composed of Si and Ge randomly placed at the lattice sites of a honeycomb structure: 2D-Si1−xGex, and 2D-(H@Si)1−x(Ge@H)x, the corresponding H-passivated alloy. We investigated the formation of a random network of Si and Ge in 2D-honeycomb structure and proved the thermal stability of H-passivated SiGe alloy by computing the formation energy of these 2D-compounds. The 2D-Si1−xGex random alloy is a semi-metal and presents at the Fermi energy a density of states resembling the one produced by the Dirac’s cone of silicene and germanene, suggesting the possibility to induce, in 2D-Si1−xGex Dirac’s cone, a population of high velocity carriers that behaves like massless Dirac fermions. The 2D-(H@Si)1−x(Ge@H)x random alloy is a semiconductor and presents a tunable direct bandgap that doubles by decreasing the concentration from x = 1 to x = 0.25, making this 2D-alloy suitable for opto-electronic applications. The lattice parameter of both 2D-alloys increases linearly with Ge concentration, thus providing a microscopic mechanism to engineer the lattice parameter and/or the electronic properties of 2D-heterostructures based on these 2D-materials. The study of elastic properties of 2D-@Si1−xGex and 2D-(H@Si)1−x(Ge@H)x as a function of x for possible use in flexible electronics and the investigation of magnetic properties of partially H-passivated 2D-(H@Si)1−xGex random alloy for concentration close to x = 0.5 for spintronic applications complete the work. Graphical abstract