Strain-induced phase transitions and high carrier mobility in two-dimensional Janus MGeSN 2 (M = Ti, Zr, and Hf) structures: first-principles calculations.

In this study, we construct new 2D Janus MGeSN 2 (M = Ti, Zr, and Hf) monolayers and systematically investigate their electronic band structures under applied biaxial strain. Their crystal lattice and electronic as well as transport properties are also examined based on the first-principles calculations and deformation potential theory. The results show that the MGeSN 2 structures have good dynamical and thermal stability, and their elastic constants satisfy the criteria of Born-Huang also indicating the good mechanical stability of these materials for experimental synthesis. Our calculated results indicate that the TiGeSN 2 monolayer exhibits indirect-bandgap semiconductor characteristics whereas the ZrGeSN 2 and HfGeSN 2 monolayers exhibit direct-bandgap semiconductor characteristics. Importantly, the biaxial strain shows significant influences on the electronic energy band structures of the monolayers in the presence of a phase transition from semiconductor to metal, which is an important feature of these materials for their application in electronic devices. All three structures exhibit anisotropic carrier mobility in both x and y transport directions, suggesting their great potential for application in electronic devices.