Negative Poisson's ratio and anisotropic carrier mobility in ternary Janus Si2XY (X/Y= S, Se, Te): First-principles prediction

In this Letter, the structural, mechanical, electronic, and transport properties of two-dimensional (2D) ternary Janus Si2XY (X/Y= S, Se, Te) monolayers are studied based on the calculations using first-principles density functional theory. All three structures are found as direct semiconductors with moderated bandgap energies and good stabilities for experimental synthesis. The transport properties are also examined by calculating the carrier mobilities. We find that the carrier mobilities of all three monolayers are anisotropic not only between the electrons and holes but also between the two transport directions. The Si2SSe monolayer exhibited the highest electron mobility of 897.66 cm2 V−1 s−1 in the x axis. Amazingly, our calculations reveal that the Si2XY monolayers are auxetic materials with negative Poisson's ratio along both x and y axes. Particularly, the Si2SSe has the largest negative Poisson's ratio value of –0.131 in the x direction. These obtained results open more prospects for advanced applications of these materials in electronics, optoelectronics, and nanomechanics.