Highly stable two-dimensional silicon phosphides: Different stoichiometries and exotic electronic properties

The discovery of stable two-dimensional, earth-abundant, semiconducting materials is of great interest and may impact future electronic technologies. By combining global structural prediction and first-principles calculations, we have theoretically discovered several semiconducting silicon phosphide (Si_xP_y ) monolayers, which could be formed stably at the stoichiometries of y /x ≥1 . Interestingly, some of these compounds, i.e., P -6 m 2 Si₁P₁ and P m Si₁P₂ , have comparable or even lower formation enthalpies than their known allotropes. The band gaps (E_g) of Si_xP_y compounds can be dramatically tuned in an extremely wide range (0 <E_g<3 eV) by simply changing the number of layers. Moreover, we find that carrier doping can drive the ground state of C 2 /m Si₁P₃ from a nonmagnetic state into a robust half-metallic spin-polarized state, originating from its unique valence band structure, which can extend the use of Si-related compounds for spintronics.