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 (SixPy) monolayers, which could be formed stably at the stoichiometries of y/x≥1. Interestingly, some of these compounds, i.e., P-6m2Si1P1 and PmSi1P2, have comparable or even lower formation enthalpies than their known allotropes. The band gaps (Eg) of SixPy compounds can be dramatically tuned in an extremely wide range (0<Eg<3 eV) by simply changing the number of layers. Moreover, we find that carrier doping can drive the ground state of C2/mSi1P3 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.