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-6m2Si(1)P(1) and PmSi1P2, have comparable or even lower formation enthalpies than their known allotropes. The band gaps (E-g) of SixPy 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 C2/mSi(1)P(3) 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.