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 $({\mathrm{Si}}_x{\mathrm{P}}_y)$ monolayers, which could be formed stably at the stoichiometries of $y/x\ge 1$. Interestingly, some of these compounds, i.e., $P\text{−}6m2{\mathrm{Si}}_1{\mathrm{P}}_1$ and $Pm{\mathrm{Si}}_1{\mathrm{P}}_2$, have comparable or even lower formation enthalpies than their known allotropes. The band gaps $\left(E_g\right)$ of ${\mathrm{Si}}_x{\mathrm{P}}_y$ 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 $C2/m{\mathrm{Si}}_1{\mathrm{P}}_3$ 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.

• Received 3 November 2014
• Revised 13 February 2015

DOI:https://doi.org/10.1103/PhysRevB.91.121401