  Motivated by a recent experiment that reported the synthesis of a new 2D
material nitrogenated holey graphene (C$_2$N) [Mahmood \textit{et al., Nat.
Comm.}, 2015, \textbf{6}, 6486], electronic, magnetic, and mechanical
properties of nitrogenated (C$_2$N), phosphorated (C$_2$P) and arsenicated
(C$_2$As) monolayer holey graphene structures are investigated using
first-principles calculations. Our total energy calculations indicate that,
similar to the C$_2$N monolayer, the formation of the other two holey
structures are also energetically feasible. Calculated cohesive energies for
each monolayer show a decreasing trend going from C$_2$N to C$_2$As structure.
Remarkably, all the holey monolayers are direct band gap semiconductors.
Regarding the mechanical properties (in-plane stiffness and Poisson ratio), we
find that C$_2$N has the highest in-plane stiffness and the largest Poisson
ratio among the three monolayers. In addition, our calculations reveal that for
the C$_2$N, C$_2$P and C$_2$As monolayers, creation of N and P defects changes
the semiconducting behavior to a metallic ground state while the inclusion of
double H impurities in all holey structures results in magnetic ground states.
As an alternative to the experimentally synthesized C$_2$N, C$_2$P and C$_2$As
are mechanically stable and flexible semiconductors which are important for
potential applications in optoelectronics.
