  Group IV and V monolayers are very crucial 2D materials for their high
carrier mobilities, tunable band gaps, and optical linear dichroism. Very
recently, a novel group IV-V binary compound, Sn2Bi, has been synthesized on
silicon substrate, and has shown very interesting electronic properties.
Further investigations have revealed that the monolayer would be stable in
freestanding form by hydrogenation. Inspired by this, by means of
first-principles calculations, we systematically predict and investigate eight
counterparts of Sn2Bi, namely Si2P, Si2As, Si2Sb, Si2Bi, Ge2P, Ge2As, Ge2Sb,
and Ge2Bi. The cohesive energies, phonon dispersions, and AIMD calculations
show that, similar to Sn2Bi, all of these freestanding monolayers are stable in
hydrogenated form. These hydrogenated monolayers are semiconductors with wide
band gaps, which are favorable for opto-electronic purposes. The Si2YH2 and
Ge2YH2 structures possess indirect and direct band gaps, respectively. They
represent very interesting optical characteristics, such as good absorption in
the visible region and linear dichroism, which are crucial for solar cell and
beam-splitting devices, respectively. Finally, the Si2SbH2 and Si2BiH2
monolayers have suitable band gaps and band edge positions for photocatalytic
water splitting. Summarily, our investigations offer very interesting and
promising properties for this family of binary compounds. We hope that our
predictions open ways to new experimental studies and fabrication of suitable
2D materials for next generation opto-electronic and photocatalytic devices.
