  First-principles calculations are performed to study the structural stability
and spintronics properties of Janus MoGeSiP2As2 and WGeSiP2As2 monolayers. The
high cohesive energies and the stable phonon modes confirm that both these
structures are experimentally accessible. In contrast to pristine MoSi2P4, the
Janus monolayers demonstrate reduced direct bandgaps and large spin-split
states at K/-K. In addition, their spin textures exposed that breaking the
mirror symmetry brings Rashba-type spin splitting in the systems which can be
increased by using higher atomic spin-orbit coupling. The large valley spin
splitting together with the Rashba splitting in these Janus monolayer
structures can make a remarkable contribution to semiconductor valleytronics
and spintronics.
