“…Their monolayer structures are closely related to that of arsenic, which can be viewed as replacement of every fourth atom in the arsenic layer by a (Ge, or Sn, In) atom and of the rest by phosphorus (P) atom. Examples in this class of 2D materials include combination of phosphorus with group-II, III, and IV elements, which result in easily exfoliable 2D materials with low cleavage energies for monolayer, such as calcium triphosphide (CaP 3 ), 20 indium triphosphide (InP 3 ), 21 tin triphosphide (SnP 3 ), 22 and germanium triphosphide (GeP 3 ). 23 In particular, monolayer GeP 3 23 was theoretically predicted to be a novel 2D structure with tunable indirect bandgaps, high carrier mobilities, and an excellent absorption coefficient in the range of solar spectrum, and it can be easily exfoliated from GeP 3 bulk material.…”