Two-dimensional (2-D) layered materials have received considerable attention for their potential applications since the experimental discovery of graphene. Theoretical two-dimensional elementary semiconductors promise superior features in terms of fabrication, purification and doping. Few-layer black phosphorus (BP) is the first 2-D mono-elementary semiconductor with high electronic carrier mobility, strong optical absorption, linear dichroism, and high tunability with external fields. However, the flawed air stability and difficulties in large scale fabrication are remaining issues that inhibit practical applications of few-layer BP. Thus, researchers seek possible alternatives that also allow low-cost, large-scale synthesis, and offer good environmental stability without sacrificing the advantages of BP.