Prediction of a new phosphorus allotrope with tunable direct band gap and high mobility

Black phosphorus can be exfoliated to a few layers, belonging to the class of 2D materials. Thin black phosphorus has received much attention because of it high carrier mobility and moderate band gap which are promising for applications to nanoelectronic and nanophotonic devices. Besides black phosphorus, phosphorus can exist in many different forms in nature. Recently, blue phosphorus has been theoretically predicted and subsequently synthesized on gold substrate by experiments. The existence of a variety of phosphorus allotropes motivates our work to search for a new allotrope that provides more interesting characteristics than black phosphorus. Here, we report the prediction of a new P allotrope, called green phosphorus, using an evolutionary crystal structure search method. Green phosphorus has a layered structure with the interlayer interaction comparable to that of black phosphorus. Thus, it should be exfoliated to a few layers. As the film thickness decreases to a monolayer, green phosphorus exhibits strong anisotropy in the optical and transport properties. Due to the tunable direct band gap, green phosphorus is suitable for nanodevice applications. We discuss the effects of temperature and substrate on the possible synthesis of green phosphorus.