Black phosphorus and its isoelectronic materials

The family of 2D and layered materials has been expanding rapidly for more than a decade. Within this large family of hundreds of materials, black phosphorus and its isoelectronic group IV monochalcogenides have a unique place. These puckered materials have distinctive crystalline symmetries and exhibit various exciting properties, such as high carrier mobility, strong infrared responsivity, widely tunable bandgap, in-plane anisotropy and spontaneous electric polarization. Here, we review their basic properties, highlight new electronic and photonic device concepts and novel physical phenomena and discuss future directions.