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.
- The crystalline symmetries of layered black phosphorus and its isoelectronic group IV monochalcogenides play a very important role in the determination of their physical properties.
- Black phosphorus is likely to be the layered semiconductor material with the highest carrier mobility at room temperature, making it promising for high-performance electronic applications.
- Black phosphorus, arsenic phosphorus and other group V alloys may find applications in mid-infrared photonics as alternative material systems owing to their layered nature and moderate bandgap.
- Monolayer group IV monochalcogenides have a broken inversion symmetry and spontaneous in-plane electric polarization. They present a great platform for the exploration of piezoelectricity, ferroelectricity, ferroelasticity and multiferroics.
- In black phosphorus and other group V alloys, the interplay between the crystal symmetry and spin–orbit coupling may lead to the realization of rich topological states.
- Wafer-scale synthesis of this group of materials remains challenging. Future research may leverage the phase transition induced by pressure, temperature or high-intensity light.