In a recent discovery, researchers have found that, Black Phosphorus could possibly replace silicon as the primary material for electronics. The research team from Yale University, led by Fengnian Xia, Yale's Barton L. Weller Associate Professor in Engineering and Science, states how the long forgotten element could play a crucial role in the future of electronic and optoelectronic devices.
With silicon as a semiconductor, the quest for ever-smaller electronic devices could soon reach its limit. However, black phosphorus, with a thickness of just a few atomic layers, could usher in a new generation of smaller devices, flexible electronics, and faster transistors. According to the researchers, it’s basically due to two key properties; one, that the black phosphorus has a higher mobility than silicon - that is, the speed at which it can carry an electrical charge. The other is that it has a band-gap, which gives a material the ability to act as a switch; i.e. it can turn on and off in the presence of an electric field and act as a semiconductor. Graphene, another material that has generated great interest in recent years also has a very high mobility, but no band-gap.
However, finding a way to control the band-gap of black phosphorus is critical to realizing its potential applications. To that end, the researchers have discovered that the material's band-gap is most controllable at a certain thickness. By applying a vertical electric field to the material at that thickness, the researchers can "tune" the band-gap, essentially shrinking the moderate gap to the point where it nearly closes. That opens up many potential applications for black phosphorus, such as imaging tools, night vision devices, mid-infrared optical modulators, on-chip spectroscopy tools, and other optoelectronic technologies.
Finding the optimum thickness took some trial and error according to the team. At first, they tried a 4-nanometer thick sample, and found that the band-gap tuning was not very pronounced. They also noted that having a band-gap that can be controlled, means that black phosphorus could potentially be used as a topological insulator, a material with the unusual ability to serve as both an insulator (inside the material) and as a conductor (on its surface). Researchers are particularly interested in topological insulators, since they could be the key to developing low-power electronics in which electrons at the surface do not suffer from scattering.