Move Over Graphene, a New Transistor Material Is in Town!

by | Feb 7, 2017 | Technology Featured

Graphene, long hailed as one of engineering’s greatest wonder materials, may have found a competitor in phosphorene. Though graphene—made of single layers of carbon atoms—exhibits incredible flexibility and strength along with unique electrical properties, it has one fatal flaw: it’s not a natural semiconductor. This makes it very hard to use in transistors. However, phosphorene, which has a very similar structure in that it is made up of single layers of black phosphorus, has very promising superconductive properties.

The Discovery of Phosphorene

Black phosphorus was discovered about a century ago. It forms when phosphorus is subjected to high pressure, and possesses superconductive properties. In 2014 at Purdue University, a team of researchers was able to isolate a single layer of black phosphorus to create phosphorene. Since that time, phosphorene has been widely investigated by other researchers in the field. In one year alone, over four hundred papers about phosphorene were published. As more and more research comes to light, excitement over phosphorene’s potential to supplant less efficient materials in the field of electronics.

The Future of Transistors

Two-dimensional materials, like graphene or phosphorene, have long been expected to succeed silicon as the transistor material of the future. The International Technology Roadmap for Semiconductors (ITRS) predicts that this will happen around 2028. Graphene has been the traditional favorite for this slot, but alternative miracle materials like silicene and molybdenum disulphide—and now phosphorene—have also been investigated by scientists as well.

Though it is often hailed as the natural successor of silicon, graphene has a few very serious problems. Not only does it lack bandgap, it is not compatible with silicon. A material that is compatible with silicon would be able to hasten silicon photonics, which means that in future chips, light rather than electricity could be used to carry electrical signals. Any new transistor material (be it graphene or phosphorene) will have very different electromagnetic emission and interference properties from silicon, requiring a learning curve from electrical engineers responsible for EMI compliance testing.

The Advantages of Phosphorene

Phosphorene solves many of the problems that graphene has. It is a very potent semiconductor, meaning that its conductivity can be switched off and on. This allows engineers to modify how much energy is flowing through phosphorene at any given moment. This level of control keeps the amount of current that escapes to a minimum, bringing transistors one step closer to perfect efficiency. Conventional silicon transistors are hugely inefficient in comparison.

Phosphorene photodetectors have been found to be able to transfer signals to silicon photonic circuits at a level on par with germanium, which is commonly considered to be the ultimate photodetector. Though phosphorus is highly reactive in nature, but black phosphorus is extremely stable. Its crystalline form can be bonded to a silicon substrate. Using such a setup with 20 single-atom layers of phosphorene, researchers at the University of Minnesota were able to transmit signals along optical circuits at three gigabits per second.

Perhaps phosphorene’s greatest advantage is the fact that it has a bandgap, while graphene doesn’t. The presence of a bandgap means that phosphorene can be used to detect light. This bandgap can also be modified by controlling the number of phosphorene layers that are stacked atop silicon. By doing this, it is possible for light in both the infrared and visible ranges to be absorbed and used for communications.

The Applications of Phosphorene

Because of its unique properties, phosphorene has a lot of potential in the field of materials science. Though some of its qualities make it ideal for use in transistors, it may also have other uses. Phosphorene is not nearly as brittle as silicon, making it ideal for use in flexible electronics. Its light-emitting qualities also make it a contender for use in LEDs or lasers… or perhaps its most promising applications lie somewhere that hasn’t been discovered yet! Interest in such two-dimensional materials is increasing all over the world. These materials—such as silicene, germanene, stanine, and even graphene—along with their unique properties will surely change the world in ways we haven’t even begun to imagine.

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