Black phosphorus could pave the way for smaller and more energy efficient transistors, South Korean researchers have found.
In experiments with an only a few atoms thick layer of black phosphorus - a graphite resembling material created by heating the normal white phosphorus under pressure of more than 12,000 atmospheres - the team from South Korea’s Sungkyunkwan University found they could create adjustable high performance transistors.
By changing thickness of the black phosphorus layer, the researchers were able to switch the transistor between the high performance n-type, p-type and ambipolar mode (combining n and p properties).
This is a major advantage over conventional silicon-based transistors which need to be doped with another material to make it either of the two types needed for manufacturing of semiconductor chips.
While silicon-based chips are usually made into a sandwich-like structure with a layer of arsenic crystal between two silicon-boron crystals, black phosphorus transistors could have a form of a single lightweight black phosphorus layer. This way, black-phosphorus transistors could solve the problem the electronics industry is facing in its persistent race to create smaller and more powerful devices.
"The driving force in black phosphorus is the carrier mobility,” said David Perello, author of the experiment.” "Everything centres around that. The fact that the band gap changes with thickness also gives us flexibility in circuit design.”
High carrier mobility - the speed with which electrons can move through the material - gives black phosphorus the ability to operate at lower voltages while also increasing performance.
Even though conventional silicon-based technology may be reaching its limits, it still has multiple advantages over black phosphorus – first of all, the price. A scalable method for commercial manufacturing of black phosphorus has not yet been developed and the material is currently much more expensive than the omnipresent silicon.
"I don't think it can compete with silicon at the moment, that's a dream everybody has,” Perello said. “With the best silicon transistors we can achieve mobilities that are similar to what I was able to make in these BP devices. But the fact that it (the black phosphorus transistor) was so simple to make without having access to state of the art commercial growth, fabrication and lithography facilities means that we could make it significantly better."
The researchers believe the material could help solve one problem facing the nascent Internet of Things (IoT). Currently, a major constraint preventing IoT from taking off is the inability to scale down the component size and the lack of a long-term power solution. Two-dimensional layered materials, such as black phosphorus or graphene could offer a solution.