Phosphorus semiconductor overcomes resistance

Researchers believe a recently discovered blue form of ultrathin phosphorus - with tuneable electronic properties that enhance the injection of charge carriers into transistors - will help advance next-generation electronic devices.

Illustration of field effect transistors based on the recently discovered blue form of ultrathin phosphorous
Illustration of field effect transistors based on the recently discovered blue form of ultrathin phosphorous - © 2023 KAUST; Heno Hwang

Two-dimensional semiconductors, such as graphene and transition metal dichalcogenides, are expected to drive the miniaturization of electronic devices by providing ultrathin active channels for charge-carrier transport in field effect transistors (FETs).

FETs influence the flow of current through their channels by applied voltage and behave like electronically controlled switches or amplifiers. Electric resistance arises at the interfaces between the semiconductor channels and metal electrodes, limiting the charge injection into the devices and preventing FETs from reaching their full potential.

“Reducing this contact resistance will improve the current delivery capability and improve the performance of the FETs, which will pave the way for future microelectronics,” said Shubham Tyagi, a Ph.D. student in Udo Schwingenschlögl’s group at KAUST (King Abdullah University of Science and Technology) in Saudi Arabia.

Now, Schwingenschlögl’s team has designed a junction-free FET using two-dimensional blue phosphorene as the single electroactive material. Blue phosphorene is a semiconductor but becomes a metal when stacked into a bilayer.


“The ability of blue phosphorene to change its electronic properties based on stacking is crucial for our device,” Tyagi said in a statement. “Once we obtained a crystal orientation that delivers high carrier mobility through the channel, we were confident that we would achieve positive results because the contact resistance is addressed by the junction-free design.”

Central to the junction-free device is a blue phosphorene monolayer that, acting as the channel, lies between two metallic blue phosphorene bilayers that work as electrodes. The channel and electrodes consist of the same material, which results in a continuous structure, which reduces the resistance.

Using computer simulations, the researchers investigated the quantum transport in the proposed FET design for two different directions: armchair and zigzag. In both configurations, the FET effectively mediated electron transfer between channel and electrodes while meeting switching and amplification criteria. It outperformed devices using other two-dimensional materials, such as black phosphorene and monolayer molybdenum disulphide.

“In the future, we want to address different ways of improving the FET performance,” said Tyagi.

The researchers are working to reduce the current leakage between transistor gate and electrodes using van der Waals materials. They are also exploring ways to extend their ideas to magnetic materials to develop spintronic devices.

The team’s findings have been published in Nature.