30 March 2017

NCSU converting p-type reduced graphene oxide to n-type

With support from the US National Science Foundation (NSF), North Carolina State University (NCSU) has developed a technique for converting positively charged (p-type) reduced graphene oxide (rGO) into negatively charged (n-type) rGO, creating a layered material that can be used to develop rGO-based transistors for use in electronic devices (Anagh Bhaumik and Jagdish Narayan, ‘Conversion of p to n-type Reduced Graphene Oxide by Laser Annealing at Room Temperature and Pressure’, Journal of Applied Physics; DOI: 10.1063/1.4979211).

“Graphene is extremely conductive, but is not a semiconductor; graphene oxide has a bandgap like a semiconductor, but does not conduct well at all – so we created rGO,” says Jay Narayan, the John C. Fan Distinguished Chair Professor of Materials Science and Engineering at NC State. “But rGO is p-type, and we needed to find a way to make n-type rGO,” he adds. “Now we have it for next-generation, two-dimensional electronic devices.”

Specifically, Narayan and Bhaumik – a Ph.D. student in his lab – demonstrated two things. First, they were able to integrate rGO onto sapphire and silicon wafers – across the entire wafer.

Second, they used high-powered laser pulses to disrupt chemical groups at regular intervals across the wafer. This disruption moved electrons from one group to another, effectively converting p-type rGO to n-type rGO. The entire pulsed laser deposition (PLD) process is done at room temperature and pressure using high-power nanosecond laser pulses, and is completed in less than a fifth of a microsecond. The laser radiation annealing provides a high degree of spatial and depth control for creating the n-type regions needed to fabricate p-n junction-based two-dimensional electronic devices.

The end result is a wafer with a layer of n-type rGO on the surface and a layer of p-type rGO underneath. This is critical, because the p-n junction, where the two types meet, is what makes the material useful for transistor applications.

Tags: NCSU Graphene

Visit: http://aip.scitation.org/doi/full/10.1063/1.4979211

Visit: www.mse.ncsu.edu