Washington: Scientists have come up with a simple one-step process that produces both n-type and p-type doping of large-area grapheme surfaces could facilitate use of the promising material for future electronic devices.
By applying a commercially-available spin-on-glass (SOG) material to grapheme and then exposing it to electron-beam radiation, researchers at the Georgia Institute of Technology created both types of doping by simply varying the exposure time. Higher levels of e-beam energy produced p-type areas, while lower levels produced n-type areas.
The technique was used to fabricate high-resolution p-n junctions.
When properly passivated, the doping created by the SOG is expected to remain indefinitely in the grapheme sheets studied by the researchers.
"This is an enabling step toward making possible complementary metal oxide grapheme transistors," said Raghunath Murali, a senior research engineer in Georgia Tech`s Nanotechnology Research Center.
In the new doping process, Murali and graduate student Kevin Brenner begin by removing flakes of grapheme one to four layers thick from a block of graphite.
They place the material onto a surface of oxidized silicon, and then fabricate a four-point contact device.
Next, they spin on films of hydrogen silsesquoxane (HSQ), and then cure certain portions of the resulting thin film using electron beam radiation.
The technique provides precise control over the amount of radiation and where it is applied to the grapheme, with higher levels of energy corresponding to more cross-linking of the HSQ.
"We gave varying doses of electron-beam radiation and then studied how it influenced the properties of carriers in the grapheme lattice," Murali said.
"The e-beam gave us a fine range of control that could be valuable for fabricating nanoscale devices. We can use an electron beam with a diameter of four or five nanometers that allows very precise doping patterns," he added.
Electronic measurements showed that a grapheme p-n junction created by the new technique had large energy separations, indicating strong doping effects, he added.
Researchers elsewhere have demonstrated grapheme doping using a variety of processes including soaking the material in various solutions and exposing it to a variety of gases.
The Georgia Tech process is believed to be the first to provide both electron and hole doping from a single dopant material.
First Published: Sunday, February 14, 2010, 22:03