Catching Changing Electrical Behavior in Graphene
Graphene is an unusual material with its amazing electrical, optical, and mechanical properties. This makes it of particular interest to many people for use in electronics and sensors, but we are still learning new things about it. Researchers at MIT have recently found that the way graphene interacts with light depends on it electron concentration, which serves to explain contradictions in some previous studies.
When a short, bright pulse of laser light strikes a semiconductor, the pulse increases its conductivity, while the same pulse will decrease the conductivity of a metal. Graphene, an atom-thick sheet of carbon, has been observed to both increase and decrease conductivity under laser pulses, despite the fact that it is typically a metal-like conductor. The MIT researchers discovered that the behavior depends on the electron concentration of the graphene, with a low concentration causing its photoresponse to be like a semiconductor and a high concentration causing it to behave like a metal. To find this result, the researchers placed the graphene on top of an insulator with an electrode beneath it, and then used one laser to provide the pulse and another to measure the conductivity. This all-optical, non-contact approach allowed for the electrical response to be measured within a trillionth of a second.
Now armed with this information, researchers can develop and improve advanced, highly sensitive light detectors made of graphene. These detectors could have ultrafast response times and respond to a broad spectrum of frequencies.