Imagine a camera using a high-performance sensor that is super sensitive to light and captures high resolution pictures… with only a few pixels. Such a sensor would be made of graphene, which is an extremely thin (one single atomic) layer of carbon. The reason why such sensors have not yet made it into the consumer market is that typical photodetectors made of graphene have only a small area that is sensitive to light, thus severely limiting their performance.
“In most cameras you need lots of pixels,” said Igor Jovanovic, a professor of nuclear engineering and radiological sciences at the University of Michigan. “However, our approach could make possible a very sensitive camera where you have relatively few pixels but still have high resolution.”
Now, researchers at Purdue, the University of Michigan and Pennsylvania State University have discovered a way to solve this problem by combining graphene with a comparatively much larger silicon carbide substrate, creating graphene field-effect transistors, or GFETs, which can be activated by light.
The interesting thing is that the device is responsive to light even when the silicon carbide is illuminated at distances far from the graphene. The light doesn’t have to hit the graphene itself. The semiconductor provides the media that interact with light so that when light comes in, part of the device becomes conducting and that changes the electric field acting on the graphene. The phototransistor is also “position-sensitive,” meaning it can determine the location from which the light is coming, which is important for imaging applications and for detectors.
In the following video, Yong Chen (Purdue University Professor of Physics and Astronomy & Electrical and Computer Engineering, and Director of the Purdue Quantum Center) and Ting-Fung Chung (Purdue graduate student, Physics & Astronomy) explain how this graphene photo-actuated transistor works: