Trouble in Your Tank: HDI and UHDI—Building the Foundation of Advanced Packaging
It’s Only Common Sense: Look Beyond the Tariffs
The Chemical Connection: Employee and Operator Empowerment in the Age of AI
New findings show the device is responsive to light even when the silicon carbide is illuminated at distances far from the graphene. The performance can be increased by as much as 10 times depending on which part of the material is illuminated. The new phototransistor also is “position-sensitive,” meaning it can determine the location from which the light is coming, which is important for imaging applications and for detectors.
“This is the first time anyone has demonstrated the use of a small piece of graphene on a large wafer of silicon carbide to achieve non-local photodetection, so the light doesn’t have to hit the graphene itself,” Chen said. “Here, the light can be incident on a much larger area, almost a millimeter, which has not been done before.”
A voltage is applied between the back side of the silicon carbide and the graphene, setting up an electric field in the silicon carbide. Incoming light generates “photo carriers” in the silicon carbide.
“The semiconductor provides the media that interact with light,” Jovanovic said. “When light comes in, part of the device becomes conducting and that changes the electric field acting on graphene.”
This change in the electric field also changes the conductivity of graphene itself, which is detected. The approach is called field-effect photo detection.
The silicon carbide is “un-doped,” unlike conventional semiconductors in silicon-based transistors. Being un-doped makes the material an insulator unless it is exposed to light, which temporarily causes it to become partially conductive, changing the electric field on the graphene.
“This is a novelty of this work,” Chen said.
The research is related to work to develop new graphene-based sensors designed to detect radiation and was funded with a joint grant from the National Science Foundation and the U.S. Department of Homeland Security and another grant from the Defense Threat Reduction Agency.
“This particular paper is about a sensor to detect photons, but the principles are the same for other types of radiation,” Chen said. “We are using the sensitive graphene transistor to detect the changed electric field caused by photons, light in this case, interacting with a silicon carbide substrate.”
Light detectors can be used in devices called scintillators, which are used to detect radiation. Ionizing radiation creates brief flashes of light, which in scintillators are detected by devices called photo multiplier tubes, a roughly century-old technology.
“So there is a lot of interest in developing advanced semiconductor-based devices that can achieve the same function,” Jovanovic said.
The paper was authored by former Purdue postdoctoral research associate Biddut K. Sarker; former Penn State graduate student Edward Cazalas; Purdue graduate student Ting-Fung Chung; former Purdue graduate student Isaac Childres; Jovanovic; and Chen.
The researchers also explained their findings with a computational model. The transistors were fabricated at the Birck Nanotechnology Center in Purdue’s Discovery Park.
Future research will include work to explore applications such as scintillators, imaging technologies for astrophysics and sensors for high-energy radiation.
Page 2 of 2
