Progress in the research of graphene high-performance optical devices

　　The ultra-thin carbon layer has unique optical and electronic properties, and graphene is expected to be made into high-performance optoelectronic devices. However, the usual graphene photodetector has only a small area that is sensitive to the light beam, which limits its application.

　　Recently, research teams from Purdue University, University of Michigan, and Pennsylvania State University claimed that they have solved the problem that hinders the development of graphene high-performance optical devices. Graphene high-performance optical devices can be used for imaging, display, sensors, and high-speed communications.

　　The paper titled "Position dependence and millimeter-range photodetection of phototransistors made of silicon carbide substrates combined with micron-scale graphene" was published in the journal Nature Nanotechnology. The project is jointly funded by the National Science Foundation and the US Department of Homeland Security. At the same time, it is also funded by the Defense Threat Reduction Agency.

　　The ultra-thin carbon layer has unique optical and electronic properties, and graphene is expected to be made into high-performance optoelectronic devices. However, the usual graphene photodetector has only a small area that is sensitive to the light beam, which limits its application.

　　Professor Chen Yong from Purdue University said: "In order to solve this problem, researchers combined graphene with a relatively large SiC substrate to make a graphene field-effect transistor, which can be activated by light."

　　High-performance photodetectors can be used for high-speed communications, ultra-sensitive cameras, sensors and wearable electronic devices. Graphene-based transistor arrays can achieve high-resolution imaging and display.

　　Professor Igor Jovanovic of Nuclear Engineering and Radiology at the University of Michigan said: "Most cameras require a lot of pixels. However, our method makes ultra-sensitive cameras possible. Although it has relatively few pixels, the resolution is high."

　　Prof. Jovanovic said: “In the usual graphene photodetectors, the light response only occurs at a specific location near the graphene (the area is much smaller than the device size). However, for many optoelectronic device applications, it is hoped that the Obtain light response and position sensitivity over a large area."

　　"New findings show that the device can be sensitive to light in non-local areas, even when light is placed on a silicon carbide substrate at least 500 µm away from graphene. The photoresponse and photocurrent can be increased by as much as 10 times, depending on which part of the material is irradiated. In addition, the new phototransistor technology is also position sensitive, so it can determine where the light reaches (very important for imaging applications and detectors).

　　This is the first demonstration that a small piece of graphene is used on a larger silicon carbide wafer to achieve non-local photodetection, so the light does not have to hit the graphene itself. Light can be incident on a larger area, almost a millimeter, no one has done relevant research before.

　　A voltage is applied between the back surface of the silicon carbide and the graphene to create an electric field in the silicon carbide. The incident light generates photocarriers in the silicon carbide.

　　The research is related to the development of graphene sensors, which can be used to detect radiation.

　　Professor Chen Yong said: “This paper is related to the sensor used to detect photons, but the principle is the same as other types of radiation. We are using sensitive graphene transistors to detect changes in the electric field generated by photons. In this case, light interacts with silicon carbide. It reacts at the bottom."

　　Jovanovic said: "Photodetectors can be used for scintillators, and scintillators can detect radiation. Ionizing radiation produces short-term light, and the photomultiplier tube (about a century old technology) in the scintillator can detect it. Therefore, development can achieve the same function. , Advanced semiconductor-based devices are very interesting things."

　　In addition, the researchers also explained other findings of the computational model. The new transistor was made by the BAK Nanotechnology Center in Purdue Discovery Park.

　　Future research will include exploration of work such as scintillators, astrophysics imaging technology and high-energy radiation sensors.