IEEE Spectrum: Assistant Professor Wang Qijie from Singapore’s Nanyang Technological University (NTU) presents a graphene image sensor that is said to be 1,000 times more sensitive to light than current imaging sensors found in today’s cameras. Apparently, this claim comes from a photoconductive gain of 1,000 achieved by the device. The new sensor is said to use 10 times less energy as it operates at lower voltages. When mass produced, graphene sensors are estimated to cost at least five times cheaper, not clear why.
Prof. Wang Qijie believes this to be the first time that a broad-spectrum, high photosensitive sensor has been developed using pure graphene. Prof Wang came up with an idea to create nanostructures on graphene which will “trap” light-generated electron particles for a much longer time, resulting in a much stronger electric signal.
The “trapped electrons” is the key to achieving high photoresponse in graphene, which makes it far more effective than the normal CMOS or CCD image sensors, said Asst Prof Wang. Essentially, the stronger the electric signals generated, the clearer and sharper the photos (the above description strongly points to photoconductive gain).
"The performance of our graphene sensor can be further improved, such as the response speed, through nanostructure engineering of graphene, and preliminary results already verified the feasibility of our concept," Asst Prof Wang added.
This research, costing about $200,000, is funded by the Nanyang Assistant Professorship start-up grant and supported partially by the Ministry of Education research grants. Development of this sensor took Asst Prof Wang a total of 2 years to complete. His team consisted of two research fellows, Dr Zhang Yongzhe and Dr Li Xiaohui, and four doctoral students Liu Tao, Meng Bo, Liang Guozhen and Hu Xiaonan, from EEE, NTU. Two undergraduate students were also involved.
The new graphene-based sensor is described in this month’s Nature Communications ("Broadband high photoresponse from pure monolayer graphene photodetector"). The next step is to work with industry collaborators to develop the graphene sensor into a commercial product.
From the paper's figures, it appears that the new sensor has a FET-like pixel structure and works best at cryogenic temperatures, such as 12K: