Nov 16, 2010
Ultrabroadband photodetector made using graphene ink
Graphene – a single atom monolayer of carbon atoms – promises to have many applications. Among many unexpected properties of graphene is that its absorption is almost independent of wavelength. The absorption of graphene, a gapless material, is not high (only 2% for a few monolayers of graphene), but is almost constant across a huge bandwidth from UV to IR domains. In contrast, semiconductors that have a bandgap, display much bigger absorption, but over a narrow bandwidth. Therefore, to cover the UV up to IR band for photodetection we need a considerable number of photodetectors based on semiconductors. Could we come up with a single photodetector able to sense light in the range UV-IR with a reasonable responsivity?
The material for such an ultrabroadband photodetector could be graphene, but the absorption is small. So, we have fabricated an interdigitated electrode on a SiO2/Si substrate and deposited graphene ink on top. The ink consists of monolayer and bilayer graphene flakes dispersed in water and obtained from the company Nanointegris.
We have functionalized the graphene ink with nanoparticles of gold and silver to increase the yield of the photodetection process. The nanoparticles are arranged mainly on the contours of the graphene flakes. To produce more electrons via scattering, it is essential to use nanoparticles of the correct size. Nanoparticles with unsuitable diameters could have an adverse effect by acting as defects or parasitic contacts. Finally, we have "sealed" our photodetector with a bovine serum albumin (BSA) solution.
Extensive and difficult measurements were performed in dc mode, by illuminating our graphene ink photodetector with various lamps to cover the spectrum 200–2500 nm. To our surprise, we have seen significant current changes compared with the dark current for all regions of the spectrum from UV up to IR. The calculated responsivity was about 6–8 mA/W for UV and visible light and 13.7 mA/W for IR.
The detection of light over such a large bandwidth using only drops of pure or functionalized graphene ink opens the door to inexpensive broadband photodetection of light.
This work was published in the journal Nanotechnology.
About the author
The team is from the National Institute for Research and Development in Microtechnologies (IMT), Bucharest, Romania, and the University of Bucharest. Antonio Radoi and Alina Cismaru are postdoctoral researchers supported by the Sectoral Operational Programme Human Resource Development (SOPHRD) under contract number POSDRU/89/1.5/S/63700. Andra Iordanescu is a young scientist now starting her PhD. Mircea Dragoman is a senior scientist at IMT and coordinated the team, which is currently working in the area of graphene applications for high frequencies and biosensing. Daniela Dragoman is a full professor at University of Bucharest, Romania, teaching nanosciences and solid-state physics and with strong research interests in graphene physics and quantum mechanics.