EPSRC CDT in Metamaterials: Flexible Hyperspectral Infrared Detectors

University of Exeter - Departments of Physics and Astronomy, and Department of Engineering

The studentship is part of the EPSRC Centre of Doctoral Training in Metamaterials (XM2), www.exeter.ac.uk/metamaterials. Our aim is to undertake world-leading research, while training scientists and engineers with the relevant research skills and knowledge, and professional attributes for industry and academia.

Joint supervisors: Prof Saverio RussoProf Monica Craciun

Future progress in the fields of healthcare, food safety and data communication is expected to rely on autonomous sensing and signalling abilities of various objects1, the so-called “internet of things”. To this end, there is an ever-growing need for new photodetection platforms, specifically in the infrared (IR) regime that can provide chemical information, as well as carry communication data. These detectors need to be flexible and transparent, while retaining a high performance speed and a wide range of wavelengths.  

The goal of this project is to achieve an efficient, hyperspectral photodetection (simultaneous detection of several wavelengths) by harvesting the optical activity of plasmonic nanostructures in conjunction with the electric field tuneable energy-gap inherent to bilayer graphene.  To this end, we will construct a stacked device, consisting of an active bilayer graphene absorber, sandwiched between two dielectric layers and two gates. One gate electrode will be a continuous sheet whereas the other electrode will be patterned with a periodic array of discs. Different array periodicity in different regions will enable the hyperspectral response of the device, thus allowing us to pioneer a new class of graphene-based photodetectors with (1) tuneable absorption cut-off wavelength and (2) plasmon enhanced light absorption, thus achieving unprecedented detectivity. The essential requirements for the gate electrodes are (1) high optical transparency, (2) high electrical conductivity and (3) plasmonic response in the wavelength of interest to the photodetection. To date, the only graphene-based material that meets the three aforementioned mandatory requirements is few-layer graphene intercalated with FeCl3. This is the best known graphene-based transparent conductor with transparency in the visible wavelength > 87% and a room temperature resistivity < 8Ohm/□. Furthermore, in graphene nano-structures the plasmon frequency scales as ℏ𝜔∝𝑛1/4, where ℏ is the reduced Planck constant, 𝜔 is the resonance frequency, and 𝑛 is the density of free charge carriers. For this reason, resonance frequencies in the range of infrared can only be achieved by a high charge density. FeCl3-FLG is the highest known p-doped graphene material and is therefore the best material choice for the top electrode.

4-year studentship: for UK/EU students, the studentship includes tuition fees and an annual stipend equivalent to current Research Council rates; for international students (non-EU) a very small number of fees only studentships may be available

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