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Graphene, layered materials and hybrid structures for advanced photodetectors



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De Fazio, Domenico 


Photodetectors are essential in optoelectronics as they allow the conversion of optical signals into electrical outputs. Silicon, germanium and III-V semiconductors currently dominate the photodetector market.

In this dissertation I exploit the potential of layered materials to demonstrate a class of photodetectors able to challenge existing technological issues. I first demonstrate a fabrication method for high-mobility, chemical-vapour-deposited graphene devices which could help to increase the responsivity in graphene-based photodetectors.

I then show three examples of graphene-based Schottky photodetectors working at the telecommunication wavelength λ=1550nm, two for free-space illumination and one for on-chip applications. These are able to achieve responsivities up to 1A/W with relatively-low operation voltage (-3V), similar to those achieved with germanium.

I then target the mid-infrared range ($\lambda\sim10\mu$m), where emission from objects at room temperature has a peak. I show graphene-based pyroelectric bolometers with temperature coefficient of resistance up to 900%/K, two orders of magnitude higher compared to current solutions based on thin oxide membranes.

I present flexible photodetectors working in the visible range (λ=642nm) with gate-tunable graphene/MoS2 heterostructures and show responsivity up to 45A/W, 82% transparency, and low voltage operation (-1V). The responsivity is two orders of magnitude higher compared to semiconducting flexible membranes. Graphene/MoS2 photodetectors can be bent without loss in performance down to a bending radius of 1.4cm.

I finally report on the investigation of superconducting properties of layered materials with the target of realizing ultra-sensitive superconducting photodetectors. Unconventional superconductivity is induced in graphene by proximity with a cuprate superconductor. I used gating to turn semiconducting, few-layer MoS2 into a superconductor, which allowed us to unveil the presence of a multi-valley transport in the superconducting state. Electrical properties of the layered superconductor NbSe2 are then studied. I then used NbSe2 ultrathin flakes to realize superconducting photodetectors at λ=1550nm, reaching a sensitivity down to few thousand photons.





Ferrari, Andrea Carlo


Layered Materials, Graphene, Photodetectors


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge