Graphene, layered materials and hybrid structures for advanced photodetectors

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 $\lambda$=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\sim$10μm), where emission from objects at room temperature has a peak. I show graphene-based pyroelectric bolometers with temperature coefficient of resistance up to 900\%/K, two orders of magnitude higher compared to current solutions based on thin oxide membranes. I present flexible photodetectors working in the visible range ($\lambda$=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 $\lambda$=1550nm, reaching a sensitivity down to few thousand photons.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2018

Author dc:creator

• De Fazio, Domenico

Advisor dc:contributor.advisor

• Ferrari, Andrea Carlo

• Layered Materials
• Graphene
• Photodetectors

Licence

• https://www.repository.cam.ac.uk/bitstreams/94564161-5d6c-4a4b-a8d3-1d41b893cdac/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

en

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.17762

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/270835