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Graphene, layered materials and hybrid structures for advanced photodetectors


Type

Thesis

Change log

Authors

De Fazio, Domenico 

Abstract

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.

Description

Date

2018-01-19

Advisors

Ferrari, Andrea Carlo

Keywords

Layered Materials, Graphene, Photodetectors

Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge