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$10$\mu$m), where emission from objects at room temperature has a peak. I show graphene-based pyroelectric bolometers with temperature coefficient of resistance up to 900\%/K, two orders of magnitude higher compared to current solutions based on thin oxide membranes. I present flexible photodetectors working in the visible range ($\lambda$=642nm) with gate-tunable graphene/MoS$_2$ 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/MoS$_2$ 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 MoS$_2$ 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 NbSe$_2$ are then studied. I then used NbSe$_2$ ultrathin flakes to realize superconducting photodetectors at $\lambda$=1550nm, reaching a sensitivity down to few thousand photons.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:744461 |
| Date | January 2018 |
| Creators | De Fazio, Domenico |
| Contributors | Ferrari, Andrea Carlo |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.repository.cam.ac.uk/handle/1810/270835 |
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