Relazione su invito
High-performance Terahertz nano-detectors based on 2D materials and Van der Walls heterostructures.
The ability to convert light into an electrical signal with high efficiencies and controllable dynamics is a major need in photonics and optoelectronics. In the Terahertz (THz) frequency range, with its exceptional application possibilities in high data rate wireless communications, security, night vision, biomedical or video-imaging and gas sensing, detection technologies providing efficiency and sensitivity performances that can be "engineered" from scratch, remain elusive. These key priorities prompted in the last decade a major surge of interdisciplinary research, encompassing the investigation of different technologies in-between optics and microwave electronics, different physical mechanisms and a large variety of material systems offering $ad hoc$ properties to target the expected performance and functionalities. The talk will provide an overview on our recent developments on THz photodetectors from graphene to novel and fascinating 2D material systems, never exploited before for any active THz device, as topological insulators (TI) black-phosphorus (BP) and bi-dimensional Van der Walls heterostructures combining hexagonal borum nitride (hBN) and BP in a multi-stack configuration. By exploiting the inherent electrical and thermal in-plane anisotropy of a flexible thin flake of BP, we devised plasma-wave, thermoelectric and bolometric nano-detectors with a selective, switchable and controllable operating mechanism as well as near-field THz detection probes. All devices operate at room-temperature in the 0.3--3.8 THz range and are integrated on-chip with planar nano-antennas, which provide remarkable efficiencies through light-harvesting in the strongly sub-wavelength device channel. The achieved selective detection $(\sim$ 5--8 V/W responsivity) and sensitivity performances (signal-to-noise ratio of 500), are here exploited to demonstrate the first concrete application of a phosphorus-based active THz device, for pharmaceutical and quality control imaging of macroscopic samples, in real time and in a realistic setting. We furthermore combine the benefit of the heterostructure architecture with the exceptional technological potential of 2D layered nanomaterials; by reassembling the thin isolated atomic planes of hexagonal borum nitride (hBN) with a few layer phosphorene we stacked mechanically hBN/BP/hBN heterostructures layer-by-layer in a precisely chosen sequence, to devise high-efficiency photodetectors operating in the 0.3--0.65 THz range from 4 K to 300 K with a record S/N = 20000.