Final Report Summary - COQUADOT (Colloidal quantum dot infrared photodetectors) In this project we designed and developed novel photodetector schemes for high sensitivity optical sensing in the visible and infrared part of spectrum. We explored 2 main research avenues:1. Colloidal quantum dot photodetectors in which light is absorbed by colloidal quantum dots, the spectral sensitivity of which can be readily tuned via the quantum size effect in colloidal quantum dots. In this thrust we explored various avenues of increasing sensitivity in these devices:a. Plasmonically enhanced colloidal quantum dot photodetectors in which the responsivity is boosted via increased light coupling offered by integrated plasmonic structures including random metal nanoparticle scatterers, near-field enhancement from small metal nanoparticles, as well as metallic gratings acting as surface plasmon polariton couplers in thin film colloidal quantum dot photodetectors. In the context of this project we also investigated novel plasmonic nano-focusing architectures based on bull´s eye gratings that focus incident light from an optical area of several tens of square microns down to a few hundreds of square nanometers where the active volume of a colloidal quantum dot nanoscale photodetector resides offering significant performance enhancement in terms of color selectivity and sensitivity offered by the resonance of the bull´s eye structure.b. We developed novel hybrid photodetectors based on graphene and other 2-dimensional semiconductors coupled with colloidal quantum dots. These operate as photogated transistors in which the channel consists of a high-mobility layered material (graphene or MoS2) whose conductivity can be modulated by light absorption in the quantum dot layer, acting thus as a photogate. This was found to lead to unprecedented responsivities of several million of A/W and record sensitivities expressed in D* on the order of 5 1013 Jones. These detectors have been developed to operate both in the visible as well as in the infrared part of spectrum, determined by the optical absorption of the colloidal quantum dot film.2. Hot carrier plasmonic based photodetectors in which we overcome the bandgap limitation of traditional semiconductor photodetectors as these detectors rely on the excitation of hot carrier in a metal nanostructure. The metallic nanostructure has been designed to excite hybrid local surface plasmons as well as hybrid propagating surface plasmon modes the inter-coupling of which facilitates strong hot carrier generation at the interface of the metal with a transparent semiconductor. The result is the achievement of spectral responsivity determined by the geometry of the metallic nanostructure and not the bandgap of the semiconductor and can thus be tailored to cover spectral range from the visible to the infrared. This will open new ways of optical sensing and may lead to low-cost infrared photodetectors.
